DEVICE FOR ANODE GAS RECIRCULATION IN A FUEL CELL SYSTEM

Description

[0001] The invention relates to a device for anode gas recirculation in a fuel cell system comprising a blower with an impeller and a conveying channel extending from a conveying channel inlet to a conveying channel outlet, and an electric motor with a drive shaft on which the impeller is mounted.

[0002] Fuel cell systems convert the chemical reaction energy of a continuously supplied fuel, particularly hydrogen, and an oxidizing agent, usually oxygen, into electrical energy, which can be used, for example, as propulsion energy for vehicles. The hydrogen path of a low-temperature fuel cell, as commonly used in vehicles, essentially consists of the supply line for pure hydrogen via a pressure-reducing and metering valve, the actual fuel cell unit, and a recirculation path that forms a gas-tight connection between the outlet of the fuel cell unit and its inlet, i.e., the hydrogen supply line. The resulting circuit is called the anode gas recirculation circuit.This anode gas recirculation circuit is necessary to prevent unused hydrogen from being released into the atmosphere. This occurs because the fuel cell unit is supplied with fresh hydrogen at a superstoichiometric level. Thus, the anode gas circuit is designed as a closed circuit, and the unused hydrogen is recirculated into the supply line downstream of the hydrogen metering unit by means of a recirculation blower. Such blowers are designed, for example, as side-channel blowers. These blowers are typically driven by electric motors, which, when operated in vehicles, are powered by the vehicle battery. The problem with these drives is the high heat generation of the electronic components and the stator windings.

[0003] In addition to the unused hydrogen, the recirculated anode gas consists of nitrogen, which comes from the fresh air of the fuel cell unit, and water vapor. Liquid product water is also present at the fuel cell unit outlet, which is also conveyed by the recirculation fan.

[0004] To remove the water from the gas mixture, it is necessary to remove the product water and, if possible, condense the water vapor. Condensers are used for this purpose.

[0005] To solve these problems, DE 10 2012 221 445 A1 proposes an anode gas recirculation blower with a condenser located on the rear side of an electric motor of the blower, whose condensate is discharged into a cooling channel surrounding the electric motor. A similar anode gas recirculation blower is known from DE 10 2019 003 386 A1. However, it has been shown that the amount of water generated from the anode gas stream is often insufficient to reliably cool the electric motor.

[0006] From DE 10 2019 215 473 A1 it is known to provide a centrifuge separator on the inlet side.

[0007] The task therefore arises of providing a device for anode gas recirculation in a fuel cell system that, on the one hand, ensures sufficient removal of water from the anode gas circuit and, on the other hand, reliably prevents overheating of the electric motor. These functions should require as little installation space as possible.

[0008] This object is achieved by a device for anode gas recirculation in a fuel cell system having the features of main claim 1.

[0009] The inventive device for anode gas recirculation in a fuel cell system comprises a blower whose impeller is rotatably arranged in a conveying channel, so that the anode gas is conveyed by the impeller from a conveying channel inlet to a conveying channel outlet. The impeller is driven by an electric motor that drives a drive shaft on which the impeller is mounted. According to the invention, the blower comprises a cooling channel through which the anode gas flows, which at least partially surrounds the electric motor of the blower. The anode gas can be either drawn or pushed through the cooling channel, depending on whether the cooling channel is arranged fluidically upstream or downstream of the conveying channel of the blower. The conveying channel is further delimited by a radially outer wall, which ensures the flow around the electric motor.The cooling channel is designed or serves as a droplet separator, with the resulting droplets being drained away via a condensate drain channel. The cooling channel can be designed as a droplet separator in various ways. In any case, the cooling channel must contain internal fittings that force the gas flow to divert. Accordingly, advantage is taken of the fact that the temperature of the anode gas flow is usually below 100°C, making it suitable for cooling the electronics and stator of the electric motor. At the same time, however, the cooling channel can be used as a condenser by providing appropriate internal fittings or by guiding the anode gas in a spiral around the electric motor at sufficient speed. In both cases, the water is separated from the internal fittings or the outer wall due to its higher inertia compared to the gas and can then be drained away via a condensate drain.Thus, the cooling and condensation functions are realized in the cooling channel in a very small space and in a single process step. The use of separate coolant is also completely eliminated.

