Fuel cell system

Abstract

The invention relates to a fuel cell system consisting of at least - a fuel cell (12), - a coolant circuit (16) having a coolant pump (18) and a heat exchanger (20), - a water separator (34), and - a fan (22), which generates a gaseous medium flow, in particular an air flow, in the direction of the heat exchanger (20), wherein by means of a cooling device, which has a conveying device (46), the water separated in the water separator (34) reaches a discharge device (50) which, by means of spray nozzles (52), sprays the water into the environment, characterised in that by means of the spray nozzles (52), the discharge device (50) sprays the water in a direction opposite the direction of the medium flow generated by the fan (22).

Description

[0001] Fuel cell system

[0002] The invention relates to a fuel cell system comprising at least one fuel cell, a coolant circuit with a coolant pump and a heat exchanger, a water separation device, a fan which generates a gaseous medium flow, in particular an air flow, through the heat exchanger, wherein by means of a cooling device which has a conveying device, the water separated by means of the water separation device reaches a discharge device which sprays the water into the environment by means of spray nozzles.

[0003] A fuel cell is a device for converting chemical energy into electrical energy from a gaseous energy carrier, such as hydrogen, and a gaseous oxidant, for example in the form of ambient air. Typically, several fuel cells are combined in a fuel cell stack to generate the desired power. Stacks of 200 or more individual cells are not uncommon. The fuel cell stack contains a cathode reactant gas, usually a flow of air, which is forced through the stack via a compressor. Not all of the oxygen is consumed by the stack, and some of the air is exhausted as a cathode exhaust gas, which may include liquid water and / or water vapor as a stack byproduct.The fuel cell stack also accommodates an anode hydrogen reactant gas, which flows into the anode side of the stack. Furthermore, flow channels are provided for a cooling fluid, which flows through the fuel cell stack to maintain thermal equilibrium. Proton exchange membranes are often used for fuel cells.

[0004] To achieve efficient stack operation and a long stack lifespan, it is necessary to operate the respective fuel cell at an optimal relative humidity and within an optimal temperature range. A typical stack operating temperature is regularly between 60°C and 80°C. The stack temperature determines the relative humidity in the fuel cells in the stack for a specific stack pressure. Stack temperatures too high above the optimal temperature can damage fuel cell components, reducing fuel cell lifespan. Stack temperatures below the optimal operating temperature also reduce stack performance. Therefore, fuel cell systems use thermal subsystems that can control the temperature in the fuel cell stack.

[0005] Such a thermal subsystem is shown in DE 10 2006 048 187 B4. The known solution relates to a fuel cell system for a vehicle, the system comprising: a fuel cell stack providing a cathode discharge on a cathode discharge line, the cathode discharge comprising gaseous and liquid water; a liquid water separator receiving the cathode discharge from the cathode discharge line and separating liquid water therefrom; and a thermal subsystem with a pump, a coolant circuit, and a cooler, the pump pumping a cooling fluid through the coolant circuit, the cooler, and the fuel cell stack, the cooler comprising a selectively permeable wall section allowing water in the cooling fluid flowing through the cooler to permeate and be evaporated on an outer surface of the wall section.and wherein the thermal subsystem further comprises a coolant reservoir to which the liquid water separated from the cathode discharge by the water separator is supplied, and from which the separated water is passed, as needed, into the coolant circuit to maintain its water supply.;

[0006] The selectively permeable wall section in the known solution comprises a cross-linked polyvinyl alcohol on a polyethersulfone carrier or has a cross-linked chitosan membrane, which can become clogged with contaminants in harsh everyday use, especially in vehicle operation, rendering them unusable. These selectively permeable carrier or membrane solutions for the heat exchanger are also relatively expensive to implement.

[0007] DE 10 2008 029 529 A1 discloses a method for operating a fuel cell system in a motor vehicle, which has at least one fuel cell from which exhaust gas containing water is emitted during operation, wherein a cooling circuit system is provided in the motor vehicle, in which a cooling fluid is conducted to a heat source in order to absorb heat there, wherein the cooling fluid is conducted to a cooling region in which the cooling fluid releases the absorbed heat to the ambient air via walls, wherein the method comprises the step of collecting water from the exhaust gas, in particular after separation, in a container, and wherein the water collected in the container is at least partially applied to the outside of the walls in the cooling region.Typically, the cooling area is designed as a radiator, preferably a finned radiator, and when the vehicle is moving, the airflow promotes the removal of water droplets from the radiator, which is simply carried along in the airflow. However, in the known solution, the airflow also promotes the evaporation of the water droplets, thus enabling cooling of the radiator and thus the cooling fluid contained therein.

