Fuel cell system and motor vehicle with a fuel cell system

Abstract

A fuel cell system (2) comprises at least one fuel cell (4) having an anode (6) and a cathode (8); a hydrogen supply system (12) designed and configured to supply hydrogen gas (42) to the at least one fuel cell (4); and an anode recirculation circuit (18) designed and configured to return a gas mixture (36) exiting the anode (6) of the fuel cell (4) to the anode (6) of the at least one fuel cell (4). The anode recirculation circuit (18) includes a mixer (34) designed and configured to mix the gas mixture (36) exiting the anode (6) of the fuel cell (4) with hydrogen gas (42) supplied by the hydrogen supply system (12) before it is returned to the anode (6) of the at least one fuel cell (4).The mixer (34) comprises a Coanda nozzle (46), or the mixer (34) has an axial flow channel (35) through which the gas mixture (36) exiting the anode (6) of the fuel cell (4) flows in an axial direction (A) through the mixer (34), and an annular hydrogen supply channel (38) which is formed annularly around the axial flow channel (35) and which is fluidically connected to the hydrogen supply system (12) in order to introduce hydrogen gas (42) from the hydrogen supply system (12) into the gas mixture (36) flowing through the axial flow channel (35).

Description

[0001] The invention relates to a fuel cell system and a motor vehicle equipped with a fuel cell system according to the invention. State of the art

[0002] To reduce harmful emissions from motor vehicles, electric motors are increasingly being used in vehicles instead of combustion engines. To supply these electric motors with electrical energy, fuel cells powered by hydrogen can also be used instead of batteries.

[0003] To increase efficiency, fuel cells are often operated in a so-called anode recirculation mode. In this mode, the hydrogen-containing gases exiting the anode of the fuel cell are returned to the anode inlet via an anode recirculation circuit, in order to utilize the hydrogen contained in the gases exiting the anode for energy generation.

[0004] Since nitrogen accumulates in the anode recirculation circuit during fuel cell operation in anode recirculation mode, displacing hydrogen, the hydrogen concentration in the anode recirculation circuit decreases over time. To ensure continuous efficient operation of the fuel cells, fresh hydrogen must be continuously supplied to the gas mixture circulating in the anode recirculation circuit to maintain the hydrogen concentration at a predetermined level.

[0005] It is an object of the invention to provide a fuel cell system with an anode recirculation circuit in which the gas mixture circulating in the anode recirculation circuit is efficiently mixed with freshly supplied hydrogen gas to form a gas mixture that is as homogeneous as possible. Disclosure of the invention

[0006] The invention comprises a fuel cell system with at least one fuel cell having an anode and a cathode; a hydrogen supply system designed and configured to supply hydrogen gas to the at least one fuel cell; and an anode recirculation circuit designed and configured to return a gas mixture exiting the anode of the fuel cell to the anode of the at least one fuel cell. The anode recirculation circuit includes a mixer designed and configured to mix the gas mixture exiting the anode of the fuel cell with hydrogen gas supplied by the hydrogen supply system before it is returned to the anode of the at least one fuel cell. The mixer may include a Coanda nozzle.Alternatively, the mixer has an axial flow channel through which the gas mixture exiting the fuel cell anode flows axially, and a hydrogen supply channel. The hydrogen supply channel is annular around the axial flow channel and fluidically connected to the hydrogen supply system to introduce hydrogen gas from the hydrogen supply system into the gas mixture flowing through the axial flow channel.

[0007] The invention also includes a motor vehicle with at least one electric motor and a fuel cell system according to the invention, which is designed and configured to provide electric current for operating the at least one electric motor in order to drive the motor vehicle.

[0008] A fuel cell system according to the invention, comprising a Coanda nozzle or a mixer with an axial flow channel and an annular hydrogen supply channel extending around the axial flow channel, enables the efficient mixing of the gas mixture circulating in the anode recirculation circuit with fresh hydrogen gas to form a very homogeneous hydrogen-rich gas mixture. With such a homogeneous hydrogen-rich gas mixture, the at least one fuel cell can be operated very efficiently with a high degree of efficiency.

[0009] By supplying a gas mixture that is as homogeneous as possible, the service life of a fuel cell stack containing several fuel cells can be extended, since the fuel cells of the fuel cell stack are subjected to a uniform load when operating with a homogeneous gas mixture.

[0010] Furthermore, the requirements for excess hydrogen in the circulating gas mixture can be reduced, since the improved homogeneity of the gas mixture allows all fuel cells to be supplied more precisely with a near-optimal hydrogen concentration.

[0011] A mixer according to the invention can be implemented in a very compact design, so that the space requirement of a fuel cell system according to the invention does not increase significantly compared to a conventional fuel cell system that does not have a mixer.

