DE102021208283A1 - Fuel cell system and recirculation device for recirculating anode exhaust gas in a fuel cell system - Google Patents

Abstract

A recirculation device for recirculating anode exhaust gas in a fuel cell system comprises a fan with a suction port for connection to a fuel outlet of a fuel cell arrangement of the fuel cell system, a pressure port for connection to a fuel inlet of the fuel cell arrangement and an impeller for conveying the anode exhaust gas from the suction port to the pressure port. Furthermore, the recirculation device has a turbine with an inlet for connection to a fuel tank of the fuel cell system, an outlet for connection to the fuel inlet of the fuel cell arrangement and a turbine wheel which is kinematically coupled to the impeller of the fan and which can be flown through the inlet with gaseous fuel from the fuel tank and can be rotated is to drive the impeller of the fan.

Description

technical field

The present invention relates to a fuel cell system and a recirculation device for recirculating anode exhaust gas in a fuel cell system.

State of the art

Fuel cells are increasingly used as energy converters, including in vehicles, to convert chemical energy stored in a fuel, such as hydrogen, directly into electrical energy together with oxygen. Fuel cells typically have an anode, a cathode, and an electrolytic membrane positioned between the anode and the cathode. The fuel is oxidized at the anode and the oxygen is reduced at the cathode. This creates water on the cathode side.

Typically, the anode of fuel cells is continuously supplied with excess gaseous fuel, that is, more fuel than would be stoichiometrically necessary for a given amount of oxygen supplied to the cathode. The excess fuel or the anode output is usually recirculated or fed back to the anode. This is typically done using a recirculation fan that circulates the anode exhaust from an outlet of the anode back to the inlet of the anode.

The recirculation fan is usually operated by an electric motor. To improve the energy efficiency of a fuel cell system is in the DE 10 2007 037 096 A1 discloses driving the recirculation fan by means of a turbine. The turbine uses compressed air as the working fluid, which has been compressed by means of a compressor for supply to the cathode.

Disclosure of Invention

According to the invention, a recirculation device having the features of claim 1 and a fuel cell system having the features of claim 9 are provided.

According to a first aspect of the invention, a recirculation device for recirculating anode exhaust gas in a fuel cell system comprises a fan with a suction port for connection to a fuel outlet of a fuel cell arrangement of the fuel cell system, a pressure port for connection to a fuel inlet of the fuel cell arrangement and an impeller for conveying the anode exhaust gas from the suction port to the Pressure connection and a turbine with an inlet for connection to a fuel tank of the fuel cell system, an outlet for connection to the fuel inlet of the fuel cell arrangement and a kinematically coupled to the impeller of the fan turbine wheel, which can flow through the inlet with gaseous fuel from the fuel tank and is rotatable, to drive the fan impeller.

According to a second aspect of the invention, a fuel cell system comprises a fuel cell arrangement having at least one fuel cell, a fuel inlet and a fuel outlet, and a recirculation device according to the first aspect of the invention, wherein the pressure port of the fan and the outlet of the turbine are connected to the fuel inlet, and wherein the The suction port of the blower is connected to the fuel outlet.

One idea on which the invention is based is to partially break down the kinetic energy of a fuel flow that is supplied to the fuel cell system, e.g. from a tank, in a turbine and to use the turbine to drive a blower in order to recirculate anode waste gas. For this purpose, according to the invention, an impeller of the turbine, which is driven by the fuel, such as hydrogen, and an impeller of the fan, which conveys the anode exhaust gas, are kinematically coupled to one another, e.g. via a shaft, a flange or by the turbine wheel and the impeller being in one piece are trained. Typically, the fuel is present in the tank at a pressure in a range between 8 bar and 20 bar and is supplied to an anode of the fuel cell assembly at a pressure in a range between 1.5 bar and 3.5 bar. The pressure difference can advantageously be reduced in the turbine and used to drive the fan.

By using the kinetic energy of a fuel flow that is supplied to the fuel cell system in a turbine to drive the fan that recirculates the anode exhaust gas, the energy efficiency of the fuel cell system is advantageously improved.

Advantageous refinements and developments result from the further dependent claims and from the description with reference to the figures of the drawing.

According to some embodiments, it can be provided that the turbine wheel has a circular outer circumference, on which a multiplicity of essentially hemispherical streams tion surfaces are formed, with a plurality of nozzles being arranged along the outer circumference, which are oriented tangentially to the outer circumference and are each connected to the inlet. The flow surfaces can thus be concavely curved surfaces which extend hemispherically or essentially hemispherically. The nozzles are aligned so that the gaseous fuel is directed onto the airfoils, turning the fuel and causing the turbine wheel to move. Accordingly, the turbine can be designed as a type of free jet turbine. This advantageously results in a simple structural design of the flow surfaces and uncomplicated flow guidance.