[0008] Based on this state of the art, the object of the invention is to create an alternative solution that is cost-effective to implement and functionally reliable in use as well as leading to further improved cooling results.

[0009] A fuel cell system having the features of patent claim 1 in its entirety solves this problem.

[0010] Because, according to the characterizing part of patent claim 1, the discharge device sprays the water by means of spray nozzles in a direction opposite to the direction of the medium flow generated by the fan, technically complex, selectively permeable wall sections, such as cross-linked chitosan membranes, can be dispensed with, which helps reduce manufacturing costs and increases the functional reliability of the fuel cell system during operation. In particular, the solution according to the invention is insensitive to environmental contamination. Due to the electrical efficiency of the fuel cell, which can be estimated at approximately 50%, it is clear that a large proportion of the supplied energy must be dissipated as heat. This leads to the requirement for large cooling systems, particularly in low-temperature fuel cells, since the temperature difference between the ambient air and the required fuel cell temperature is only small.With the fuel cell system according to the invention, including the cooling device, such small temperature differences in low-temperature fuel cells can be reliably controlled with minimal equipment complexity. The fact that the water is sprayed by the spray nozzles in a direction opposite to the direction of the medium flow generated by the fan enables an adiabatic cooling process in a particularly advantageous manner. In this way, the water droplets emitted by the spray nozzles can be immediately atomized into a gaseous state, so that this associated adiabatic change of state from "liquid" to "gaseous" allows large amounts of heat to be dissipated from the system, significantly increasing the cooling capacity. This has no equivalent in the prior art.

[0011] The process water generated during operation of the respective fuel cell is used to adiabatically cool the air flow through the heat exchanger, which is used to cool the fuel cell, using the spray discharge device, including a reversal of the flow direction. This creates a cooling situation in which the air hitting the heat exchanger has a lower temperature than the ambient air. This temperature reduction means that greater cooling capacity can be achieved with the same heat exchangers as demonstrated in the prior art. This extends the temperature range in which the fuel cell can be operated, or conversely, the heat exchanger or the connected coolant circuit of the fuel cell system can be reduced in size, which in turn results in cost savings.

[0012] The solution according to the invention is of particular interest in the context of adiabatic building cooling. Furthermore, it is advantageous if a hood or housing design for vehicles or stationary machines is designed in such a way that any influences of unwanted ambient air currents on the sprayed water are minimized. The invention further relates to a cooling device as a subsystem for the fuel cell system presented above, as well as to the use of such a cooling device for such a fuel cell system.

[0013] In a preferred embodiment of the fuel cell system according to the invention, the spray nozzles of the discharge device are arranged between the fan and the heat exchanger such that the spray nozzles spray into the fan wake on the outlet side of the fan. The spray nozzles spray the water against the air flow generated by the fan into a space between this fan and the heat exchanger. The fan, which is usually designed as at least one axial fan, accordingly draws in ambient air on the inlet side, creating a suction, and expels the drawn-in air at an accelerated rate in the so-called wake on the outlet side toward the heat exchanger. In particular, the air flow flows through the heat exchanger. Furthermore, the heat exchanger can also be arranged between the spray discharge device and the fan.The fan then preferably sucks in the ambient air through the heat exchanger and the spray discharge device in turn sprays the water mist against the direction of the air flow, which leads to improved mist formation.

