DELIVERY UNIT FOR AN ANODE CIRCUIT OF A FUEL CELL SYSTEM FOR DELIVERING A GASEOUS MEDIUM, AND FUEL CELL SYSTEM

Abstract

Disclosed is a delivery unit (3) for an anode circuit (9) of a fuel cell system (1) for delivering a gaseous medium, in particular hydrogen, from an anode region (38) of a fuel cell (2), said delivery unit (3) comprising at least one jet pump (4) and being at least indirectly fluidically connected to the outlet of the anode region (38) by means of at least one connection line (23, 25) and being fluidically connected to the inlet of the anode region (38) by means of an additional connection line (27). According to the invention, in addition to the jet pump (4), the delivery unit (3) comprises a recirculation fan (8) and a metering valve (6) as other components, and the flow contours of the components (4, 6, 8) for the gaseous medium and/or the components (4, 6, 8) are at least almost entirely arranged in a common housing (7).

Claims

1. A delivery unit (3) for an anode circuit (9) of a fuel cell system (1) for delivering a gaseous medium out of an anode region (38) of a fuel cell (2), wherein the delivery unit (3) comprises at least one jet pump (4), wherein the delivery unit (3) is at least indirectly fluidically connected by at least one connecting line (23, 25) to an outlet of the anode region (38), and wherein the delivery unit (3) is fluidically connected by a further connecting line (27) to an inlet of the anode region (38), wherein the delivery unit (3) further comprises a recirculation blower (8) and a dosing valve (6), wherein the flow contours of the jet pump, dosing valve and recirculation blower (4, 6, 8) for the gaseous medium and/or the jet pump, dosing valve and recirculation blower (4, 6, 8) are arranged at least approximately entirely in a common housing (7).

2. The delivery unit (3) as claimed in claim 1, characterized in that the recirculation blower (8) has a compressor wheel (12) with an encircling outer delimiting ring (39) which runs rotationally symmetrically with respect to an axis of rotation (48) of the compressor wheel (12), and wherein an at least partially encapsulated separation space (34), and/or a discharge channel (46), is situated in the housing (7) of the delivery unit (3) on a side of the compressor wheel (12) which is averted from the axis of rotation (48).

3. The delivery unit (3) as claimed in claim 1, characterized in that a constituent H.sub.2O and/or a constituent N.sub.2 of the gaseous medium is separated off in the recirculation blower (8).

4. The delivery unit (3) as claimed in claim 1, characterized in that the recirculation blower (8) and the jet pump (4) are arranged relative to one another in the common housing (7) such that an axis of rotation (48) of a compressor wheel (12) of the recirculation blower (8) runs at least approximately perpendicular to a longitudinal axis (50) of the jet pump (4).

5. The delivery unit (3) as claimed in claim 1, characterized in that a gas outlet opening (16) of the recirculation blower (8) transitions directly into a first inflow line (28) and/or an intake region (11) of the jet pump (4) and forms an integrated flow channel (41).

6. The delivery unit (3) as claimed in claim 5, characterized in that the integrated flow channel (41) forms a curvature (43) within the common housing (7), wherein a diversion and/or flow guidance of the gaseous medium between the recirculation blower (8) and the jet pump (4) takes place exclusively in a region of the curvature (43).

7. A fuel cell system (1) having a delivery unit (3) as claimed in claim 1 for controlling a feed of hydrogen to and/or a discharge of hydrogen from the fuel cell (2).

8. The fuel cell system (1) as claimed in claim 7, characterized in that a separation of a constituent H.sub.2O and/or of a constituent N.sub.2 from the gaseous medium in the anode circuit (9) is performed by the recirculation blower (8) and/or by a separator (10).

9. The fuel cell system (1) as claimed in claim 8, characterized in that the separator (10) is arranged in the anode circuit (9) upstream of the delivery unit (3) in a flow direction V, wherein the anode region (38) is fluidically connected to the separator (10) by a first connecting line (23), and the separator (10) is fluidically connected to the delivery unit (3) by a second connecting line (25), and the delivery unit (3) is fluidically connected to the anode region (38) by a third connecting line (27).