[0012] In one embodiment, the anode recirculation circuit includes a jet pump located upstream of the mixer, comprising a drive nozzle and a suction inlet. The drive nozzle is connected to the hydrogen supply system. The suction inlet is connected to the anode recirculation circuit to draw in the gas mixture exiting the anode of at least one fuel cell. A jet pump allows for particularly efficient mixing of the gas mixture exiting the anode and fresh hydrogen gas. Simultaneously, such a jet pump can efficiently drive the gas flow in the anode recirculation circuit without requiring an additional electrical conveying device, such as an electric pump.

[0013] In one embodiment, the fuel cell system has a bypass that allows hydrogen gas from the hydrogen supply system to bypass the jet pump and flow directly to the mixer, without the hydrogen gas passing through the jet pump. With such a bypass, the hydrogen concentration in the gas mixture supplied to the anode of the at least one fuel cell can be increased very efficiently.

[0014] The bypass may include a bypass valve that makes it possible to meter the hydrogen gas supplied through the bypass and thus to adjust the hydrogen concentration in the gas mixture supplied to the anode of at least one fuel cell to a predetermined value.

[0015] In one embodiment, the axial flow channel in the mixer has a diameter in the range of 20 mm to 30 mm, in particular a diameter of 25 mm, and the annular hydrogen supply channel has a thickness in the range of 1 mm to 5 mm.

[0016] A mixer in which the axial flow channel and the annular hydrogen supply channel have the aforementioned dimensions has proven to be particularly efficient in mixing the gas mixture exiting the anode with additional, fresh hydrogen gas.

[0017] The annular hydrogen supply channel can extend completely, i.e. in a full circle, around the axial flow channel.

[0018] In alternative embodiments, the hydrogen supply channel can extend only partially, i.e. in a partial circle over an angle of, for example, 180° or 270°, around the axial flow channel.

[0019] In one embodiment, the Coanada nozzle has a truncated cone that is surrounded by the gas mixture exiting the anode and through which the additionally supplied hydrogen gas flows.

[0020] In one embodiment, the truncated cone of the Coanada nozzle has a length in the range of 10 mm to 30 mm, in particular a length of 20 mm.

[0021] In one embodiment, the circumference of the truncated cone is inclined relative to the longitudinal axis of the truncated cone at an angle α in the range between 25° and 35°, in particular at an angle α of 30°.

[0022] In one embodiment, the truncated cone has a maximum diameter D at its wide end. max in the range of 5 mm to 15 mm, in particular a maximum diameter D max of 10 mm.

[0023] In one embodiment, the truncated cone has a minimum diameter D at its narrow end. m i nin the range of 1 mm to 3 mm, in particular a minimum diameter D min of 2 mm.

[0024] A Coanada nozzle with a truncated cone having the aforementioned dimensions has proven to be particularly efficient in mixing the gas mixture in the anode recirculation circuit with additional, fresh hydrogen gas. Brief description of the characters Fig. Figure 1 shows a schematic view of a fuel cell system according to an embodiment of the invention. Fig. Figure 2 shows a schematic longitudinal section through a mixer of a fuel cell system according to an embodiment of the invention. Fig. Figure 3 shows a schematic cross-section through the [structure / body] in the Fig. 2 mixers shown. Fig. Figure 4 shows a schematic sectional view of a Coanda nozzle as it can be used in a mixer according to an embodiment of the invention. Fig. Figure 5 shows a schematic view of a motor vehicle with a fuel cell system according to the invention. Character description

[0025] Fig. Figure 1 shows a schematic view of a fuel cell system 2 according to an embodiment of the invention.

[0026] The fuel cell system 2 comprises at least one fuel cell 4 with an anode 6 and a cathode 8. A membrane 10, in particular a polymer electrolyte membrane 10, is arranged between the anode 6 and the cathode 8.

[0027] The fuel cell system 2 can in particular have a fuel cell stack containing several fuel cells 4.

[0028] The cathode 8 of at least one fuel cell 4 is supplied with gaseous oxygen (O2), in particular oxygen-containing air 9, from the environment via an oxygen supply system not shown in detail.

[0029] The anode 6 of the least one fuel cell 4 is supplied with hydrogen gas (H2) 42 by a hydrogen supply system 12.

[0030] The hydrogen and oxygen supplied to the fuel cell 4 react at or within the membrane 10 to form water (H₂O). This reaction generates an electrical voltage U between electrodes 6a and 8a, which are located in the anode 6 and cathode 8 of the fuel cell 4, respectively. An electric current can thus be drawn from the fuel cell 4 to operate electrical loads, such as electric motors.

[0031] The one in Fig. The fuel cell system 2 shown also has a cooling system 15 which makes it possible to cool at least one fuel cell 4.

[0032] The hydrogen supply system 12 comprises a hydrogen source 14, for example a hydrogen tank 14 or a hydrogen cylinder 14, which provides hydrogen gas (H2) 42 via a shut-off valve 16.

