Fuel cell stack having a water separator on the oxidant discharge line

Abstract

The invention relates to a fuel cell unit (1) for electrochemically generating electrical energy, comprising: stacked fuel cells (4), and the stacked fuel cells (4) form a fuel cell stack (3); an inlet opening (35) for introducing oxidant into the fuel cell stack (3); an outlet opening (36) for letting out the oxidant conducted through the fuel cell stack (3) as oxidant exhaust gas; a discharge shut-off element (40) for opening and closing the outlet opening (36), wherein a water separator (56) is formed between the outlet opening (36) and the discharge shut-off element (40) in the flow direction (52) of the oxidant exhaust gas.

Description

[0001] Description

[0002] title

[0003] Fuel cell unit

[0004] The present invention relates to a fuel cell unit according to the preamble of claim 1 and a fuel cell system according to the preamble of claim 15.

[0005] State of the art

[0006] Fuel cell units, as galvanic cells, convert continuously supplied fuel and oxidant into electrical energy and water via 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 connection to the power grid, in motor vehicles, rail transport, aviation, space travel, and shipping. Fuel cell units consist of multiple fuel cells arranged in a fuel cell stack.

[0007] Within each fuel cell, there is a gas chamber for the oxidizer, meaning a flow chamber for the passage of an oxidizer, such as ambient air containing oxygen. This gas chamber for the oxidizer is formed by channels on the bipolar plate and a gas diffusion layer for the cathode. The channels are thus formed by a corresponding channel structure on the bipolar plate, and the oxidizer, namely oxygen, reaches the cathodes of the fuel cells through the gas diffusion layer. A similar gas chamber for the fuel is formed at each anode.

[0008] Fuel cell systems consist of various components, such as a fuel supply system, an oxidant supply system, and the fuel cell stack. The fuel cells contain a proton exchange membrane for conducting protons. To prevent damage to the proton exchange membrane after the fuel cell system is shut down, it is necessary to use a discharge shut-off valve and a supply shut-off valve in the oxidant lines to prevent the supply of oxidant (in the form of oxygen-rich air) into the oxidant channels of the fuel cell stack. This is achieved by closing the discharge and supply shut-off valves after the fuel cell system is switched off.This allows the residual oxygen in the oxidant channels of the fuel cell stack to be removed by passing fuel through the fuel channels during a remaining period of time, thus preventing damage to the proton exchange membrane.

[0009] After the fuel cell stack is shut down, water flows through an outlet opening to remove oxidizer exhaust gas from the fuel cell stack and reaches the discharge shut-off device. This water freezes at temperatures below 0°C and can damage the discharge shut-off device. Alternatively, when restarting the fuel cell system, the discharge shut-off device may not open, for example, if a flap of the discharge shut-off device becomes blocked, thus preventing restart of the fuel cell system at temperatures below 0°C. Therefore, it is already known to install a temperature sensor and an electric resistance heater on the discharge shut-off device and, optionally, on the supply shut-off device.Before starting or restarting the fuel cell system, the discharge shut-off valve and, optionally, the supply shut-off valve are heated at temperatures below 0 °C or, for example, below 3 °C, to avoid the problems and disadvantages described above due to icing. However, this is complex and expensive. Furthermore, if, for example, the temperature sensor and / or the electric resistance heater malfunctions at temperatures below 0 °C, the fuel cell system cannot be started. Therefore, this procedure is unreliable and highly prone to failure.

[0010] WO 2020 / 177987 A1 discloses a method for operating a fuel cell system with a cathode path, wherein the cathode path serves to supply air to the fuel cell system and wherein a water supply system is provided in the cathode path for humidifying the air in order to keep a membrane of the fuel cell system moist, wherein the method comprises at least one of the following steps: emptying and / or venting the water supply system to avoid ice pressure damage in water-filled components of the fuel cell system.

[0011] CN 214099658 U shows a fuel cell arrangement for a motor vehicle with a water separator in exhaust gas and an exhaust gas filter.

[0012] Disclosure of the invention

[0013] Advantages of the invention

[0014] The inventive fuel cell unit for the electrochemical generation of electrical energy comprises stacked fuel cells, the stacked fuel cells forming a fuel cell stack, an inlet opening for introducing oxidizer into the fuel cell stack, an outlet opening for discharged the oxidizer passed through the fuel cell stack as oxidizer exhaust gas, and a discharge shut-off device for opening and closing the outlet opening. A water separator is formed between the outlet opening and the discharge shut-off device in the direction of flow of the oxidizer exhaust gas. The water separator advantageously prevents water from flowing from the fuel cell stack into the discharge shut-off device, thus advantageously avoiding damage due to ice formation on the discharge shut-off device without the need for a complex electrical resistance heating system with a temperature sensor.