According to some embodiments, it can be provided that the flow surfaces are defined by indentations formed in the outer circumference. The flow surfaces therefore do not protrude radially from the outer circumference, or only insignificantly, and a compact construction of the turbine is advantageously achieved.

According to some embodiments, it can be provided that the turbine wheel is attached to an outer circumference of the impeller of the fan. For example, the turbine wheel and the impeller of the fan can be formed as one piece, with an outer circumference of the impeller of the fan corresponding to the outer circumference of the turbine wheel. An even more compact construction of the recirculation device is thus realized.

According to some embodiments, it can be provided that the blower and the turbine have a common housing, with the blower being designed as a side channel compressor, with which the impeller of the blower has blades on one end face, which face a ring-segment-shaped side channel formed in the housing, wherein the suction port and the pressure port are formed in opposite end portions of the side duct, and wherein the housing has a mixing duct connected to an outlet port to which the outlet of the turbine and the pressure port of the fan are connected. Thus, the side passage in which the anode off-gas is conveyed and a space in which fresh fuel is supplied to the turbine are immediately adjacent with respect to the radial direction, and the fresh fuel and the anode off-gas are mixed directly within the common casing. This achieves an even more compact structure. The outer circumference of the impeller or of the turbine can be surrounded, for example, by a fresh gas channel in the form of a ring segment, into which the nozzles project at predetermined distances from one another. The fresh gas channel can open into the mixing channel.

According to some embodiments, it can be provided that a gap is formed between the end face of the impeller of the fan and a region of the housing radially delimiting the side channel, which gap connects the side channel to a channel formed in the housing, so that liquid water can flow out of the side channel in the radial direction can be removed through the gap. For example, the trough may be separated from the fresh gas channel with respect to an axial direction. Optionally, the channel encloses the impeller or the turbine wheel at least partially and is preferably designed in the form of a ring segment. Due to the rotation of the impeller about an axis of rotation, the anode exhaust gas is accelerated in the radial direction, so that the water contained in the anode exhaust gas is transported radially outwards. The water can be discharged from the side channel in a simple manner through the gap.

According to some embodiments, it can be provided that the recirculation device has a drive device that is kinematically coupled to the impeller of the fan, in particular in the form of an electric motor. The flexibility of the regulation of the mass flow of fuel that is conveyed by the blower can thus be further increased.

According to some embodiments, it can be provided that the recirculation device has a collection container for collecting liquid water that is separated from the anode waste gas in the blower.

According to some embodiments, it can be provided that the collection container is connected to the blower by one or more lines, the line(s) and/or the collection container being thermally coupled to the drive device. For example, the drive can protrude into the collection container or the lines can or the lines can run along the drive device. This improves the cooling of the drive device and thus its service life.

According to some specific embodiments, it can be provided that the pressure connection of the fan and the outlet of the turbine are connected directly to the fuel inlet without an interposed ejector pump. The combination of turbine and fan can advantageously provide the required recirculation mass flow and the required fresh gas mass flow both at high and at low loads, which simplifies the control of the fuel cell system. Furthermore, the flow losses in the system are reduced.

According to some specific embodiments, it can be provided that the fuel cell system has a metering valve connected to the inlet of the turbine, which can be connected to a fuel tank and is set up to vary a fuel mass flow supplied to the turbine from the fuel tank.

According to some embodiments, it can be provided that the fuel cell system has a tank which is connected to the inlet of the turbine.

• 1 eine schematische Darstellung eines hydraulischen Schaltbildes eines Brennstoffzellensystems gemäß einem Ausführungsbeispiel der Erfindung;
• 2 eine Draufsicht auf eine Rezirkulationsvorrichtung gemäß einem Ausführungsbeispiel der Erfindung;
• 3 eine vereinfachte, abgebrochene Schnittansicht der in 2 gezeigten Rezirkulationsvorrichtung.

The invention is explained below with reference to the figures of the drawings. From the figures show:

• 1 a schematic representation of a hydraulic circuit diagram of a fuel cell system according to an embodiment of the invention;
• 2 a plan view of a recirculation device according to an embodiment of the invention;
• 3 a simplified broken sectional view of the in 2 shown recirculation device.

In the figures, the same reference symbols designate identical or functionally identical components, unless otherwise stated.