[0010] Preferably, the cooling channel is located upstream of the discharge channel so that water does not enter the discharge channel. This prevents damage to the impeller blades and reduces wear accordingly. Furthermore, corrosion can be reduced.

[0011] Preferably, the fan impeller is positioned entirely above or below the electric motor, and the shaft is aligned in the direction of the gravitational force acting upon it. The fan is thus vertically oriented. The condensate is discharged at one of the axial ends, so that the flow through the cooling channel remains unchanged and, in particular, the water in the anode gas stream can still be used for cooling over its entire circumference. If the impeller is positioned below the electric motor, condensate can also be drained from the area of ​​the conveying channel at the same position. Flow through the cooling channel can flow from the rear of the fan to the front, i.e., toward the impeller, or vice versa.

[0012] Throughout the entire disclosure of this document, it is noted that the terms above, below, under, above, downward, or upward each refer to an installation direction in which the fan is installed, for example, in a vehicle. It is always assumed that the earth's center of gravity serves as a reference point for the fan. Accordingly, the terms always refer to the direction of the acting gravitational force, assuming, for example, that the vehicle is on a straight plane aligned perpendicular to the direction of gravity. Therefore, if a first element is arranged above a second element, this means that this first element is arranged further away from the earth's center of gravity than the second element.

[0013] Furthermore, it is advantageous if a wall bordering the cooling channel at the bottom is inclined toward an opening that forms an inlet for the condensate drain channel. In this way, all the water dripping down the walls is safely guided into the opening and thus to the condensate drain by the force of gravity.

[0014] In a preferred embodiment, the inlet of the condensate drain channel is located in the downwardly delimiting wall on the radially outer region opposite the radially outer wall, since the majority of the water will settle on this outer wall and drain down there. This is due, on the one hand, to the fact that the outer wall is usually colder than the inner wall and, on the other hand, to the flow of the anode gas, which usually circulates at least partially around the electric motor, thus forcing the heavier water droplets outward against the radially delimiting wall. This ensures that the separated water is drained from the cooling channel as quickly and completely as possible.

[0015] In another design, the condensate drain outlet is located at the lower end of the fan, below the conveying channel. This prevents condensate from flowing back toward the conveying channel.

[0016] Preferably, an anode gas outlet of the cooling channel opens directly into a conveying channel inlet. Accordingly, the anode gas or the water-reduced anode gas flows through the cooling channel and then the conveying channel, minimizing the conveying path between the conveying channel and the cooling channel.

[0017] Additionally, it is advantageous if the anode gas outlet of the cooling channel is axially offset from the condensate drain channel and positioned above the condensate drain channel. With such an arrangement, the condensate typically collects below the anode gas outlet of the cooling channel to reach the condensate drain channel and thus does not typically flow into the conveying channel against the force of gravity.

[0018] In a further embodiment, the anode gas outlet of the cooling channel is arranged above the conveying channel and is offset radially inward from a radially outwardly bounding wall, and is radially spaced from the radially outwardly bounding wall. This means that the condensate flowing along the radially outer wall does not reach the anode gas outlet of the cooling channel, since the wall does not directly open into the anode gas outlet due to the radial distance.

[0019] If the fan is installed in a position where the conveying channel is located above the electric motor, the anode gas outlet of the cooling channel can preferably be located below the conveying channel, and the condensate drain channel can be located on the axially opposite side of the fan, i.e., at the lower end. This has the advantage that the gas is conveyed in the opposite direction to the gravitational force acting on the liquid, thereby almost completely preventing the entrainment of the deposited water droplets.

[0020] In a further embodiment, the cooling channel opens below the conveying channel into a space into which a pipe protrudes from above, forming the anode gas outlet of the cooling channel. The condensate drain is located at the lower end of the space. Due to the expansion of the space available for the anode gas, additional water is separated, which collects in the lower space due to gravity and can drain away, while the gas is discharged upward through the pipe, similar to a cyclone separator. This makes it easy to achieve a good separation efficiency directly at the blower.

[0021] In a further development, the anode gas outlet is fluidly connected to the conveying channel inlet, and the conveying channel is positioned above the chamber, allowing the anode gas, freed from water, to flow directly from the chamber into the conveying channel. This ensures cooling, condensation, and conveying within the smallest possible space.