[0015] In a further embodiment, a compound oxidizer discharge line is formed in the direction of flow of the oxidizer exhaust gas between the outlet opening and the discharge shut-off device. This compound oxidizer discharge line is part of the oxidizer discharge line between the discharge shut-off device and the fuel cell stack and can also be partially located within the fuel cell stack and / or by the fuel cell stack or components thereof. In an additional variant, the water separator is designed as a water collection basin for storing and collecting water when the fuel cell unit is switched off.The water collection basin essentially functions to collect flowing water in the compound oxidizing agent discharge line and essentially not as a water separator for the sedimentation of water or moisture due to a separation flow space with a significantly larger flow cross-sectional area for the oxidizing agent exhaust gas than outside the separation flow space.

[0016] In a supplementary embodiment, the water collection basin is designed as a vertically formed, in particular local or constructive, relative depression in the compound oxidizing agent discharge line with respect to the flow space bounded by the compound oxidizing agent line, so that water in the flow space bounded by the compound oxidizing agent discharge line can be introduced into the water collection basin due to gravity.

[0017] In a supplementary embodiment, a gradient towards the water collection basin is formed in the circumferential direction of the compound oxidizing agent discharge line, particularly in the lower 30%, 40%, or 50% of the flow space bounded by the compound oxidizing agent discharge line. The compound oxidizing agent discharge line has, for example, a circular cross-section, such that a gradient towards the inlet opening of the water collection basin is formed at the lower end of the flow space for the oxidizing agent exhaust gas in the circumferential direction.

[0018] Preferably, no opening to the outside is formed in the wall(s) bounding the water collection basin. This results in a simple and reliable design for the water collection basin, and makes it inexpensive to manufacture. After commissioning the fuel cell system, the water accumulating in the water collection basin is carried away by the oxidizer exhaust gas flowing through the compound oxidizer discharge line. A complex system for draining the water from the water collection basin using a valve and a sensor to measure the water level is not required. A permanently present opening or bore for draining water from the water collection basin would disadvantageously cause a continuous release of oxidizer exhaust gas through the opening or bore.

[0019] In another embodiment, the boundary of the flow space of the compound oxidizer discharge line has a gradient in the direction of flow of the oxidizer exhaust gas from the fuel cell stack towards the water collection basin, particularly in the lowest vertically, especially in the lowest 30% or 20% section. This gradient allows water to flow into the water collection basin. Preferably, the compound oxidizer discharge line is attached to the fuel cell stack, and the fuel cell stack is oriented for operation, preferably without any inclination, to determine the gradient. Preferably, the gradient is greater than 1%, 5%, 10%, 20%, or 30%.

[0020] In a supplementary embodiment, the boundary of the water collection basin, in particular a front wall of the water collection basin, is oriented at an acute angle, particularly between 90° and 60°, to the flow direction of the oxidizing agent exhaust gas in a cross-section with a vertical sectioning plane parallel to the flow direction of the oxidizing agent exhaust gas, in order to reduce the pressure loss of the oxidizing agent exhaust gas flowing through the compound oxidizing agent discharge line. This prevents strong turbulence of the oxidizing agent exhaust gas in the compound oxidizing agent discharge line and the correspondingly high pressure losses.

[0021] In a further embodiment, the extent of an inlet opening of the, in particular structural, water collection basin in a horizontal direction in the compound oxidizing agent discharge line in a section with a section plane perpendicular to the flow direction of the oxidizing agent exhaust gas is at least 10%, 20% or 30% of the maximum horizontal extent of the boundary of the compound oxidizing agent discharge line in this section.

[0022] In particular, a vertical elevation is formed in the direction of flow of the oxidizing agent exhaust gas in the compound oxidizing agent discharge line at a lower, vertically directed area, especially the lowest 30% or 20% of the flow space, to act as a barrier for the water flowing at this lower, vertically directed area, forming a water collection basin as a local depression. Preferably, the vertical extent of the elevation is less than 30% or 20% of the maximum vertical extent of the flow space of the compound oxidizing agent discharge line.

[0023] In an additional variant, the compound oxidizing agent removal line is formed by an outlet sensor block.