1 shows a fuel cell system 200 by way of example and in a schematic manner. As in FIG 1 shown by way of example, the fuel cell system 200 may include a tank 205 , a fuel cell assembly 210 , a recirculation device 100 , and a flow control valve 220 .

The tank 205 is designed to store gaseous fuel such as hydrogen at high pressure, eg at a pressure of more than 10 bar. The tank 205 is in 1 purely by way of example as part of the fuel cell system 200 . However, the invention is not limited to this, but the fuel cell system 200 can also be connectable to the tank 205 or another fuel source.

The fuel cell arrangement 210 can have a multiplicity of fuel cells 213 arranged to form a stack. In principle, however, it is also conceivable that only one fuel cell 213 is provided. As in 1 shown schematically, each fuel cell 213 can have an anode 213A, a cathode 213B and an electrolyte 213C arranged between them, for example in the form of an electrolyte membrane.

The fuel cell arrangement 210 has a fuel inlet 211, via which the anode 213A can be supplied with gaseous fuel, e.g. hydrogen or natural gas, and a fuel outlet 212, via which unused or unreacted fuel can be removed from the anode 213A. Unconsumed fuel discharged at fuel outlet 212 may also be referred to as excess fuel or anode exhaust.

As in 1 Also shown, the fuel cell arrangement 210 has an oxygen inlet 214, via which the cathode 213B can be supplied with gaseous oxygen, either as pure oxygen or as oxygen contained in the ambient air, and a product outlet 215, via which unused or unreacted oxygen and chemical reaction products , in particular water, can be discharged from the cathode 213B.

The fuel cell arrangement 210 is supplied with fuel from the tank 205 via a supply line 201 which is connected to the fuel inlet 211 . The anode waste gas or excess fuel exiting at the fuel outlet 212 of the fuel cell arrangement 210 is fed to the recirculation device 100 via a discharge line 202, recirculated by the recirculation device 100 and fed back to the fuel inlet together with fresh fuel.

As in 1 shown schematically, the recirculation device 100 comprises a blower 1 and a turbine 2. Optionally, a drive device 4 and/or a collection container 5 can also be provided, as in FIG 1 shown as an example.

Fan 1 is in 1 shown only symbolically and has a suction port 11 connected to the discharge line 202 and a pressure port 12 connected to the supply line 201 . The fan 1 is designed to convey anode waste gas from the fuel outlet 212 to the fuel inlet 211 .

Turbine 2 is in 1 also shown only symbolically and has an inlet 21 which is connected to the tank 205 and an outlet 22 which is connected to the supply line 201 . The turbine 2 is, as in 1 shown schematically, kinematically coupled to the fan 1. The fuel, which is present at high pressure, can flow through the turbine 2 from the tank 205 and is designed to convert the kinetic energy stored in the flowing fuel and thereby to drive the fan 1 . Thus, in a simple way, the energy efficiency of the fuel cell system 200 can be improved because the power requirement for driving the fan 1 is reduced. As in 1 is also shown schematically, the pressure connection 12 of the blower 1 and the outlet 12 of the turbine 2 can be connected directly, in particular without an interposed ejector pump, to the fuel inlet 211 of the fuel cell arrangement. As a result, the fuel cell system 200 can be made more compact. However, it is not excluded that further flow components such as valves, humidifiers or dehumidifiers or the like are arranged between the pressure connection 12 of the blower 1 and the fuel inlet 211 or the outlet 12 of the turbine 2 and the fuel inlet 211 .

The optional motor 4 can be an electric motor, for example, and is also kinematically coupled to the fan 1 in order to drive it at least in support of the turbine 2 .

The flow control valve 220 can be arranged, for example, between the tank 205 and the inlet 21 of the turbine 2, as is shown in FIG 1 is shown schematically. The flow control valve 220 can in particular be designed to vary a mass flow of fuel that is supplied to the turbine 2 .

2 shows schematically a plan view of an exemplary recirculation device 100 as shown in FIG 1 illustrated fuel cell system 200 may be installed. 3 shows a sectional view of in 2 Device 100 shown. As already explained, the recirculation device 100 has a blower 1 with a suction connection 11 and a pressure connection 12 and a turbine 2 with an inlet 21 and an outlet 22 . As in 2 also visible, the blower 1 has an impeller 10 that can be rotated about an axis of rotation A1 for conveying the anode waste gas from the suction connection 11 to the pressure connection 12 . The turbine 2 has a turbine wheel 20, which can be flown with gaseous fuel from the fuel tank 205 and can be rotated, for example about the same axis of rotation A1 as the impeller 10 of the fan 1. As in FIG 2 is also shown schematically, the recirculation device 100 can also have a housing 3, with the blower 1 and the turbine 2 preferably being housed together in the housing 3.

