Method for operating a fuel cell system

Abstract

Fuel cell system (100) comprising at least one fuel cell stack (11), a cathode system (300) having a cathode outlet line (32), and a cooling circuit (400) having a cooling circuit line (45) in which a vehicle radiator (42) is arranged, wherein the cathode outlet line (32) and the cooling circuit (400) are thermally connected to one another.

Description

[0001] R. 416939

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for operating a fuel cell system;

[0006] The invention relates to a fuel cell system with the features of independent claim 1. Furthermore, the invention relates to a method for operating a fuel cell system.

[0007] State of the art

[0008] It is known from the prior art that fuel cell systems include a fuel cell stack, an anode system, a cathode system and a cooling circuit.

[0009] During operation of the fuel cell system, the reactants fuel and air flow into the fuel cell stack to obtain electrical energy in an electrochemical reaction.

[0010] The waste heat from the fuel cell stack is dissipated via a cooling circuit and can be released into the environment through a vehicle radiator. A coolant circulates within this cooling circuit.

[0011] Disclosure of the invention

[0012] The invention relates to a fuel cell system according to independent claim 1 and a method for operating a fuel cell system according to independent claim 9. Further features and details of the invention will become apparent from the respective dependent claims, the description and the drawings.

[0013] The fuel cell system and the method according to the invention have the advantage that the cooling capacity of the cooling circuit can be increased. This generally makes it possible to lower the temperature of the coolant in addition to the effect of R. 416939.

[0014] - 2 -

[0015] Lowering the vehicle's radiator. This also makes it possible to reduce the parasitic power consumption of auxiliary components such as the radiator fan, thereby increasing system efficiency and reducing fuel consumption.

[0016] When the maximum permissible temperature of the fuel cell stack is reached, particularly under high load demands and / or high ambient temperatures, the power output of the fuel cell stack is reduced ("derating"). The fuel cell system and method according to the invention make it possible to minimize derating. Additionally, it is possible to reduce the installation space required for a vehicle radiator, since additional cooling capacity is provided by the cooling circuit via the cathode exhaust using the cold cathode exhaust gas.

[0017] It is advantageous if the cathode exhaust and the cooling circuit are thermally connected via a heat exchanger. This makes additional cooling capacity of the cathode exhaust available for the cooling circuit of the fuel cell stack with the help of the heat exchanger.

[0018] Advantageously, the heat exchanger is located in the cathode outlet and in the cooling circuit line. This allows the cooling circuit to be thermally connected to the cathode outlet without the need for additional lines, thus enabling a space-optimized design and efficient operation of the fuel cell system.

[0019] It is advantageous if the heat exchanger is located upstream of the vehicle radiator in the cooling circuit line. This allows for the greatest possible temperature gradient between the cathode exhaust gas and the coolant temperature after exiting the fuel cell stack's coolant path, thus optimizing the heat exchanger's cooling capacity.

[0020] Advantageously, the heat exchanger is located in the cooling circuit downstream of the vehicle radiator. This allows a high coolant temperature to be maintained at the radiator inlet, thus optimizing the radiator's cooling capacity. If the radiator can no longer cool the coolant sufficiently, causing the coolant temperature to exceed a certain limit at the inlet, the heat exchanger provides additional cooling. R. 416939

[0021] - 3 -

[0022] It is advantageous to have a turbine in the cathode outlet and the heat exchanger positioned downstream of the turbine in the cathode outlet. The cathode exhaust gas is cooled as it expands through the turbine. This increases the temperature gradient between the coolant in the cooling circuit and the cathode exhaust gas, further improving cooling performance. Another thermodynamic effect is that liquid water in the exhaust gas fluid can evaporate or vaporize in the heat exchanger upon heat input and is then discharged in gaseous form. This enthalpy of vaporization provides an additional cooling effect.

[0023] Advantageously, an exhaust gas line containing a valve terminates at the cathode outlet. The cathode outlet and the cooling circuit are thermally connected by partially closing the valve. The exhaust gas line containing the valve allows for control of the mass flow rate of cathode exhaust gas through the heat exchanger. This enables targeted cooling of the cathode exhaust gas.

[0024] It is advantageous to thermally connect the cathode discharge and the cooling circuit via a heat exchanger when the coolant temperature exceeds a certain limit. This ensures that the cooling circuit is thermally connected to the heat exchanger when additional peak cooling is required.