[0014] In a further alternative embodiment of the fuel cell system according to the invention, the spray nozzles of the discharge device are arranged upstream of the fan, as seen in the flow direction of the medium flow generated by the fan. The heat exchanger follows the fan in such a way that the spray nozzles spray into the fan suction on the inlet side of the fan. This results in a longer path for the water droplets emitted by the spray nozzles, which helps facilitate the adiabatic phase transition from "liquid" to "gaseous" to generate the atomized cooling medium. In a preferred embodiment of the fuel cell system according to the invention, a collecting container is connected in the line of the discharge device between the water separator and the feed pump.If the respective fuel cell generates too much water, this can be stored in the collection tank, which can supply the spray nozzles of the discharge device if there is too little water. The collection tank preferably has a dispensing device for hydrogen. During fuel cell operation, hydrogen can unintentionally enter the cooling fluid channels due to leaks, where it is dissolved in the cooling fluid in the form of water or is carried along in the cooling fluid as hydrogen bubbles. This accumulation of hydrogen in the cooling water can outgas in the collection tank and preferably be put to some kind of use. If no use is intended, the hydrogen gas that accumulates on the ambient side of the collection tank can also be burned off.Particularly preferably, it can be provided that the discharge device is part of a closed adiabatic cooling circuit which is connected to the collecting container on the inlet and outlet sides, which helps to avoid cooling losses.

[0015] The fan is a fluid-flow machine driven by a motor, for example, an electric motor, which conveys air as a gaseous medium from the fan's inlet side (fan suction) to its outlet side (fan wake), which is opposite the heat exchanger, preferably in the form of a plate heat exchanger. This allows the fan to then force the air drawn in from the environment through the gaps maintained between the fins of the heat exchanger. In particular, an axial fan is used, and the fan blades can create a laminar axial flow, at least on the outlet side of the fan, with a correspondingly high cooling input into the heat exchanger.The water released from the respective spray nozzle of the discharge device, which is in a nebulized form, can be centrally collected, particularly in stationary applications, and returned to a water cycle, for example, as part of a building's water supply. In mobile applications, the water can also be captured and collected; however, it is also possible to simply discharge the released water in pure form into the environment, such as the condensate produced by vehicle air conditioning systems.

[0016] In a further preferred embodiment of the fuel cell system according to the invention, the water separation device comprises a discharge device for cathode exhaust gas. The cathode discharge, which in particular comprises ambient air, can thus be separated from the liquid water by the fuel cell system, thus reducing the gas bubble entrainment in the spray water provided for the discharge device.

[0017] A cooling device as a subsystem for such a fuel cell system consists of at least a water separation device, a coolant pump, a heat exchanger, a coolant circuit connected to the heat exchanger, and a fan which generates a gaseous medium flow, in particular an air flow, through the heat exchanger, wherein a feed pump of a feed device conveys fluid from the water separation device to a discharge device which sprays the fluid into the environment by means of spray nozzles, and wherein the discharge device sprays the water by means of the spray nozzles in a direction opposite to the direction of the medium flow generated by the fan. In the following, the fuel cell system according to the invention and the associated cooling device are explained in more detail using exemplary embodiments according to the drawing. In the form of a fluidic circuit

[0018] Figure 1 shows a first embodiment of the cooling solution according to the invention;

[0019] Figure 2 shows a modified embodiment of the solution according to Figure 1 and

[0020] Figure 3 shows, in the form of an exploded view, the essential components of the cooling device used in Figures 1 and 2.

[0021] The fuel cell system shown as a whole in Figure 1 has a fuel cell stack 10 with a plurality of individual, correspondingly interconnected fuel cells 12. The fuel cell stack 10 has proton exchange membranes (not shown). Furthermore, the system has a coolant circuit 16 with a coolant pump 18 and a heat exchanger 20, for example in the form of a cross-flow heat exchanger with its individual cooling fins 23 as shown in Figure 3. Such coolant circuits 16 with their individual components are common for fuel cell systems, so they will not be discussed in more detail here. The cooling fluid used for the coolant circuit 16 is usually a mixture of ethylene glycol and water with varying concentrations in the composition and is supplied to and removed from the coolant via distributor pipes 25 and 27 laterally adjacent to individual flow channels.dissipated, wherein the flow channels are connected in the usual way to the distributor pipes 25, 27 for conducting a fluid to be tempered, in particular to be cooled. The individual flow channels are kept at a distance from one another plate by plate by means of fins 23, which form an air-side ribbing within the framework of the plate structure and in this respect serve as a surface extension for the heat exchanger, which guides the air flow of a fan 22. The glycol ensures in any case that the water cannot freeze even at low temperatures. To improve the cooling performance of the heat exchanger 20, the fan 22, preferably in the form of three identically constructed axial fans 29, is arranged in front of the heat exchanger 20.