[0033] Since the hydrogen introduced into the anode 6 of the fuel cell 4 does not completely react to form water when flowing through the anode 6 once, the hydrogen-containing gas mixture 36 flowing out of the anode 6 is returned to the anode 6 by an anode recirculation circuit 18 in order to also be able to use the hydrogen flowing out of the anode 6 to generate electrical energy and thus increase the efficiency of the fuel cell system 2.

[0034] During operation of the at least one fuel cell 4, nitrogen from the air 9, which is supplied to the cathode 8 of the at least one fuel cell 4, also passes through the membrane 10 into the anode 6 and accumulates in the anode recirculation circuit 18 over time. As a result, during operation of the at least one fuel cell 4, the proportion of nitrogen in the gas mixture 36 circulating in the anode recirculation circuit 18 increases at the expense of the hydrogen content.

[0035] In order to keep the hydrogen concentration in the anode recirculation circuit 18 at a predetermined value, fresh hydrogen gas 42 from the hydrogen source 14 is additionally supplied to the gas mixture 36 in the anode recirculation circuit 18 during operation.

[0036] In the anode recirculation circuit 18, a water separator 20 is provided downstream of a gas outlet of the anode 6 in order to separate water contained in the gas mixture 36 exiting from the gas outlet of the anode 6 from the gas mixture 36.

[0037] The water separator 20 is equipped with a drain valve 22, which makes it possible to drain the water separated in the water separator 20 by opening the drain valve 22 from the water separator 20.

[0038] To reduce the nitrogen concentration in the gas mixture 36 in the anode recirculation circuit 18 and to increase the hydrogen content in the gas mixture 36, the anode recirculation circuit 18 is regularly purged with pure hydrogen gas 42. This process is also known as "purging".

[0039] A purge valve 24 is provided at the gas outlet of the water separator 20 for purging the anode recirculation circuit 18. By opening the purge valve 24, nitrogen-rich gas mixture 36 can be discharged from the anode recirculation circuit 18 and replaced by fresh hydrogen gas 42 from the hydrogen source 14 in order to reduce the nitrogen concentration in the anode recirculation circuit 18 and increase the hydrogen concentration in the anode recirculation circuit 18.

[0040] The gas outlet of the water separator 20 is also connected to a suction inlet of a jet pump 26. A drive nozzle of the jet pump 26 is fluidically connected to the hydrogen source 14 via the shut-off valve 16 and a hydrogen metering valve 28.

[0041] The hydrogen gas 42 supplied to the drive nozzle of the jet pump 26 from the hydrogen source 14 drives the jet pump 26. By operating the drive nozzle, the gas mixture 36 exiting the anode 6 of the at least one fuel cell 4 is drawn into the suction inlet of the jet pump 26 after passing through the water separator 20.

[0042] The aspirated gas mixture 36 mixes in and downstream of the jet pump 26 with the hydrogen gas 42 supplied from the hydrogen source 14.

[0043] The gas mixture 37 enriched in this way with fresh hydrogen gas 42 is fed to a gas inlet of the anode 6.

[0044] In order to further increase the hydrogen content in the enriched gas mixture 37 supplied to the anode 6, a fuel cell system 2, which is designed according to an embodiment of the invention, additionally has a bypass 30 which makes it possible to introduce additional hydrogen gas 42 from the hydrogen source 14 past the jet pump 26 into the gas mixture 37 supplied to the anode 6.

[0045] The bypass 30 includes a bypass metering valve 32, which makes it possible to regulate the flow of hydrogen gas 42 through the bypass 30, and a mixer 34.

[0046] The mixer 34 is designed and configured to mix the hydrogen gas 42 flowing through the bypass 30 as efficiently and homogeneously as possible into the gas mixture 36 that flows from the jet pump 26 to the gas inlet of the anode 6 of the at least one fuel cell 4. The mixer 34 should preferably occupy as little installation space as possible.

[0047] The Fig. Figure 2 shows a schematic longitudinal section through a mixer 34 of a fuel cell system 2 according to an embodiment of the invention. Fig. Figure 3 shows a schematic cross-section through the [structure / body] in the Fig. 2 mixers shown 34.

[0048] The one in the Fig. 2 and Fig. The mixer 34 shown in Figure 3 has an axial flow channel 35 through which the gas mixture 36 exiting the jet pump 26 flows in an axial direction A to the gas inlet of the Fig. 2 and Fig. 3 anode 6 not shown, which flows into at least one fuel cell 4.

[0049] The axial flow channel 35 can, for example, have a diameter D in the range of 20 mm to 30 mm, in particular a diameter D of 25 mm.

[0050] A ring-shaped hydrogen supply channel 38 is formed around a section of the axial flow channel 35, which encloses the axial flow channel 35 in a ring shape.