[0024] In a further embodiment, at least one sensor opening, in particular at least one sensor bore, is formed in the outlet sensor block for receiving a temperature sensor and / or pressure sensor. Preferably, the sensor opening for the temperature sensor is designed as a blind bore. Preferably, the sensor opening for the pressure sensor is designed as a through bore opening into the flow space of the outlet sensor block.

[0025] In another variant, a temperature sensor and / or pressure sensor is arranged in at least one sensor opening of the outlet sensor block.

[0026] Preferably, the outlet sensor block includes a flange for attachment to the outlet opening of the fuel cell stack.

[0027] Inventive fuel cell system for converting chemical energy into electrical energy, comprising at least one fuel cell unit, at least one oxidant supply system for oxidant, at least one fuel supply system, at least one cooling system, wherein the fuel cell unit is designed as a fuel cell unit as described in this patent application.

[0028] In a further embodiment, a supply shut-off device and / or an inlet sensor block is integrated into the oxidant supply line. Preferably, a temperature sensor and / or a pressure sensor is integrated into the inlet sensor block. In an additional embodiment, a circumferential groove for receiving a seal is formed in the flange for connection to the fuel cell stack and / or in the flange for connection to the discharge shut-off device, and preferably a seal, in particular an O-ring seal, is arranged in the groove.

[0029] In a complementary variant, the separation of water from the oxidizer exhaust gas in the water separator is carried out as a mechanical water separator with a separation flow chamber by means of sedimentation and / or swirl. In separation by swirl, for example, the oxidizer exhaust gas is set into a rotational motion in a cyclone, so that water separates out due to the centrifugal forces that occur.

[0030] In a supplementary embodiment, the water separator comprises a separation flow chamber for passing through the oxidizing agent exhaust gas and for separating water and / or moisture from the oxidizing agent exhaust gas.

[0031] Preferably, the cross-sectional area of ​​the separation flow space, particularly in a section perpendicular to the flow direction of the oxidizing agent exhaust gas through the compound oxidizing agent discharge line, corresponds substantially, particularly with a deviation of less than 30%, 20% or 10%, to the cross-sectional area of ​​the flow space of the compound oxidizing agent discharge line outside the separation flow space, particularly without taking into account the volume of the water collection basin.The separation flow space at the water collection basin is not significantly larger in terms of flow cross-sectional area than outside the separation flow space, so that separation by sedimentation is not possible due to a significantly reduced flow velocity of the oxidizing agent exhaust gas with a significantly larger flow cross-sectional area of ​​the separation flow space, and separation by sedimentation occurs only very slightly or negligibly.

[0032] In a supplementary embodiment, the separation flow space is formed in sections perpendicular to the flow direction of the oxidizing agent exhaust gas through the compound oxidizing agent discharge line only in sections which intersect the inlet opening of the water collection basin and / or the water collection basin.

[0033] The outlet sensor block is advantageously designed in one piece or in multiple parts and / or at least partially, in particular completely, made of metal, especially brass and / or steel.

[0034] In a further embodiment, the supply valve and / or the discharge valve comprises a flap, in particular a flap pivotable about an axis of rotation, and at least one actuator, in particular an electromagnet and / or an elastic element, in particular a spring, for moving the flap. Preferably, when the electromagnet of the supply valve and / or the discharge valve is not energized, the supply valve and / or the discharge valve is closed. Preferably, when the electromagnet of the supply valve and / or the discharge valve is energized, the supply valve and / or the discharge valve is open.

[0035] Ideally, the dehumidifier includes at least one membrane for transferring moisture and / or water.

[0036] In a supplementary embodiment, the at least one gas conveying device is designed as a blower and / or compressor and / or compressor.

[0037] In a further embodiment, the fuel cells each comprise an ion exchange membrane, in particular a proton exchange membrane and / or anion exchange membrane, an anode, a cathode, at least one gas diffusion layer and a bipolar plate.

[0038] Preferably, the fuel is hydrogen, hydrogen-rich gas, reformate gas or natural gas.

[0039] Advantageously, the fuel cells and / or fuel cell components are essentially flat and / or disc-shaped. In another embodiment, the fuel cell unit comprises a housing and / or a connection plate. The fuel cell stack is enclosed by the housing and / or the connection plate. Preferably, the fuel cell unit comprises the fuel cell stack and, more preferably, the housing.

[0040] In a complementary variant, the oxidizing agent is air with oxygen or pure oxygen.