10. The fuel cell system (1) as claimed in claim 8, characterized in that a discharge of H.sub.2O and/or N.sub.2 from the recirculation blower (8) into the separator (10) takes place in a flow direction VI via a return line (21).

11. The fuel cell system (1) as claimed in claim 10, characterized in that a separation space (34) and/or the discharge channel (46), which are each situated in the housing (7) of the delivery unit (3) on a side of the compressor wheel (12) which is averted from an axis of rotation (48) and are at least partially encapsulated, are at least indirectly fluidically connected to a collecting vessel (31) of the separator (10) via the return line (21), wherein the separation space (34) and/or the discharge channel (46) forms an elevated pressure level in relation to the collecting vessel (31) of the separator (10), and wherein a discharge of H.sub.2O and/or N.sub.2 from the recirculation blower (8) into the separator (10) takes place in the flow direction VI.

12. The fuel cell system (1) as claimed in claim 11, characterized in that the collecting vessel (31) has a discharge valve (44), wherein the discharge valve (44) is arranged in the collecting vessel (31) at a geodetic height that is low during intended use, wherein the discharge of all of the H.sub.2O and/or N.sub.2 out of the region of the anode circuit (9) takes place via the discharge valve (44).

13. The fuel cell system (1) as claimed in claim 9, characterized in that the second connecting line (25) is arranged at a high geodetic height in the collecting vessel (31).

14. The fuel cell system (1) as claimed in claim 13, characterized in that a separating edge (37) is arranged in the collecting vessel (31) such that the inflowing gaseous medium passing from the anode region (38) is diverted and/or split up such that the lightweight constituent H.sub.2 is diverted in a direction of the second connecting line (25), and the heavy constituents H.sub.2O and/or N.sub.2 are diverted in a direction of a reservoir (18).

15. The fuel cell system (1) as claimed in claim 10, characterized in that the return line (21) has a shut-off valve (26), wherein the shut-off valve (26) is arranged between the recirculation blower (8) and the separator (10).

16. The fuel cell system (1) as claimed in claim 12, characterized in that a first sensor arrangement (22) and/or a second sensor arrangement (24) are connected to a control device (14), wherein the first sensor arrangement (22) continuously detects parameters of the separator (10) and the second sensor arrangement (24) continuously detects parameters of the recirculation blower (8), wherein the control device (14) controls the opening and closing of the discharge valve (44) and/or of the shut-off valve (26) on the basis of the parameters detected by the sensor arrangement (22, 24).

17. The fuel cell system (1) as claimed in claim 10, characterized in that the return line (21) has a shut-off valve (26), wherein the shut-off valve (26) is arranged between the recirculation blower (8) and the collecting vessel (31).

18. The delivery unit (3) as claimed in claim 1, characterized in that a constituent H.sub.2O and/or a constituent N.sub.2 of the gaseous medium is separated off in the recirculation blower (8), wherein the separation is performed by the centrifugal principle in the recirculation blower (8).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will be described in more detail below on the basis of the drawing.

[0021] In the drawing:

[0022] FIG. 1 is a schematic illustration of a fuel cell system according to the invention with a delivery unit and a separator,

[0023] FIG. 2 shows a schematic sectional view of the separator according to the invention,

[0024] FIG. 3 shows a perspective sectional view of the delivery unit with a recirculation blower, a jet pump and a dosing valve in a housing,

[0025] FIG. 4 shows a detail, denoted by II in FIG. 3, of a compressor space of the recirculation blower,

[0026] FIG. 5 shows a detail, denoted by III in FIG. 4, of a separation space.

DETAILED DESCRIPTION

[0027] FIG. 1 is a schematic illustration of a fuel cell system according to the invention with a delivery unit 3 and a separator 10.