[0025] Advantageously, the coolant temperature is measured via a temperature sensor located in the cooling circuit line. Using a temperature sensor allows for an accurate and reliable determination of the coolant temperature.

[0026] Description of the drawings

[0027] The fuel cell system and the method according to the invention are explained in more detail below with reference to drawings with preferred embodiments.

[0028] It shows: R. 416939

[0029] - 4 -

[0030] Fig. 1 shows a first embodiment of the fuel cell system according to the invention,

[0031] Fig. 2 shows a second embodiment of the fuel cell system according to the invention,

[0032] Fig. 3 shows a third embodiment of the fuel cell system according to the invention,

[0033] Fig. 4 shows a flowchart of the method according to the invention;

[0034] Figure 1 shows a first embodiment of the fuel cell system 100 with at least one fuel cell stack 11, an anode system 200, a cathode system 300 and a cooling circuit 400.

[0035] Cooling circuit 400 represents a closed fluid circuit. Cooling circuit 400 serves to temperature-control the at least one fuel cell stack 11 by flowing a coolant through a coolant path KM of the at least one fuel cell stack 11.

[0036] Cooling circuit 400 has a cooling circuit line 45, which forms a closed circuit in which a coolant circulates. A valve 41, a vehicle radiator 42, a pump unit 43, a temperature sensor 44, and a heat exchanger 47 are arranged in the cooling circuit line 45.

[0037] The vehicle cooler 42 is arranged downstream of the valve 41 in the direction of flow. The waste heat from the at least one fuel cell stack 11 can be dissipated to the environment via the vehicle cooler 42.

[0038] The pumping unit 43 is arranged between the vehicle radiator 42 and the at least one fuel cell stack 11. The pumping unit 43 supports the circulation of the coolant in the cooling circuit 400. A blower, in particular a radiator fan, can be arranged on the vehicle radiator 42.

[0039] A bypass line 46 runs parallel to the vehicle radiator 42. The bypass line 46 is connected to the valve 41 and opens downstream of the vehicle radiator 42 in the direction of flow. R. 416939

[0040] - 5 -

[0041] With the aid of valve 41, the coolant can be diverted, at least partially or completely, around the vehicle radiator 42 by directing the coolant into the bypass line 46. The coolant is diverted, at least partially or completely, around the vehicle radiator 42 by setting valve 41 to a switching position that allows the coolant to flow, at least partially or completely, through the bypass line 46.

[0042] In a first alternative embodiment, the valve 41 can also be arranged in the bypass line 46.

[0043] In a second alternative embodiment, the valve 41 can also be arranged at the junction of the bypass line 46 and the line downstream of the vehicle radiator 42, and upstream conveying device 43.

[0044] The temperature sensor 44 is arranged between the coolant path KM and the pump unit 43. The temperature sensor 44 can be used to determine the coolant temperature at the inlet of the at least one fuel cell stack 11.

[0045] The heat exchanger 47 is arranged in the cooling circuit line 45 upstream of the vehicle radiator 42 in the direction of flow. The coolant can be additionally cooled with the aid of the heat exchanger 47.

[0046] The cathode system 300 supplies a cathode chamber K with oxygen (O2) as a reactant. Oxygen is a component of air. By supplying air to the fuel cell system 100, the oxygen is made available to it as a reactant.

[0047] In the cathode system 300 a cathode inlet 31 and a cathode outlet 32 ​​are arranged.

[0048] The cathode supply line 31 opens into the at least one fuel cell stack 11 and supplies air to the at least one fuel cell stack 11. A conveying unit 33 is arranged in the cathode supply line 31.

[0049] The cathode outlet 32 ​​is connected to at least one fuel cell stack 11. Air and / or fluids, such as product water, are discharged from the cathode system 300 via the cathode outlet 32. R. 416939

[0050] - 6 -

[0051] A turbine 35 is arranged in the cathode outlet 32, and the turbine is used to cool the cathode exhaust gas. In the first embodiment, the turbine 35 is mounted on a common shaft 38 with the conveying unit 33. In an alternative embodiment, more than one conveying unit 33 can be arranged in the cathode inlet 31. This allows for a greater pressure difference between the cathode exhaust gas upstream of the turbine 35 and the cathode exhaust gas downstream of the turbine 35, thus further increasing the cooling of the cathode exhaust gas.

[0052] The cathode outlet 32 ​​and the cooling circuit 400 are thermally connected via the heat exchanger 47, in particular a gas-coolant heat exchanger.