[0022] In a particularly preferred embodiment of the invention, the cooling channel surrounds the electric motor in a spiral shape. Accordingly, separation takes place in the form of a centrifugal separator. To achieve this, the cooling channel must not be designed with an excessively large cross-section, but a sufficient flow velocity must be ensured within the cooling channel. If this is the case, the heavier water droplets are accelerated against the outer wall and flow down the wall to the condensate drain channel.

[0023] In a further embodiment, the radially outer wall of the helical cooling channel is smooth. This minimizes the flow resistance for the anode gas flow and ensures smooth drainage of the condensate along this wall.

[0024] In a further advantageous embodiment, the cooling channel is helically flowed from top to bottom, and the conveying channel is arranged above the electric motor and connected to the conveying channel inlet via a connecting channel, at the upstream end of which the condensate drain channel is formed. This way, the water collects in the end region of the cooling channel at the lower end. While the anode gas flow is subsequently conveyed upward to the conveying channel, the condensate can be discharged at the bottom, again preventing entrainment. This design also achieves an effect similar to that of a cyclone separator, with the connecting channel acting as the dip tube. This also achieves a very good separation and cooling effect.

[0025] In an alternative embodiment, baffles are arranged in the cooling channel, which are aligned at an angle of 45° to 135° to the main flow direction. The moist gas is guided through the baffles, which deflect the flow direction of the gas several times. The liquid droplets cannot follow these changes in direction, which is why they impact the internals and settle there. As the droplets become increasingly deposited, they flow downwards. The droplets can be collected in the lower area and then discharged via the condensate drain channel. This simply uses the cooling channel as a droplet separator. The baffles can be designed as solid walls or as grid walls. They can be formed on either the inner or outer wall of the cooling channel and can completely or partially close off the flow path across either an axial or a radial cross-sectional area.

[0026] In a further embodiment, a baffle wall is formed upstream of the anode gas outlet of the cooling channel, which, viewed in the circumferential direction, conceals the anode gas outlet. This ensures that the anode gas flow encounters a deflection before the outlet and that any remaining droplets are separated.

[0027] Thus, a device for anode gas recirculation in a fuel cell system is created which requires little installation space and at the same time realizes cooling of the drive motor and water separation from the anode gas stream.

[0028] Two embodiments of the invention are illustrated in the figures and are described below. Figure 1 shows a perspective view of a first embodiment of a blower of a device according to the invention for anode gas recirculation in a fuel cell system. Figure 2shows a perspective view of the fan from Figure 1 with outer casing part cut away. Figure 3 shows a head view of the blower from Figure 1 in cut representation. Figure 4 shows a side view of a second device according to the invention for anode gas recirculation in a fuel cell system in a schematic representation. Figure 5 shows a side view of a third device according to the invention for anode gas recirculation in a fuel cell system in a schematic representation.

[0029] The Figures 1 to 3The blower 10 shown has an outer motor housing part 12 which radially surrounds an inner motor housing part 13, in which an electric motor 14 is arranged, which drives an impeller 16, via which an anode gas is conveyed via a conveying channel 18 which is at least partially formed in a blower head housing 20. The outer motor housing part 12 is fastened to the blower head housing 20 and closed on the axial side opposite the blower head housing 20 by a cover 22, behind which the electronics 23 of the electric motor 14 are arranged, which, like windings 24 of a stator 26, are connected to a voltage source via a plug 28. The stator 26 corresponds in a known manner to a permanent magnet rotor 30, which is fixedly fastened to a drive shaft 32, to which the impeller 16 is in turn fastened.

[0030] In the present embodiment, a flange 34 is formed on the blower head housing 20, on which a conveying channel outlet 36 is formed, which is fluidically connected to the conveying channel 18. Furthermore, an anode gas inlet 38 is formed on the outer housing part 12, which leads into a cooling channel 40 formed between the inner motor housing part 13 and the outer motor housing part 12 and at least partially surrounding the electric motor 14. The cooling channel 40 serves to dissipate heat from the electric motor 14 and is delimited radially outwardly by a radially outer wall 42, which is formed by an inner wall of the outer motor housing part 12.