[0022] The fuel cell stack 10, shown as a whole and simplified in block diagram, typically has an anode side and a cathode side. The anode side receives a hydrogen inlet gas via supply line 28. Furthermore, the cathode side receives an air flow via supply line 30. An aqueous cathode discharge occurs at the outlet side of the fuel cell stack 10 via a discharge line 32, which is connected to a water separation device 34 of conventional design, which separates water from the cathode discharge and discharges liquid water to a discharge line 36. The water separation device 34 can consist of a conventional water separator, which serves to mechanically separate water droplets from a gas flow. However, a physical separation of water from the gas flow by condensation is preferably induced. The cathode exhaust gas is discharged from the water separation device 34 via a line 38.At a corresponding fluid pressure in the discharge line 36, fluid flows into a collecting container 42. On the discharge side of the collecting container 42, a conveying device 46 is connected to a corresponding discharge line 44, for example in the form of a pressure pump 48, which, for example, has a discharge pressure of 5 to 15 bar for the fluid, such as water. In this respect, the discharge line 44 establishes a fluid-carrying connection between the pressure pump 48 and a discharge device, designated as a whole by 50, which, in the exemplary embodiment shown, has three individual spray nozzles 52 arranged one above the other. Several such spray nozzles 52 can also be arranged in groups in rows and columns, wherein the arrangement is preferably selected such that the free end face of the heat exchanger 20 is essentially reached by a spray application from the discharge device 50. A corresponding exemplary embodiment is explained in more detail in Fig. 3.The individual spray cones 54 generated by the nozzles 52 are indicated by dotted lines in the figure. The flow directions of the fluids in the corresponding lines are again indicated by arrows.

[0023] During operation of the fuel cell stack 10, heat is generated, which is transferred to the heat exchanger 20 via the closed coolant circuit 16. For this purpose, the coolant pump 18 transports the heated cooling fluid from the fuel cell stack 10, and after cooling via the heat exchanger 20, the cooled cooling fluid is transferred to the fuel cell stack 10 for further coolant circulation.

[0024] In addition, the process water inevitably generated during fuel cell operation is passed on via the water separation device 34 and the collection container 42 using the pump 48 via the discharge line 44 to the discharge device 50. Subsequently, under the action of the pump 48, the water is sprayed via the spray nozzles 52 in the direction of the fan 22. The water spray discharge, usually in the form of a water mist, mixes with the ambient air drawn in by the fan 22, which leads to a cooling of the air on the discharge side of the fan 22, i.e., before passing through the cooling fins of the heat exchanger 20. The air thus adiabatically cooled by the water mist increases the cooling capacity of the heat exchanger 20 and thus leads overall to an improvement in the cooling capacity in the coolant circuit 16.In addition to the adiabatic cooling due to the spray water discharge in the form of mist into the exhaust, convective cooling processes are also implemented through the use of the fan 22. The cooling device according to the invention, which can also be retrofitted to existing fuel cell systems within the outlined framework, is particularly suitable for use with low-temperature fuel cells, since the temperature difference between the ambient air and the fuel cell temperature to be maintained is small. With the cooling device according to the invention, effective cooling is achieved in a technically simple manner, without the need for the use of correspondingly large-volume cooling devices.Correspondingly good cooling performance can be achieved if a closed adiabatic circuit 56 is implemented with a supply line 58 from the collection container 42 via the conveying device 46 or the pressure pump 48 to the application device 50 and from there via a return line 60 back to the collection container 42. Except for the discharge via the individual nozzles 52, the aforementioned circuit 56 is closed in this respect. A shut-off valve 62 can be used to interrupt the relevant circuit 56, which is connected to the return line 60 downstream of the spray nozzles 52, viewed in the direction of fluid flow. Instead of the circuit 56 shown, only one supply line 58 to the spray nozzles 52 can be provided, and excess fluid not sprayed by the spray nozzles 52 enters the environment or enters a collecting tray (not shown in detail) on the underside of the discharge device 50.