[0041] Preferably, the fuel cell unit is a PEM fuel cell unit with PEM fuel cells, or a SOFC fuel cell unit with SOFC fuel cells, or an alkaline fuel cell (AFC).

[0042] Brief description of the drawings

[0043] Exemplary embodiments of the invention are described in more detail below with reference to the accompanying drawings. These show:

[0044] Fig. 1 shows a highly simplified representation of a fuel cell system,

[0045] Fig. 2 shows a highly simplified representation of a fuel cell stack, a

[0046] discharge shut-off device and an outlet sensor block in a first embodiment,

[0047] Fig. 3 shows a highly simplified representation of the fuel cell stack, the discharge shut-off device and the exhaust sensor block in a second embodiment.

[0048] Fig. 4 shows a perspective view of an exhaust sensor block in a third embodiment with construction details.

[0049] Fig. 5 shows another perspective, partially cut-away view of the outlet sensor block according to Fig. 4,

[0050] Fig. 6 is a front view of the exhaust sensor block according to Fig. 4, Fig. 7 is a horizontal longitudinal section AA according to Fig. 6 of the exhaust sensor block and

[0051] Fig. 8 shows a vertical longitudinal section BB according to Fig. 6 of the outlet sensor block.

[0052] Figure 1 shows a fuel cell unit 1 as a fuel cell stack 3. The fuel cell unit 1 comprises the fuel cell stack 3, a housing 13, and a connection plate 15. The housing 13 defines an interior space 14. The connection plate 15 also functions as a housing 13 and is fixed to the rest of the housing 13 by fixing elements 16, in particular screws 17. Fuel cells 4, specifically PEM fuel cells 5, are stacked and aligned within the fuel cell stack 3. Due to the large number of stacked fuel cells 4, approximately 300 to 400, not all of them are shown in Figure 1 for the sake of simplicity. The principle of fuel cells 4 is that electrical energy, or electric current, is generated by means of an electrochemical reaction.Hydrogen (H₂) is fed to an anode (not shown) as a gaseous fuel for recirculation, with the anode forming the negative terminal. A gaseous oxidizing agent, namely air containing oxygen, is fed to a cathode (not shown); that is, the oxygen in the air provides the necessary gaseous oxidizing agent. Reduction (electron gain) takes place at the cathode. Oxidation (electron release) occurs at the anode. The fuel cells 4 also include an ion exchange membrane, specifically a proton exchange membrane (PEM), which is positioned between the anode and the cathode. The electrodes, the anode and cathode (not shown), are located on both sides of the PEM, facing the gas spaces. A unit consisting of the PEM, anode, and cathode is called a membrane electrode assembly (MEA) (not shown).A gas diffusion layer (GDL) lies on top of the anode and the cathode. A bipolar plate (not shown) rests on the GDL. The electrically conductive bipolar plate serves as a current collector, for water drainage, and for conducting the reaction gases. In the fuel cell unit 1, the fuel cells 4 are arranged between two clamping elements 18, which act as clamping plates 19. An upper clamping plate 20 rests on the uppermost fuel cell 4, and a lower clamping plate 21 rests on the lowermost fuel cell 4. The clamping elements 18 exert a compressive force on the fuel cells 4; that is, the upper clamping plate 20 exerts a compressive force on the uppermost fuel cell 4, and the lower clamping plate 21 exerts a compressive force on the lowermost fuel cell 4.The fuel cell stack 3 is thus clamped to ensure the tightness of the fuel, oxidizer, and coolant, particularly due to elastic seals, and also to minimize the electrical contact resistance within the fuel cell stack 3. To clamp the fuel cells 4 with the clamping elements 18, four connecting devices 22 are formed as bolts 23 on the fuel cell unit 1, which are subjected to tensile stress. The four bolts 23 are rigidly connected to the clamping plates 19.

[0053] The connection plate 15 and the lower clamping plate 21 each have an opening for introducing recirculating fuel into the recirculating fuel channels. They also each have an opening for discharging recirculating fuel from the recirculating fuel channels. The connection plate 15 and the lower clamping plate 21, as clamping elements 18, each have an inlet opening 35 for introducing oxidizer and an outlet opening 36 for discharging oxidizer, as well as openings (not shown) for introducing and discharging coolant. Thus, the connection plate 15 and the lower clamping plate 21 have a total of six openings (only partially shown in Fig. 1).