[0028] Here, it is shown in FIG. 1 that the fuel cell system 1 has a fuel cell 2, wherein the fuel cell 2 has an anode region 38 and a cathode region 40. Here, the anode region 38 of the fuel cell 2 is connected to an anode circuit 9, wherein the anode circuit 9 has the separator 10, the delivery unit 3 and a tank 42. Here, the separator 10 is arranged in the anode circuit 9 upstream of the delivery unit 3 in a flow direction V, wherein the anode region 38 is fluidically connected to the separator 10 by means of a first connecting line 23, and the separator 10 is fluidically connected to the delivery unit 3 by means of a second connecting line 25, and the delivery unit 3 is fluidically connected to the anode region 38 by means of a third connecting line 27. The delivery unit 3 furthermore has a recirculation blower 8, a jet pump 4 and a dosing valve 6, wherein the dosing valve 6 is situated between the tank 42 and the jet pump 4. In one exemplary embodiment, the dosing valve 6 is connected at least approximately directly to the jet pump 4, wherein an external pipeline between the two components is either not provided, because the dosing valve 6 is formed in an integrated manner in the jet pump 4, or the external pipeline is designed to be as short as possible in order to prevent flow losses through the pipeline.

[0029] Here, the recirculation blower 8 of the delivery unit 3 delivers an unconsumed recirculate, passing from the fuel cell 2, into the jet pump 4 via a first inflow line 28. Furthermore, pressurized H.sub.2, which is in particular a motive medium, is fed in a flow direction VII to the jet pump 4 by means of the dosing valve 6 and flows into the jet pump 4 via a second inflow line 36. Furthermore, a separation of the constituent H.sub.2O and/or of the constituent N.sub.2 from the gaseous medium in the anode circuit 9 is performed by means of the recirculation blower 8 and/or by means of the separator 10. Here, the recirculation blower 8 is connected to the separator 10 by means of a return line 21. Here, a discharge of H.sub.2O and/or N.sub.2 from the recirculation blower 8 into the separator 10 may take place in a flow direction VI. Furthermore, the return line 21 has a shut-off valve 26, wherein the shut-off valve 26 is situated between the recirculation blower 8 and the separator 10, in particular a collecting vessel 31 of the separator 10. Furthermore, at the collecting vessel 31 of the separator, there is situated a discharge valve 44, by means of which the heavy constituents H.sub.2O and/or N.sub.2 that have been separated off from the gaseous medium can be discharged from the anode circuit 9 and/or from the fuel cell system 1.

[0030] Furthermore, it is shown in FIG. 1 that a first sensor arrangement 22 and/or a second sensor arrangement 24 are connected to a control device 14, wherein, in particular, the first sensor arrangement 22 continuously detects parameters of the separator 10 and the second sensor arrangement 24 continuously detects parameters of the recirculation blower 8, wherein the control device 14 controls the opening and closing of the discharge valve 44 and/or of the shut-off valve 26 in particular on the basis of the parameters detected by the sensor arrangement 22, 24. Here, the detected parameters may for example be pressure, temperature, volume flow, concentration of different constituents of the gaseous medium, such as for example H.sub.2, H.sub.2O, N.sub.2 and/or dirt particles. Here, the sensor arrangement 22, 24 may for example also be installed directly on the delivery unit 3. By means of a corresponding logic or calculation method stored on the control device 14, for example in the form of a CPU with a memory unit, a corresponding actuation and/or opening and/or closing of the valve 26, 44 can take place on the basis of the detected data such that an optimum discharge of the heavy constituents out of the anode circuit 9 and/or fuel cell system 1 can be performed, wherein the lightweight constituent H.sub.2 can be returned in the greatest possible quantity back into the anode circuit 9.

[0031] FIG. 2 shows a schematic sectional view of the separator 10 according to the invention. Here, the separator 10 has the collecting vessel 31, wherein the collecting vessel 31 is connected by means of the return line 21 and/or the first connecting line 23 and/or the second connecting line 25 to the anode circuit 9 of the fuel cell system 1 and/or various components of the fuel cell system 1, such as the recirculation blower 8. Furthermore, the collecting vessel 31 has the discharge valve 44 and/or an outflow line 32 by means of which the heavy constituents, in particular H.sub.2O and/or N.sub.2, can be discharged into the environment or returned into the cathode circuit of the fuel cell system 1. Here, the discharge valve 44 and/or the outflow line 32 is arranged for example at a low geodetic height in the collecting vessel 31, in particular in order for the heavy constituents to be conducted into and/or collected in said region of the collecting vessel 31 by means of gravitational force. Here, all of the H.sub.2O and/or N.sub.2 can be discharged out of the region of the anode circuit 9 via the discharge valve 44. The region of the low geodetic height in the collecting vessel 31 is referred to here as reservoir 18. Above the reservoir 18, on that side of the reservoir 18 which is averted from the discharge valve 44, there may be situated at least one wall which serves as an overflow guard of the reservoir 18. Here, by contrast, the second connecting line 25 may be arranged on the opposite side of the collecting vessel 31, for example at a high geodetic height of the collecting vessel 31.