[0025] The fan 22 has an intake direction 64 for ambient air, which is transported in the axial direction by means of the fan blades of the fan 22 toward the spray nozzles 52 of the discharge device 50. The three individual spray nozzles 52 then spray water, forming individual spray cones 54, in a direction opposite to the axial fan direction or intake direction 64 of the fan 22. The air flow cooled in this way then passes from the fan 22 into the spaces between the fins 23 of the heat exchanger 20. Preferably, the fan 22, with its axial fans 29, the heat exchanger 20, and the spray nozzle discharge device 50, is combined in a structural unit 66 in a common housing 68.In an embodiment not shown in detail, it is also possible to alternatively place the fan 22 on the other, opposite side of the heat exchanger 20, so that the heat exchanger 20 is located between the fan 22 and the spray discharge device 50. In this respect, the fan 22 then draws in the ambient air through the heat exchanger 20, again resulting in a flow pattern with the intake direction 64. In this respect, the spray discharge with the water mist also remains in place opposite to the intake direction 64.

[0026] The further modified embodiment according to Figure 2 relates to a lower right-hand drawing section according to Figure 1, again with heat exchanger 20, fan 22, and discharge device 50. Otherwise, the solution according to Figure 1 regarding the fuel cell stack 10 is retained; as are the connecting lines shown for the heat exchanger 20 and for the discharge device 50.

[0027] This is modified from the solution according to Figure 1 in that the individual spray nozzles 52, here in the form of two spray nozzles 52, now protrude beyond the fan 22 in the direction of its intake direction 64, with the spray cone discharge 54 again occurring opposite to the intake direction 64; however, the water droplets are then deflected by approximately 180° and, entrained by the intake flow of the fan 22, pass through the fan 22 parallel to the intake direction 64 and, thus nebulized, then impinge on the heat exchanger 20 with its individual fins 23. In this way, compared to the solution according to Figure 1, the path for the water droplets after discharge is extended, which helps facilitate the adiabatic conversion processes from "liquid" to "gaseous". In this respect, even better cooling performance can be achieved with the design according to Figure 2 than with the solution according to Figure 1.Furthermore, Figure 2 shows an open circuit without a return line 60. In this respect, too, the fan 22 can be placed on the other side of the heat exchanger 20, which is facing away from the spray nozzles 52.

[0028] The cooling device used in Figures 1 and 2 for the fuel cell stack 10 is explained in more detail below using one possible embodiment. Figure 3 shows a plate heat exchanger, a so-called cross-flow heat exchanger, as the heat exchanger 20 in the form of an exploded view. Between two distributor pipes 25 and 27, one as the inlet and one as the outlet for a cooling liquid, such as a water-glycol mixture, individual, parallel flow channels extend to one another. These channels carry the fluid to be cooled, such as hydraulic medium from a working hydraulic system. Between the flow channels are fins 23, which usually maintain equally spaced, free spaces for the air flow. The corresponding structure of a heat exchanger 20 is conventional, so it will not be discussed in more detail here.

[0029] On the opposite side, and thus facing the viewer of Figure 3, is shown the fan 22 with its three axial fans 29, which can be accommodated in a housing 68. Facing the housing 68, each axial fan 29 has grid-shaped openings to allow air to be drawn in from the surroundings. This wire construction, which is not shown in detail and is otherwise a common measure in axial fan construction, protects the fan blades (not shown in detail) of each axial fan 29 from damage and also protects operators from injury during operation.Furthermore, the respective axial fan 29 has, in the usual way, an electric motor 70 in the center for driving its fan blades, which also receives its supply current in the usual way via electrical connecting cables 72, each of which has a type of lamp terminal at its free end for connecting the fan 22 to an electrical supply network (not shown in detail). The individual axial fans 29 are fixed in the housing 68 and, during operation, air flows through the respective axial fan 29 in the direction of view in Figure 3 in the intake direction 64 from left to right via the circular fan openings 73 in the housing 68. The axially directed air is then blown through the spaces between the individual fins 23 of the heat exchanger 20, with the cooling air exiting again on the right side into the environment 20 after flowing through the heat exchanger 20.In this way, the fluid to be cooled, which is guided in the fins 23, is cooled by the air flow, whereby hot cooling fluid is supplied via the first distribution pipe 25 and then discharged, correspondingly cooled, via the second distribution pipe 27 from the heat exchanger 20 for its further use.