[0031] Baffles 44 are formed in the cooling channel 40, extending axially from the top and bottom into the cooling channel 40, thereby continuously forcing a flow reversal in the cooling channel 40. The baffles 44 serve as internals of a droplet separator 46, since water present in the anode gas stream as droplets or water vapor, due to its greater inertia compared to the nitrogen and hydrogen present in the anode gas stream, collides with the baffles 44, collects, and slides down due to gravitational force, particularly on the radially outer wall 42, which is colder and in the direction of which the droplets are carried by centrifugal force.A wall 48 axially delimiting the cooling channel 40 downwards is formed at an angle to an opening 50, so that the drops collecting on this wall 48 slide to this opening 50, which serves as an inlet 52 of a condensate drainage channel 54 extending from the inner motor housing part 13 through the fan head housing 20 to an outlet 56. The wall 48 is formed sloping both horizontally and radially outwardly toward the opening 50, which borders the surrounding radially outer wall 42, so that the water flows to the opening 50 due to gravity.

[0032] An anode gas outlet 58, through which the water-reduced anode gas flows from the cooling channel 40, is arranged axially slightly higher than the inlet 52 of the condensate drain channel 54 to prevent water from flowing to the anode gas outlet 58. In addition, the anode gas outlet 58 is arranged directly in the flow shadow of a final baffle 44, through which water is separated again immediately upstream of the anode gas outlet 58. Furthermore, the anode gas outlet 58 is arranged in a radially inner region of the cooling channel 40, thus having a radial distance from the radially outer wall 42, so that the more inert water would also have to be transported inwards and thus against the centrifugal force and the outwards acceleration caused by the baffle 44 in order to reach the anode gas outlet 58 of the cooling channel 40.

[0033] The anode gas outlet opens directly into, or forms, a conveying channel inlet 60, through which the at least partially dried anode gas flows into the conveying channel 18, where it is compressed and flows to the conveying channel outlet 36, which is fluidly connected to a fuel cell stack, while the recovered condensate flows via the condensate drain channel 54 to the outlet 56. This simultaneously cools the electric motor 14 and separates the process water from the anode gas stream.

[0034] An alternative design of such a combined cooling and water separation is shown schematically in the Figure 4 shown, whereby the same reference symbols are used below for the same components.

[0035] The droplet separator 46 used here acts as a cyclone separator in that the cooling channel 40 is designed in a helical shape, in which a sufficiently high flow velocity is achieved to separate the heavier water droplets and water vapor from the remaining anode gas flow due to the existing centrifugal force. Due to its higher inertia, it is accelerated outwards against the radially outer wall 42. This wall 42 is smooth, so that the water droplets striking this also colder wall 42 slide down again due to the acting gravitational force. In the lower area, the water and the anode gas flow separated in this way reach a chamber 62 in which expansion also occurs due to the cross-sectional expansion, which can lead to an additional temperature loss and thus to additional water droplets being formed.In any case, the water already separated reaches the condensate drain channel 54 via the axially limiting funnel-shaped and thus inclined wall 48, while the anode gas reaches the feed channel 18 via a pipe 64 immersed in the space 62, which serves as anode gas outlet 58 of the cooling channel 40, where it is compressed again and pumped towards the fuel cell.

[0036] In the Figure 5An alternative embodiment is shown in which, in contrast to the previous embodiments, the conveying channel 18 is this time arranged above the electric motor 14, so that in this case the force of gravity removes a liquid from the conveying channel 18. The anode gas inlet 38 into the cooling channel 40 is in the upper region of the fan 10. From here, the anode gas enters a helical cooling channel 40 corresponding to the previously described embodiment, so that the water again settles on the radially outer wall. From there, in the present embodiment, it flows directly into the adjoining condensate drain channel 54. However, the dried anode gas can be conveyed towards the conveying channel 18 following the pressure gradient via a connecting channel 66, which forms the anode gas outlet 58 of the cooling channel 40.The separation of water and water vapor from the anode gas stream occurs through centrifugal forces and the removal through gravitational force.

[0037] In all three cases, the anode gas from the recirculation path is used directly to cool the electric motor driving the fan, while water is continuously removed from this gas. This reduces the required installation space and integrates two system functions into one component, thus reducing costs. Of course, a valve should be installed downstream of the condensate drain channel to drain the accumulating condensate and prevent anode gas from flowing into the condensate drain channel.