[0051] The ring-shaped hydrogen supply channel 38 can, as in the Fig. 3 shown, completely, i.e. in a full circle of, extending around the axial flow channel 35.

[0052] In alternative embodiments, the hydrogen supply channel 38 can extend only partially, i.e. in a partial circle over an angle of, for example, 180° or 270°, around the axial flow channel 35.

[0053] The annular hydrogen supply channel 38 can extend in the axial direction A over a length L in the range of 40 mm to 100 mm along the axial flow channel 35.

[0054] The annular hydrogen supply channel 38 can, for example, have a thickness d in the range of 1 mm to 5 mm.

[0055] The axial flow channel 35 and the annular hydrogen supply channel 38 can each be designed with a circular cross-section or with a non-circular cross-section, for example with an elliptical cross-section.

[0056] The annular hydrogen supply channel 38 is connected via the bypass metering valve 32 (see Fig. 1) fluidically with the in the Fig. 2 and Fig. 3 hydrogen source 14 (not shown). Thus, hydrogen gas 42 can flow from the hydrogen source 14 into the annular hydrogen supply channel 38 when the shut-off valve 16 and the bypass metering valve 32 are open.

[0057] Several openings 40, in particular a plurality of openings, are formed in the inner wall of the annular hydrogen supply channel 38, which faces the axial flow channel 35. Through these openings 40, hydrogen gas 42, which has been introduced into the annular hydrogen supply channel 38, flows from the annular hydrogen supply channel 38 into the axial flow channel 35 and mixes there with the gas mixture 36 flowing through the axial flow channel 35.

[0058] The openings 40 can be arranged in an annular configuration around the axial flow channel 35. In particular, one or more rings of openings 40 can be formed in the inner wall of the annular hydrogen supply channel 38.

[0059] The openings 40 can, for example, be circular openings with a diameter in the range of 0.1 mm to 1 mm.

[0060] In an alternative embodiment, the mixer 34 can be equipped with a Coanda nozzle 46.

[0061] Fig. Figure 4 shows a schematic sectional view of a mixer 34 with a Coanda nozzle 46, as it can be used in a mixer 34 according to the invention.

[0062] The Coanda nozzle 46 has a housing 48, in particular a cylindrical housing 48. A cylindrical cavity is formed in the housing 48, which can, for example, have a diameter D0 in the range of 30 mm to 40 mm, in particular a diameter D0 of 35 mm.

[0063] The Coanda nozzle 46 comprises a truncated cone 44 in which a central flow channel 45 is formed, extending in axial direction A through the truncated cone 44.

[0064] The hydrogen gas 42 from the bypass 30 is fed into the central flow channel 45 of the Coanda nozzle 46.

[0065] The gas mixture 36 exiting the jet pump 26 is guided in the Coanda nozzle 46 to the outer circumference at the wide end of the truncated cone 44, so that it flows along the outer circumference of the truncated cone 44 to its narrow end.

[0066] Downstream of the narrow end of the truncated cone 44, the gas mixture 36 from the jet pump 26 mixes with the hydrogen gas 42 exiting the central flow channel 45 to form a homogeneous, hydrogen-rich gas mixture 37, which is supplied to the anode 6 of the at least one fuel cell 4.

[0067] The truncated cone 44 of the Coanada nozzle 46 can, for example, have a length or height H in the range of 10 mm to 30 mm along the axial direction A, in particular a length or height H in the range of 20 mm.

[0068] The truncated cone 44 can have a maximum diameter D at its wide end. maxin the range of 5 mm to 15 mm, in particular a maximum diameter D max of 10 mm, and at its narrow end a minimum diameter D min in the range of 1 mm to 3 mm, in particular a minimum diameter D min of 2 mm.

[0069] The outer circumferential surface of the truncated cone 44 can be inclined with respect to the axial direction A or longitudinal axis of the truncated cone 44 at an angle α in the range of 25° to 35°, in particular at an angle α of 30°.

[0070] Fig. Figure 5 shows a schematic view of a motor vehicle 1 which is driven by an electric motor 5 which is supplied with electrical energy by a fuel cell system 2 according to the invention.

[0071] The motor vehicle 1 has four wheels 3 and at least one electric motor 5, which is designed and intended to drive at least two of the four wheels 3 of the motor vehicle 1. The electric motor 5 can also be intended to drive all four wheels 3 of the motor vehicle 1.

[0072] In an alternative embodiment, which is not explicitly shown in the figures, an electric motor 5 can be provided on at least one of the wheels 3, in particular on each of the wheels 3, of the motor vehicle 1 for driving the respective wheel 3.

[0073] The electric motor 5 is supplied with electrical energy via a motor control 7, which is provided by the fuel cell system 2.

[0074] A fuel cell system 2 according to the invention can also be used in motor vehicles 1 that have more or fewer than four wheels 3.

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