[0030] As Figure 3 further shows, the discharge device 50 for discharging water is arranged between the heat exchanger 20 and the fan 22. In this area, the discharge device 50 has two parallel pipes 74 as part of a pipe string 75, which, as shown in Figure 1, are connected at one end to the supply line 58 and at the other to the return line 60. In Figure 3, the relevant lines 58, 60 are only indicated as sections. Furthermore, for positioning, the straight pipes 74 are screwed into corresponding recesses 76 in the housing 68.

[0031] Each pipe 74 has nozzle-like openings 78, a total of four for each pipe 74, arranged in groups at different distances between them. A so-called hollow cone nozzle is inserted into each circular-cylindrical opening 78 (not shown in detail). This precision nozzle enables the atomization of liquid droplets, which, in the atomized state, are introduced into the airflow of the fan 22 against the fan blowing direction, leading to further cooling of the cooling airflow and thus to improved cooling results at the heat exchanger 20. This has no equivalent in the prior art.

Claims

Patent claims 1. A fuel cell system comprising at least one fuel cell (12), a coolant circuit (16) with a coolant pump (18) and a heat exchanger (20), a water separation device (34), and a fan (22) which generates a gaseous medium flow, in particular an air flow, through the heat exchanger (20), wherein, by means of a cooling device having a conveying device (46), the water separated in the water separation device (34) reaches a discharge device (50) which sprays the water into the environment by means of spray nozzles (52), characterized in that the discharge device (50) sprays the water by means of the spray nozzles (52) in a direction opposite to the direction of the medium flow generated by the fan (22).

2. Fuel cell system according to claim 1, characterized in that the spray nozzles (52) of the discharge device (50) are arranged between the fan (22) and the heat exchanger (20) in such a way that the spray nozzles (52) spray into the fan wake on the outlet side of the fan (22).

3. Fuel cell system according to claim 1 or 2, characterized in that the spray nozzles (52) of the discharge device (50) are arranged in front of the fan (22) in the flow direction of the medium flow generated by the fan (22), which is followed by the heat exchanger (20) in such a way that the spray nozzles (52) spray into the fan suction on the inlet side of the fan (22).

4. Fuel cell system according to one of the preceding claims, characterized in that a collecting container (42) is connected between the water separator (34) and the conveying device (46) in the line guide (44) of the discharge direction (50).

5. Fuel cell system according to one of the preceding claims, characterized in that the discharge device (50) is part of a closed adiabatic cooling circuit which is connected on the inlet and outlet sides to the collecting container (42).

6. Fuel cell system according to one of the preceding claims, characterized in that the collecting container (42) has a dispensing device for hydrogen.

7. Fuel cell system according to one of the preceding claims, characterized in that several fuel cells (12) are combined to form a stack (10), each with an inlet (28) for hydrogen and an inlet (30) for oxygen, which preferably originates from the ambient air.

8. Cooling device for a fuel cell system according to one of the preceding claims, consisting of at least one water separation device (34), a coolant pump (18), a heat exchanger (20), a coolant circuit (16) connected to the heat exchanger, and a fan (22) which generates a gaseous medium flow, in particular an air flow, through the heat exchanger (20), wherein a feed pump (48) of a feed device (46) feeds fluid from the water separation device (34) to a discharge device (50) which sprays the fluid into the environment by means of spray nozzles (52), characterized in that the discharge device (50) sprays the water by means of the spray nozzles (52) in a direction opposite to the direction of the medium flow generated by the fan (22).

9. Cooling device according to claim 8, characterized in that the heat exchanger (20) is formed from a cross-flow heat exchanger, that the fan (22) consists of several axial fans (29), and that the discharge device (50) has at least one fluid-carrying pipe rod (73) into which individual hollow cone nozzles are inserted as spray nozzles (52) for the adiabatical production of atomized cooling gas from liquid water.

10. Use of a cooling device according to claim 8 or 9 for a fuel cell system according to one of claims 1 to 7, characterized in that the water obtained during operation of the respective fuel cell (12) is passed on by means of a conveying device (46) to a discharge device (50) which, by means of spray nozzles (52), sprays water into the air transported by the fan (22) of the heat exchanger (20) against the air flow direction in order to generate an adiabatic cooling for the purpose of cooling the coolant in the coolant circuit (16) of the respective fuel cell

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