[0054] A fuel cell system 2 comprises, in addition to the fuel cell unit 1, an oxidant supply system 26 for supplying the fuel cell stack 2 with air as the oxidant. The oxidant supply system 26 includes a gas conveying device 27, for example, a blower, a compressor, a turbo compressor driven by an electric motor (not shown) and / or a turbine 64, and oxidant lines 28 as oxidant supply line 24 and oxidant discharge line 25, as well as a humidifier 37. In addition to the fuel cell unit 1, the fuel cell system 2 also includes a fuel supply system 29 for supplying the fuel cell stack 3 with hydrogen as fuel. The fuel supply system 29 includes a pressure vessel 30, a fuel line 31 as a process fluid line, valves (not shown) for fuel,in particular an injector (not shown) for controlling the volume flow of fuel introduced from the fuel line 31 into the recirculation fuel line 32, a heat exchanger (not shown) for fuel, a pressure reducer (not shown), a recirculation fuel line 32 as a process fluid line, a recirculation fuel conveying device 33, an electric motor (not shown) for driving the recirculation fuel conveying device 33 and a water separator 34 for separating water from the recirculation fuel, a water tank (not shown) for collecting the water collected in the water separator 34,A drain valve (not shown) for draining water from the water tank and a purge valve (not shown) for releasing recirculated fuel into the environment. In the fuel supply system 29 for supplying the fuel cell stack 3 with hydrogen as fuel, the hydrogen stored in the pressure vessel 30 at a high pressure of, for example, 400 bar is fed to the fuel cells 4 via the fuel line 31. After the fuel has passed through the fuel cells 4, the hydrogen is not completely consumed.so that the hydrogen derived from the fuel cells 4 is fed back to the fuel cells 4 in a closed loop via the recirculation fuel line 32. The recirculation fuel conveying device 33 is used to convey the recirculation fuel through the recirculation fuel line 32. After the fuel has passed through the fuel cells 4, the moisture content of the fuel increases.To prevent excessive water or moisture content in the recirculated fuel, the fuel supply system 29 includes a water separator 34. The water separated in the water separator 34 is collected in the water tank (not shown) and discharged into the environment via the drain valve (not shown). Excess recirculated fuel is discharged into the environment via the purge valve (not shown). In addition to the fuel cell unit 1, the fuel cell system 2 also includes a cooling system (not shown) for temperature control of the fuel cell stack 3, i.e., for cooling the fuel cell stack 3. The cooling system for temperature control of the fuel cell stack 3 includes coolant lines as process fluid lines.a heat exchanger and a pump for circulating the coolant. The coolant is guided through coolant channels in the bipolar plates of the fuel cells 4, and the heat is transferred to the environment via the heat exchanger. In addition to the fuel cell unit 1, the fuel cell system 2 also includes the oxidizer supply system 26, the fuel supply system 29, and the cooling system (not shown) as the coolant supply system.

[0055] The proton exchange membranes of the fuel cells 4 must be sufficiently moistened to conduct protons. For this reason, the fuel cell system 2 has a humidifier 37. The humidifier 37 transfers or conducts moisture and / or water from the oxidant exhaust gas discharged from the fuel cell stack 3 in the oxidant discharge line 25, 28 to the oxidant in the oxidant supply line 24, 28. For this purpose, the humidifier 37 contains corresponding membranes (not shown) for transferring or conducting the moisture and / or water from the oxidant exhaust gas to the oxidant, which is introduced into the fuel cell stack 3.

[0056] After fuel cell system 2 is switched off, a supply shut-off device 38, installed in the oxidant supply line 24, is closed as a supply valve 39, and a discharge shut-off device 40, installed in the oxidant discharge line 25, is closed as a discharge valve 41. After the supply shut-off device 38 and the discharge shut-off device 40 are closed, no more air or oxygen enters the oxidant channels of the fuel cell stack 3. Subsequently, fuel is passed through the fuel channels of the fuel cell stack 3 until the oxygen in the oxidant channels is completely consumed. This is necessary to prevent degradation or damage to the proton exchange membrane. After fuel cell system 2 is switched off, water and moisture remain in the oxidant channels of the fuel cell stack 3.After the fuel cell system 2 is switched off, this water flows through the outlet opening 36 to discharge the oxidizer as oxidizer exhaust from the fuel cell stack 3 into the oxidizer discharge line 25 and thus also into the discharge shut-off device 40. At temperatures below 0°C, this water would impair the function of the discharge shut-off device 40 or damage it, so that the discharge shut-off device 40 could not be opened when the fuel cell system 2 is subsequently started. The supply valve 39 and the discharge valve 41 are, for example, designed as a valve with a flap. In the closed rotary position, the flap rests at its edge against a rubber sealing lip on the housing of the supply valve 39 or the discharge valve 41. When the discharge valve 41 and the supply valve 39 are not energized, they are closed due to a spring that exerts a force, in particular a torque, on the flap.