[0032] It is furthermore shown in FIG. 2 that a separating edge 37 is arranged in the collecting vessel 31 such that the inflowing gaseous medium, which passes from the anode region 38 and which flows in via the first connecting line, and which is in particular a recirculate, is diverted and/or split up such that the lightweight constituent H.sub.2 is diverted in the direction of the second connecting line 25, and the heavy constituents H.sub.2O and/or N.sub.2 are diverted in the direction of a reservoir 18. Here, the effect of gravitational force on the gaseous medium is utilized, by means of which the lightweight constituents are diverted into an upper region of the separating edge 37, in particular on that side of the separating edge 37 which faces toward the second connecting line 25, and wherein the heavy constituents, owing to their greater mass, are diverted into a lower region of the separating edge 37, in particular on that side of the separating edge 37 which faces toward the reservoir 18. The splitting of the lightweight constituents from the heavy constituents is accelerated by means of the separating edge 37, because the respective constituents undergo a diversion in each case into a region of high geodetic height or into a region of low geodetic height in the collecting vessel 31. It is furthermore shown that, in one exemplary embodiment, a membrane space 33 is situated in the region of the high geodetic height in the collecting vessel 31, in particular in the region in which the collecting vessel 31 is fluidically connected to the second connecting line 25. Here, the membrane space 33 has, in particular, a membrane insert 35. The membrane insert 35 is in this case in the form of a semipermeable membrane, wherein the lightweight constituent H.sub.2 of the medium can pass through the membrane, whereas it is not possible for the constituents H.sub.2O and/or N.sub.2 to pass through the membrane, in particular owing to the molecule size. Here, the gaseous medium that is intended to pass from the collecting vessel 31 into the second connecting line 25 must pass through the membrane space 33 and/or the membrane insert 35 and/or the membrane. Furthermore, owing to the embodiment according to the invention of the separator 10, the advantage can be achieved that a stratification of the constituents of the gaseous medium in the collecting vessel 31 is achieved through the utilization of gravitational force.

[0033] It is furthermore shown in FIG. 2 that the separator 10 has the first sensor arrangement 22, wherein the first sensor arrangement 22 continuously detects parameters from the collecting vessel 31, wherein the first sensor arrangement 22 and/or the control device 14 evaluates and/or processes the detected data and/or computationally evaluates said data by means of a CPU, and wherein the discharge valve 44 is actuated by means of the control device 14. In a further exemplary embodiment, the sensor arrangement 22 may also detect the filling level of the separator 10 in the region of the reservoir 18 and use these detected data for the evaluation, in particular by means of the CPU and/or the control device 14, such that, for example, the discharge valve 44 is actuated when a certain filling level is overshot, and thus the reservoir 18 is emptied. The actuation of the discharge valve 44 by means of the control device 14 may in this case be performed mechanically and/or electrically and/or electronically and/or in some other way, wherein a complete and/or partial opening or closing of the discharge valve 44 is possible. This type of actuation furthermore applies to the shut-off valve 26 (not shown in FIG. 2) and the second sensor arrangement 24 by means of the control device 14 in a similar and/or congruent manner.