The fan 1 can be designed in particular as a side channel compressor, as in the 2 and 3 is shown purely as an example. The impeller 10 has at least one or, as in 3 shown, on both axial end faces of a plurality of blades 13 which are arranged distributed along the circumference of the impeller 10. The blades 13 extend substantially along a radial direction R1 that is transverse to the axis of rotation A1. As in the 2 and 3 As shown, the blades 13 may extend between an inner annular support portion 14 with respect to the radial direction R1 and an outer annular shroud 15 with respect to the radial direction R1. As in 2 indicated schematically by dashed lines, the housing 3 has a side channel 30 which extends in the form of a ring segment around the axis of rotation A1 , the suction port 11 and the pressure port 12 being formed at opposite ends of the side channel 30 . The blades 13 face the side channel 30, as is shown in particular in 3 is visible.

The impeller 10 of the fan 1 and the turbine wheel 20 are kinematically coupled to one another, so that the impeller 10 of the fan 1 can be driven by the turbine wheel 20 . In the 2 and 3 is shown purely as an example that the impeller 10 and the turbine wheel 20 are formed as a common wheel. In particular, the turbine wheel 20 can be attached to an outer periphery 10a of the impeller 10 of the fan 1 . For example, the turbine wheel 20 can be formed by the shroud 15 of the impeller 10 of the fan 1, as is shown in 3 is shown schematically. The outer circumference 10a of the impeller 10 and an outer circumference 20a of the turbine wheel 20 can thus both be formed by the shroud 15 . The turbine wheel 20 generally includes a plurality of airfoils 23a constructed and arranged to redirect flow impinging thereon such that momentum of the flow is converted into rotation of the turbine wheel 20 . For example, the flow surfaces 23a can be essentially hemispherical, as in FIG 3 shown. In particular, two hemispherical flow surfaces 23a can be arranged next to one another along the longitudinal axis A1 and separated by a central web 26 . As in 3 Also shown, the flow surfaces 23a may be defined by indentations 23 formed in the outer periphery 20a, for example. A plurality of flow surfaces 23a are provided along the outer circumference 20a of the turbine wheel 20 .

As in 2 shown schematically, a plurality of nozzles 24 can be arranged along the outer circumference 20a of the turbine wheel 20, which are each connected to the inlet 21. In 2 three nozzles 24 are shown purely by way of example. A different number of nozzles can of course also be provided. The nozzles 24 are oriented tangentially to the outer periphery 20a of the turbine wheel 20 to direct fuel onto the airfoils 23a. Thus, a kind of free radiation am realised. As in the 2 and 3 shown schematically, the housing 3 can have a fresh gas channel 35 which extends in the form of a ring segment along the outer circumference 20a of the turbine wheel 20 and into which the nozzles 24 protrude at predetermined intervals. The fresh gas channel 35 is open to the flow surfaces 23a. One end of the fresh gas duct 35 can form the outlet 22 of the turbine 2, for example. Furthermore, a supply channel 36 can be provided, which is connected to the inlet 21 and which is arranged outside of the fresh gas channel 35 with respect to the radial direction R1, as in FIG 2 shown schematically. The nozzles 24 are connected to the supply channel 36 with an input. Furthermore, the supply channel 36 is connected to the fuel tank 205, e.g. via the flow control valve 220. In general, the flow control valve 220 can be attached to the housing 3, for example, and thus integrated together with the blower 1 and turbine 2 to form a unit, as in 2 shown as an example.

As in 2 shown schematically, the housing 3 can have an outlet connection 32 which is provided for connection 32 to the supply line 201 or for connection to the fuel inlet 211 . The fresh gas duct 32 or the outlet 22 of the turbine 2 and the pressure port 12 of the fan 1 can each be connected to a mixing duct 31 which is connected to the outlet port 32, as in FIG 2 shown schematically.