[0057] The section of the oxidizer discharge line 25 in the direction of flow of the oxidizer exhaust gas between the outlet opening 36 and the discharge shut-off device 40 is designated as a combined oxidizer discharge line 42. A water separator 56, acting as a water collection basin 57, is integrated into this combined oxidizer discharge line 42. The combined oxidizer discharge line 42 between the outlet opening 36 and the discharge shut-off device 40 is designed as an outlet sensor block 43. A temperature sensor for detecting the temperature of the oxidizer exhaust gas and a pressure sensor for detecting the pressure of the oxidizer exhaust gas are integrated into the outlet sensor block 43 (not shown). Similarly, an inlet sensor block 63 with a temperature sensor and a pressure sensor is arranged in the oxidizer supply line 24 between the supply shut-off device 38 and the inlet opening 35.

[0058] Figure 2 shows the basic and fundamental structure of the water separator 56 as a water collection basin 57 within an outlet sensor block 43 in a first embodiment. The outlet sensor block 43, which also functions as the oxidizing agent discharge line 42, has an inlet opening 47 for introducing the oxidizing agent exhaust gas and an outlet opening 49 for discharging the oxidizing agent exhaust gas from the outlet sensor block 43. A flange 46 with bores at the inlet opening 47 serves to provide a fluid-tight connection between the outlet sensor block 43 and the outlet opening 36 of the fuel cell stack 3. A flange 48 with bores at the outlet opening 49 serves to provide a fluid-tight connection with the discharge shut-off device 40. The outlet sensor block 43 defines a flow chamber 50 for the passage of the oxidizing agent exhaust gas at a boundary 51, which is a radial inner surface.The water collection basin 57 is designed as a relative constructive recess with respect to the boundary 51 and is bounded by an inlet opening 58, a bottom wall 59, a front wall 60, a rear wall 61, and two side walls 62 (not shown in Fig. 2). The constructive water collection basin 57, as the constructive recess, is thus bounded in all directions in a horizontal section perpendicular to the plane of Fig. 2 by the additional constructive walls 60, 61, and 62, solely for the purpose of defining the boundaries of the water collection basin 57. The upper end region of the water collection basin 57 forms the inlet opening 58 of the water collection basin 57. A flow direction 52 of the oxidizer exhaust gas, which flows through the outlet sensor block 43, is a central axis of the water collection basin 57 in a section perpendicular to the plane of Fig. 2.2 circularly bounded flow space 50 without consideration of the water collection basin 57, i.e. in a cross-section outside the water collection basin 57. The front wall 60 and the rear wall 61 and thus the boundary of the water collection basin 57 in the section according to Fig. 2 as a section with a vertical cutting plane and parallel to the flow direction 52 is oriented at an angle α of approximately 90° to the flow direction 52.

[0059] The flow chamber 50 in the region of the inlet opening 58 also forms a separation flow chamber for the separation of water or moisture from the oxidizer exhaust gas by means of sedimentation. However, the flow chamber 50 in the direction of flow of the oxidizer exhaust gas, without taking into account the water collection basin 50 in the direction of flow of the oxidizer exhaust gas, is essentially identical in its cross-sectional area before and after the water collection basin 57, so that only a very small separation of moisture or water by means of sedimentation can be carried out at the water collection basin 57.The primary function of the water separator 56, specifically the water collection basin 57, is not separation by sedimentation, but rather the collection of water after the fuel cell system 2 is switched off. This water flows in a lower, vertically oriented area 54 of the boundary 51 from the outlet opening 36 of the fuel cell stack 3 towards the discharge shut-off device 40. Due to its design as a depression, this water is collected in the water collection basin 57 and cannot flow further to the discharge shut-off device 40. The outlet sensor block 43, particularly the walls 59, 60, 61, and 62 that define the boundaries of the water collection basin 57—i.e., the bottom wall 59, the front wall 60, the rear wall 61, and the side walls 62—does not have any opening, such as a bore, for discharging the water that collects in the water collection basin 57.This advantageously results in a particularly simple design for the outlet sensor block 43 and the water separator 56. After the fuel cell system 2 is restarted, the water that collects in the water collection basin 57 is carried along and / or entrained by the oxidizer exhaust gas flowing at high velocity through the outlet sensor block 43. This process is further enhanced by the thermally conductive mounting of the outlet sensor block 43 with the large-area flange 46, so that the operating temperature of the fuel cell stack 3, which is between approximately 60° and 70°C during operation, is directed into the outlet sensor block 43, thus greatly accelerating the evaporation of the water in the water collection basin 57. This water is then discharged into the environment after passing through the oxidizer discharge line 25.