[0034] FIG. 3 shows a perspective sectional view of the delivery unit 3 with the recirculation blower 8, the jet pump 4 and the dosing valve 6. Here, it is shown that the delivery unit 3 has the recirculation blower 8 and the dosing valve 6 as further components in addition to the component of j et pump 4, wherein the flow contours of the components 4, 6, 8 for the gaseous medium and/or the components 4, 6, 8 are arranged at least approximately entirely in a common housing 7. Here, in one exemplary embodiment, the housing may be formed in two parts, three parts or more parts. Here, the individual parts are in particular composed of the same material, and/or have an at least approximately equal coefficient of thermal expansion. Here, the recirculation blower 8 has a drive 47, in particular an electric drive 47, which, by means of a drive shaft, is at least cardanically connected to a compressor wheel 12 which is rotatable about an axis of rotation 48. When a torque is transmitted from the drive 47 to the compressor wheel 12, the compressor wheel 12 is set in rotational motion, and the at least one delivery cell 20 moves, in circulating fashion about the axis of rotation 48, through a compressor space 30 in the housing 7. Here, in each case always one of the delivery cells 20 is arranged between two blades 5 of the compressor wheel 12. Here, a gaseous medium already situated in the compressor space 30 is moved concomitantly, and in the process delivered and/or compressed, by the at least one delivery cell 20. Furthermore, a movement of the gaseous medium, in particular a flow exchange, takes place between the at least one delivery cell 20 and the at least one side channel 19. Here, for the delivery action, it is crucial that, during operation, a circulating flow can form within the at least one side channel 19.

[0035] By means of the second inflow line 36, a pressurized motive medium is fed to the dosing valve 6, which motive medium is fed via a nozzle to an intake region 11 by means of opening and closing of the dosing valve 6 and, there, merges with the recirculate passing from the recirculation blower 8. Here, the jet pump 4, in a flow direction VIII that runs in particular along its longitudinal axis 50, has the intake region 11, a mixing pipe 13 and a conically running diffuser region 15 and an outlet manifold 17, wherein the latter is connected to the third connecting line 27. Here, a so-called jet pump effect occurs within the jet pump 4. For this purpose, the gaseous motive medium, in particular H.sub.2, flows into the dosing valve 6 from the outside, in particular from the tank 42, through the second inflow line 36. The motive medium is then introduced, in particular at high pressure, into the intake region 11 by means of an opening of the dosing valve 6. Here, the gaseous motive medium flows in the direction of the flow direction VIII. The H.sub.2 which flows from the second inflow line 36 into the intake region 11 and which serves as motive medium has a pressure difference in relation to the recirculation medium that flows from the first inflow line 28 into the intake region 11, wherein the motive medium is in particular at a relatively high pressure of at least 10 bar. In order that the jet pump effect occurs, the recirculation medium is delivered with a low pressure and a small mass flow into the intake region 11 of the jet pump 4. Here, the motive medium flows with the described pressure difference and a high speed, which is in particular close to the speed of sound, through the dosing valve 6 into the intake region 11. Here, the motive medium impinges on the recirculation medium that is already situated in the intake region 11. Owing to the high speed and/or pressure difference between the motive medium and the recirculation medium, internal friction and turbulence are generated between the media. Here, a shear stress arises in the boundary layer between the fast motive medium and the much slower recirculation medium. This stress gives rise to a transfer of momentum, wherein the recirculation medium is accelerated and entrained. The mixing occurs in accordance with the principle of conservation of momentum. Here, the recirculation medium is accelerated in the flow direction VI and a pressure drop also occurs for the recirculation medium, whereby a suction effect occurs and thus a follow-up delivery of further recirculation medium out of the region of the first inflow line 28 and/or of the recirculation blower occurs. By means of a change and/or regulation of the opening duration and of the opening frequency of the dosing valve 6, a delivery rate of the recirculation medium can be regulated and adapted to the respective requirement of the fuel cell system 1 as a whole in a manner dependent on the operating state and operating requirements.