[0038] It should be clear that the described device for anode gas recirculation in a fuel cell system is not limited to the described embodiments. Furthermore, if the blower is a side-channel blower, a second condensate drain can be formed at its lowest point in the conveying channel and, viewed in the direction of rotation of the impeller, immediately upstream of an interrupter section of the conveying channel, through which residual moisture entering the conveying channel can also be separated. Various mist eliminators can also be used, or the various discharges of the separated substances shown can be combined in different ways with the various separation options.

Claims

1. Device for anode gas recirculation in a fuel cell system, comprising a fan (10) with a wheel (16) and a delivery duct (18) which extends from a delivery duct inlet (60) to a delivery duct outlet (36), and an electric motor (14) with a drive shaft (32) on which the impeller (16) is fastened, wherein the fan (10) has a cooling duct (40) through which the anode gas flows and which at least partially surrounds the electric motor (14) of the fan (10), is delimited by a radially outer wall (42), characterized in that the cooling duct is formed as a droplet separator (46) by internals which lead to a forced deflection of the gas flow, wherein the droplets can be discharged via a condensate discharge duct (54).

2. Device for anode gas recirculation in a fuel cell system according to claim 1, characterized in that the cooling duct (40) is arranged upstream of the delivery duct (18).

3. Device for anode gas recirculation in a fuel cell system according to claim 1 or 2, characterized in that the wheel (16) of the fan (10) is arranged completely above or below the electric motor (14) and the drive shaft (32) is oriented in the installed state in the direction of the acting gravitational force.

4. Device for anode gas recirculation in a fuel cell system according to one of the preceding claims, characterized in that a wall (48) which delimits the cooling duct (40) at the bottom is formed so as to be inclined with respect to an opening (50) which defines an inlet (52) of the condensate discharge duct (54).

5. Device for anode gas recirculation in a fuel cell system according to claim 4, characterized in that the inlet (52) of the condensate discharge duct (54) is arranged in the downwardly delimiting wall (48) at the radially outer region opposite the radially outer wall (42).

6. Device for anode gas recirculation in a fuel cell system according to one of the preceding claims, characterized in that an outlet (56) of the condensate discharge duct (54) is arranged at the lower end of the fan (10) below the delivery duct (18).

7. Device for anode gas recirculation in a fuel cell system according to one of the preceding claims, characterized in that an anode gas outlet (58) of the cooling duct (40) opens directly into the delivery duct inlet (60).

8. Device for anode gas recirculation in a fuel cell system according to claim 7, characterized in that the anode gas outlet (58) of the cooling duct (40) is arranged axially offset with respect to the inlet (52) of the condensate discharge duct (54) and above the inlet (52) of the condensate discharge duct (54).

9. Device for anode gas recirculation in a fuel cell system according to claim 7 or 8, characterized in that the anode gas outlet (58) of the cooling duct (40) is arranged above the delivery duct (18) and radially inwardly offset with respect to the radially outer wall (42) and is at a radial distance from the radially outer wall (42).

10. Device for anode gas recirculation in a fuel cell system according to claim 7, characterized in that the anode gas outlet (58) of the cooling duct (40) is arranged below the delivery duct (18) and the condensate discharge duct (54) is formed on the axially opposite side of the fan (10).

11. Device for anode gas recirculation in a fuel cell system according to one of claims 1 to 6, characterized in that the cooling duct (40) opens below the delivery duct (18) into a space (62) into which a pipe (64) which defines the anode gas outlet (58) of the cooling duct (40) projects from above, wherein the inlet (52) of the condensate discharge duct (54) is provided at the lower end of the space (62).

12. Device for anode gas recirculation in a fuel cell system according to claim 11, characterized in that the anode gas outlet (58) is fluidically connected to the delivery duct inlet (60) and the delivery duct (18) is provided above the space (62).

13. Device for anode gas recirculation in a fuel cell system according to one of the preceding claims, characterized in that the cooling duct (40) surrounds the electric motor (14) in a helical manner.

14. Device for anode gas recirculation in a fuel cell system according to claim 13, characterized in that the radially outer wall (42) of the helical cooling duct (40) is provided to be smooth.

15. Device for anode gas recirculation in a fuel cell system according to claim 13 or 14, characterized in that the cooling duct (40) is flowed through in a helical manner from top to bottom and the delivery duct (18) is arranged above the electric motor (14) and is connected via a connecting duct (66) to the delivery duct inlet (60), at the upstream end of which the condensate discharge duct (54) is provided.