[0060] Figure 3 shows a second embodiment of the outlet sensor block 43. The following description focuses primarily on the differences compared to the first embodiment shown in Figure 2. In the flow direction 52 of the oxidizer exhaust gas and water from the outlet opening 36 towards the discharge shut-off device 40, there is no downward step in the lower vertical region of the boundary 51, starting with the inlet opening 47 of the outlet sensor block 43 and the water collection basin 57, as is the case in the first embodiment with the rear wall 61. The water collection basin 57 is essentially formed by a front wall 60 as a raised section 66 or a step 67 in the lower vertical region 54 of the flow chamber 50, so that the water collection basin 57 is designed as a local depression within the flow chamber 50.The side wall 62 of the water collection basin 57 is formed in a circular cross-section boundary 51 of the flow space 50 in the outlet sensor block 43 for the oxidizer exhaust gas in a vertical direction 54 below the upper end of the elevation 66.

[0061] Figures 4 to 8 show a third embodiment of the outlet sensor block 43 with detailed design features. The following descriptions primarily focus on additions to the first and second embodiments. The metal outlet sensor block 43 has a sensor opening 44, designed as a sensor bore 44 (a blind bore 44) for receiving the temperature sensor, and a sensor opening 45, designed as a sensor bore 45 (a through bore 45) extending into the flow chamber 50 for receiving the pressure sensor. Additionally, a bore 65 with an internal thread is provided, and a sealing screw (not shown) is screwed into this bore 65. This bore 65 serves as an access opening for the outlet sensor block 43. The water collection basin 57 has a recessed area.The water collection basin 57, as a structural depression, is bounded analogously to the first embodiment according to Fig. 2 by the bottom wall 59, the front wall 60, the rear wall 61, and the two side walls 62, solely to define the boundaries of the water collection basin 57. In the direction of flow 52 of the oxidizer exhaust gas after the inlet opening 58 of the water collection basin 57, the raised section 66 is additionally designed as the step 67. This step 67 further defines a local water collection basin 57, and this local water collection basin 57 is formed vertically 54 above the inlet opening 58 of the structural water collection basin 57 and is bounded vertically 54 upwards by an imaginary horizontal plane at the upper end of the step 67. The upper end of the local water collection basin 57 is oriented horizontally 55.In the circumferential direction 53 of the outlet sensor block 43, the flow chamber 50 is bounded by the circular or cylindrical boundary 51 outside the inlet opening 58. The flow direction 52, as shown in Figures 6, 7, and 8, is a central axis of the outlet sensor block 43. In a further, fourth embodiment of the outlet sensor block 43 (not shown), it is designed analogously to the third embodiment according to Figures 5 to 8, but without the step 67. Thus, in this further fourth embodiment (not shown), the water collection basin 57 is designed merely as a structural recess bounded by the walls 59, 60, 61, and 62.

[0062] Overall, the fuel cell unit 1 and the fuel cell system 2 according to the invention offer significant advantages. The water collection basin 57 is integrated into the compound oxidizing agent discharge line 42, which is the outlet sensor block 43. The water flowing out of the fuel cell stack 3 through the outlet opening 36 after shutdown can thus be collected in the water collection basin 57 and, even in freezing temperatures below 0°C, will not damage the discharge shut-off device 40. The water collection basin 57 has a very simple design, so that the compound oxidizing agent discharge line 42, together with the water separator 56 as the water collection basin 57, is advantageously inexpensive to manufacture and reliable in operation.

Claims

Claims 1. Fuel cell unit (1) for the electrochemical generation of electrical energy, comprising stacked fuel cells (4) and the stacked fuel cells (4) forming a fuel cell stack (3), an inlet opening (35) for introducing oxidizing agent into the fuel cell stack (3), an outlet opening (36) for discharging the oxidizing agent passed through the fuel cell stack (3) as oxidizing agent exhaust gas, a discharge shut-off device (40) for opening and closing the outlet opening (36), characterized in that a water separator (56) is formed in the flow direction (52) of the oxidizing agent exhaust gas between the outlet opening (36) and the discharge shut-off device (40).