[0036] It is furthermore shown in FIG. 3 that the components 4, 6, 8 of the delivery unit 3 are each arranged in a compact manner with respect to one another in the housing 7. Here, the recirculation blower 8 and the jet pump 4 are arranged relative to one another in the common housing 7 such that the axis of rotation 48 of the compressor wheel 12 of the recirculation blower 8 runs at least approximately perpendicular to the longitudinal axis 50 of the jet pump 4. In this way, it is possible on the one hand for the surface area of the delivery unit 3 and/or the required structural space in the vehicle to be reduced. On the other hand, the flow contours of the components 4, 6, 8 can be arranged in a space-saving manner with respect to one another such that, for example, a gas outlet opening 16 of the recirculation blower 8 can flow approximately directly into the intake region 11 and/or the first inflow line 28 of the jet pump 4, in particular via an integrated flow channel 41 which is optimized in terms of flow and which has a curvature 43, wherein a diversion and/or flow guidance of the gaseous medium between the recirculation blower 8 and the jet pump 4 takes place exclusively in the region of the curvature 43. It is thus the case that at least approximately no additional pipelines are required for connecting the components 4, 6, 8. Furthermore, the second sensor 24 and/or a low-pressure sensor 45 are arranged in a space-saving and/or integrated manner in the housing 7, whereby less structural space is required.

[0037] The drive 47, which is composed in particular of a thermally conductive material, can be advantageously warmed up, which is advantageous in particular during a cold-start procedure of the delivery unit 3 and/or of the vehicle. Here, the drive 47 warms up and, for example owing to its thermal conductivity, transfers the thermal energy to the compressor wheel 12 and further components of the delivery unit 3 and/or the housing 7. Upon a shutdown of the delivery unit 3 and/or of the vehicle, in particular over a relatively long period of time and/or in the presence of low ambient temperatures below the freezing point, the liquid freezes, and ice bridges form. These ice bridges can, upon a start-up and/or upon starting and/or during operation, lead to damage to the delivery unit 3 and/or of the fuel cell system 1. As a result of the heating of the drive 47, the ice bridges melt, and the liquid changes from a solid to a liquid state of aggregation and can be discharged. Here, the arrangement of the drive 47 is such that the introduction of heat into the housing 7 takes place as quickly and efficiently as possible. Here, a specific form of the integrated housing, and the use of composite material for the housing, can lead to improved thermal conductivity. Alternatively, in one exemplary embodiment, the use of thermal effects from the fuel cell 2, in particular a stack, can be used for warming or cooling the integrated housing 7. Furthermore, the actuator arrangement of the dosing valve 6 can be used as heat source, and advantageously acts similarly to the drive 47.

[0038] FIG. 4 shows a detail, denoted by II in FIG. 3, of the compressor space 30 of the recirculation blower 8 with the compressor wheel 12. It is shown here that the compressor wheel 12 has an encircling outer delimiting ring 39 which runs rotationally symmetrically with respect to the axis of rotation 48 of the compressor wheel 12. Here, a separation space 34 which is at least partially encapsulated, in particular with respect to the at least one side channel 19, and/or a discharge channel 46, is situated in the housing 7 of the recirculation blower and/or of the delivery unit 3 on that side of the compressor wheel 12 which is averted from the axis of rotation 48. The compressor wheel 12 is furthermore of symmetrical construction in relation to an axis of symmetry 49, wherein the axis of symmetry 49 runs orthogonally with respect to the axis of rotation 48.

[0039] Furthermore, the trailing contour of a blade 5 of the compressor wheel 12 is shown, wherein this contour is merged in another section along the axis of symmetry 49.

[0040] Here, the compressor wheel 12 is shown, which, in the region of the outer delimiting ring 39, has at least one externally situated encircling annular collar 29a, b. Said externally situated annular collar 29a, b runs axially in relation to the axis of symmetry 49 and on that side of the outer delimiting ring 39 which is averted from the axis of rotation 48. Here, the at least one externally situated annular collar 29a, b is, axially and/or radially in relation to the axis of symmetry 49, at least approximately in contact with the housing upper part 7 and/or the housing lower part 8 of the housing 7 and/or forms a small gap therewith, which at least approximately cannot be overcome by the gaseous medium. By virtue of the fact that a small gap can form between the compressor wheel 12 with the at least one externally situated encircling annular collar 29a, b and the housing 7, an at least partial encapsulation of the at least one side channel 19 with respect to the separation space 34 can be realized.