As in 3 also shown schematically and by way of example, the housing 3 can have a channel 34 which at least partially encloses the outer circumference 10a of the impeller 10 or the outer circumference 20a of the turbine wheel 20 . As in 3 shown, the channel 34 is separated from the fresh gas channel 35 along the axis of rotation A1 or in relation to the axial direction and is thus separated from the flow surfaces 23a. A channel 34 can be provided for each side channel 30 . In 3 two troughs 34 are therefore shown. As in 3 Also shown, a gap 33 connecting the side channel 30 to the channel 34 can be formed between the end face of the impeller 10 of the fan 1 and a region of the housing 3 bordering the side channel 30 in the radial direction R1. When the impeller 10 is rotated about the axis of rotation A1, the anode exhaust gas located in the side channel 30 is accelerated in the radial direction R1. Liquid water, which may be contained in the anode waste gas, is conveyed into the radially outer region of the side channel 30 due to its high density compared to the gaseous fuel as a result of the centrifugal force and can be transported through the gap 33 into the channel 34 . As in the 1 until 3 indicated schematically, the channel 34 can be conducted into the collection container 5 via one or more lines 51 .

As in 1 shown purely schematically, the optional drive device 4 can be thermally coupled to the collection container 5 , for example by the drive device 4 protruding into the collection container 5 . Alternatively or additionally, the lines 51 can also be thermally coupled to the drive device 4 .

Although the present invention has been explained above by way of example using exemplary embodiments, it is not limited thereto but can be modified in many different ways. In particular, combinations of the above exemplary embodiments are also conceivable.

QUOTES INCLUDED IN DESCRIPTION

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Patent Literature Cited

• DE 102007037096 A1 [0004]

Claims (10)

Recirculation device (100) for recirculating anode exhaust gas in a fuel cell system (200), comprising: a fan (1) with a suction port (11) for connection to a fuel outlet (212) of a fuel cell assembly (210) of the fuel cell system (200), a pressure port (12) for connection to a fuel inlet (211) of the fuel cell assembly (210) and a Impeller (10) for conveying the anode exhaust gas from the suction port (11) to the pressure port (12); and a turbine (2) having an inlet (21) for connection to a fuel tank (205) of the fuel cell system (200), an outlet (22) for connection to the fuel inlet (211) of the fuel cell assembly (210) and a kinematically connected to the impeller ( 10) of the fan (1) coupled turbine wheel (20), which through the inlet (21) with gaseous fuel from the fuel tank (205) can flow and rotate to drive the impeller (10) of the fan (1). Recirculation device (100) after claim 1 , wherein the turbine wheel (20) has a circular outer periphery (20a) on which a plurality of substantially hemispherical flow surfaces (23a) are formed, and wherein a plurality of nozzles (24) are arranged along the outer periphery (20a) tangentially to the Outer circumference (20a) are aligned and each connected to the inlet (21). Recirculation device (100) after claim 2 wherein the flow surfaces (23a) are defined by indentations (23) formed in the outer periphery (20a). Recirculation device (100) after claim 2 or 3 wherein the turbine wheel (20) is attached to an outer periphery (10a) of the impeller (10) of the fan (1). Recirculation device (100) after claim 4 , the fan (1) and the turbine (2) having a common housing (3), the fan (1) being designed as a side channel compressor, in which the impeller (10) of the fan (1) has blades (13 ) which face a ring-segment-shaped side channel (30) formed in the housing (3), the suction connection (11) and the pressure connection (12) being formed in opposite end regions of the side channel (30), and the housing (3) a mixing duct (31) connected to an outlet port (32) to which the outlet (22) of the turbine (2) and the pressure port (12) of the fan (1) are connected. Recirculation device (100) after claim 5 , wherein a gap (33) is formed between the end face of the impeller (10) of the blower (1) and a region of the housing (3) radially delimiting the side duct (30), which gap connects the side duct (30) with a cavity in the housing (3 ) formed channel (34) connects, so that liquid water from the side channel (30) in the radial direction (R1) through the gap (33) can be discharged. Recirculation device (100) according to any one of the preceding claims, additionally comprising: a drive device (4) kinematically coupled to the impeller (10) of the fan (1), in particular in the form of an electric motor. Recirculation device (100) after claim 7 , additionally comprising: a collection container (5) for collecting liquid water which is separated from the anode exhaust gas in the blower (1), the collection container (5) being connected to the blower (1) by one or more lines (51). , and wherein the line(s) and/or the collection container (5) is thermally coupled to the drive device (4). Fuel cell system (200), with: a fuel cell arrangement (210) with at least one fuel cell (213), a fuel inlet (211) and a fuel outlet (212); and a recirculation device (100) according to any one of the preceding claims; the pressure port (12) of the fan (1) and the outlet (12) of the turbine (2) being connected to the fuel inlet (211); and wherein the suction port (11) of the fan is connected to the fuel outlet (212). Fuel cell system (200) after claim 9 , wherein the pressure connection (12) of the fan (1) and the outlet (12) of the turbine (2) are connected directly to the fuel inlet (211) without an interposed ejector pump.

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