2. Fuel cell unit according to claim 1, characterized in that a compound oxidizing agent discharge line (42) is formed in the flow direction of the oxidizing agent exhaust gas between the outlet opening (36) and the discharge shut-off device (40).

3. Fuel cell unit according to claim 1 or 2, characterized in that the water separator (56) is designed as a water collection basin (57) is for storing and collecting water during a switched-off fuel cell unit (1).

4. Fuel cell unit according to claim 3, characterized in that the water collection basin (57) is designed as a relative depression in the compound oxidizing agent discharge line (42) in the vertical direction (54), in particular a local or constructive depression, with respect to the flow space (50) bounded by the compound oxidizing agent discharge line (42), so that water can be introduced into the water collection basin (57) in the flow space (50) bounded by the compound oxidizing agent discharge line (42) due to gravity.

5. Fuel cell unit according to claim 3 or 4, characterized in that a gradient to the water collection basin (57) is formed in the circumferential direction (53) of the compound oxidizing agent discharge line (42), in particular in the lower 30%, 40% or 50% in the vertical direction (54) of the flow space (50) bounded by the compound oxidizing agent discharge line (42).

6. Fuel cell unit according to one or more of claims 3 to 5, characterized in that no opening to the outside is formed on the wall(s) (59, 60, 61, 62) or the walls (59, 60, 61, 62) that define the water collection basin (57).

7. Fuel cell unit according to one or more of the preceding claims, characterized in that a boundary (51) of the flow space (50) of the compound oxidizing agent discharge line (42) has a gradient in the flow direction (52) of the oxidizing agent exhaust gas from the fuel cell stack (3) towards the water collection basin (57) at the lowest area in the vertical direction (54), in particular the lowest 30% or 20% area.

8. Fuel cell unit according to one or more of claims 3 to 7, characterized in that the boundary of the water collection basin (57), in particular a front wall (60, 66, 67) of the water collection basin (57), is aligned in a section with a vertical section plane parallel to the flow direction (52) of the oxidizer exhaust gas at an acute angle (a), in particular between 90° and 60°, to the flow direction (52) of the oxidizer exhaust gas in order to reduce the pressure loss of the oxidizer exhaust gas flowing through the compound oxidizer discharge line (42).

9. Fuel cell unit according to one or more of claims 3 to 8, characterized in that the extent of an inlet opening (58) of the water collection basin (57) in a horizontal direction (55) in the compound oxidizing agent discharge line (42) in a section with a section plane perpendicular to the flow direction (52) of the oxidizing agent exhaust gas is at least 10%, 20% or 30% of the maximum horizontal extent of the boundary (51) of the compound oxidizing agent discharge line (42) in this section.

10. Fuel cell unit according to one or more of claims 3 to 9, characterized in that in the flow direction (52) of the oxidizer exhaust gas in the The compound oxidizing agent discharge line (42) at a lower area in the vertical direction (54), in particular the lowest 30% or 20% area, of the flow space (50) forms a vertical elevation (66) as a barrier for the water flowing at the lower area in the vertical direction (54) to form a water collection basin (57) as a local depression.

11. Fuel cell unit according to one or more of claims 2 to 10, characterized in that the compound oxidizing agent discharge line (42) is formed by an outlet sensor block (43).

12. Fuel cell unit according to claim 11, characterized in that at least one sensor opening (44, 45), in particular at least one sensor bore (44, 45), is formed in the outlet sensor block (43) for receiving a temperature sensor and / or pressure sensor.

13. Fuel cell unit according to claim 12, characterized in that a temperature sensor and / or pressure sensor is arranged in the at least one sensor opening (44, 45) of the outlet sensor block (43).

14. Fuel cell unit according to one or more of claims 11 to 13, characterized in that the outlet sensor block (43) comprises a flange (46) for attachment to the outlet opening (36) of the fuel cell stack (3).

15. Fuel cell system (2) for converting chemical energy into electrical energy, comprising at least one fuel cell unit (1), at least one oxidant supply system (26) for oxidant, at least one fuel supply system (29), at least one cooling system, characterized in that the fuel cell unit (1) is configured according to one or more of the preceding claims.

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