[0041] It is furthermore illustrated in FIG. 4 that the separation space 34 is formed, at least partially in encircling fashion about the axis of rotation 48, between the housing 7 and the outer delimiting ring 39. The heavy constituents are thus discharged out of the region of the at least one side channel 19 and of the delivery cell 20 and collected in the region of the separation space 34. These heavy constituents of the gaseous medium may for example be an undesired waste product and/or by-products from the operation of the fuel cell system 1. As a result of the discharge of the heavy constituents, the delivery and compression action of the delivery unit 3 can be increased, because the fraction of the gaseous medium to be delivered, in particular H.sub.2, which is required for the generation of electricity in the fuel cell 2, in the delivery cell 20 and the at least one side channel 19 is increased. In this way, the efficiency of the delivery unit 3 can be increased, because no heavy constituents, which are undesired for operation, have to be delivered concomitantly.

[0042] FIG. 5 shows the detail of the separation space 34 that is denoted by III in FIG. 4. It is illustrated here that the constituent H.sub.2O and/or the constituent N.sub.2 is separated off from the gaseous medium in the recirculation blower 8, wherein the separation takes place in particular by means of the centrifugal principle in the recirculation blower 8. It is shown here that the separation space 34 is at least indirectly fluidically connected via the discharge channel 46 to the recirculation line 21, wherein the recirculation line 21 fluidically connects the delivery unit 3 and/or the recirculation blower 8 at least indirectly to the collecting vessel 31 of the separator 10. Here, the separation space 34 and/or the discharge channel 46 can form an elevated pressure level in relation to the collecting vessel 31 of the separator 10, and wherein a discharge of H.sub.2O and/or N.sub.2 from the recirculation blower 8 into the separator 10 takes place in the flow direction VI.

[0043] Through the formation of this separation space 34, it is possible for the heavy constituents to be discharged from the gaseous medium, in particular N.sub.2 and/or H.sub.2O, and collected in said separation space 34. Here, a rotation of the compressor wheel 12 during operation is advantageously utilized to utilize a greater centrifugal force of the heavy constituents owing to the higher mass in relation to the rest of the gaseous medium, in particular H.sub.2, to achieve that the heavy constituents are moved away from the axis of rotation 48 by means of the centrifugal force with such intensity that they move in a flow direction IX from the at least one side channel 19 between the compressor wheel 12 and the housing 7, in particular in the region of the small gap, into the separation space 34, wherein a separation based on centrifugal force occurs. The additional discharge channel 46 is advantageously situated at the geodetic lowest point of the separation space 34. It is advantageous here that, by means of the action of gravitational force and/or centrifugal force on the heavy constituents of the gaseous medium that have collected in the separation space 34, an automatic discharge through the discharge channel 46 into the return line 21 occurs without the need for further measures, for example mechanical pumped discharge. Furthermore, the effect of the automatic discharge of the heavy constituents through the discharge channel 46 to the outside is intensified in that, during the operation of the recirculation blower 8, heavy constituents continue to flow into the separation space 34 and thus force the heavy constituents already situated there out through the discharge channel 46.

[0044] This furthermore offers the advantage that the heavy constituents can, on the one hand, be discharged out of the region of the delivery cell 20 and/or the at least one side channel 19 and, on the other hand, can also be discharged out of the region of the separation space 34, and out of the delivery unit 3, via the discharge channel 46. In this way, the risk of damage to the rotating components, in particular to the compressor wheel or to bearings thereof, is prevented, because remaining heavy constituents, such as for example H.sub.2O, lead to formation of ice bridges in the shut-down state of the fuel cell system 1 and in the presence of low ambient temperatures, which ice bridges can damage said components upon starting of the recirculation blower 8. This damage is prevented by way of the discharge of the heavy constituents via the discharge channel 46. Furthermore, the advantage is achieved that, as a result of the heavy constituents being conducted out, a formation of so-called ice bridges between the moving parts, in particular the compressor wheel 12 and the housing 7, in the shut-down state of the fuel cell system 1 and in the presence of low ambient temperatures is prevented.

[0045] The invention is not restricted to the exemplary embodiments described here and to the aspects highlighted therein. Rather, within the scope specified by the claims, a large number of modifications are possible which lie within the abilities of a person skilled in the art.