[0053] In the first embodiment, the cathode outlet 32 ​​is thermally connected to the cooling circuit 400 via a heat exchanger 47, wherein the heat exchanger 42 is arranged in the cathode outlet 32 ​​downstream of the turbine 35 in the direction of flow.

[0054] The heat exchanger 47 is arranged in the cathode outlet 32 ​​and in the cooling circuit line 45, so that the cathode exhaust gas can additionally cool the coolant.

[0055] The anode system 200 supplies an anode compartment A of the at least one fuel cell stack 11 with a fuel or anode gas, in particular hydrogen (H2), as reactant.

[0056] The anode system 200 includes an anode supply line 22, a recirculation line 21, an anode outlet 23 and a jet pump 26.

[0057] The anode supply line 22 is connected to a fuel tank (not shown) and leads into the anode compartment K of the at least one fuel cell stack 11. Fuel is supplied from the fuel tank (not shown) to the anode compartment A via the anode supply line 22 and made available as reactant.

[0058] The recirculation line 21 is connected to the anode chamber A and leads into the jet pump 26. The supply of fuel to the at least one R. 416939

[0059] - 7 -

[0060] Fuel cell stack 11 can operate superstoichiometrically, so that fuel is still contained in the anode exhaust. To make the fuel available to the anode system, anode exhaust is recirculated from the recirculation line 21 into the anode supply line 22.

[0061] A jet pump 26 is arranged in the anode supply line 22. The jet pump is arranged between the anode supply line 22 and the recirculation line 21 and connects them.

[0062] An anode outlet 23 is arranged in the anode system 200. The anode outlet 23 is connected to the recirculation line 21. Gases, such as anode exhaust gas and / or fluids, such as product water, are discharged from the anode system 200 via the anode outlet 23.

[0063] A control unit 500 is provided to regulate and control processes in the fuel cell system 100. This also includes the processing of at least one measurement signal for the execution of the method according to the invention.

[0064] Figure 2 shows a second embodiment of the fuel cell system 100. The second embodiment of the fuel cell system 100 corresponds to the first embodiment of the fuel cell system 100 except for the differences mentioned below.

[0065] In the second embodiment, the turbine 35 is not mounted on a common shaft 38 with the conveying unit 33.

[0066] The heat exchanger 47 is located in the cooling circuit line 45 downstream of the vehicle radiator 42 in the direction of flow.

[0067] In a first alternative embodiment of the second embodiment, the anode outlet 23 opens into the cathode outlet 32 ​​downstream of the heat exchanger 47, so that in the alternative embodiment of the second embodiment both cathode exhaust gas and anode exhaust gas are discharged from the fuel cell system 100 via the cathode outlet 32.

[0068] In a second alternative embodiment of the second embodiment, the anode lead 23 opens into the cathode lead 32 upstream. R. 416939

[0069] - 8 - of the heat exchanger 47. In this case, liquid water present in the discharged anode gas can make an additional contribution to the cooling effect through evaporation and / or vaporization.

[0070] Figure 3 shows a third embodiment of the fuel cell system 100. The third embodiment of the fuel cell system 100 corresponds to the second embodiment of the fuel cell system 100 except for the differences mentioned below.

[0071] An exhaust line 36 opens at the cathode outlet 32. A valve 34 is arranged in the exhaust line 36. In an alternative embodiment, the anode outlet 23 opens into the exhaust line 36 downstream of the valve 34, so that in the alternative embodiment both cathode exhaust and anode exhaust are discharged from the fuel cell system 100 via the exhaust line 36.

[0072] The mass flow rate of cathode exhaust gas flowing through the heat exchanger 47 can be adjusted using the valve 34. When the valve 34 is in an open switching position, essentially no mass flow of cathode exhaust gas flows through the heat exchanger 47. When the valve 34 is in a partially closed switching position, a correspondingly partial amount of cathode exhaust gas can flow through the heat exchanger 47.

[0073] In an alternative embodiment of the third exemplary embodiment, a further valve is arranged in the cathode outlet 32 ​​downstream of the exhaust gas line 36. The valve 34 and the further valve can also be combined in a 3-way valve.

[0074] The features of the first embodiment, the second embodiment and the third embodiment can be combined and / or exchanged to obtain further advantageous embodiments of the fuel cell system 100 according to the invention.

[0075] Figure 4 shows an embodiment of the method according to the invention.

[0076] Using the method according to the invention, the cooling capacity of the cooling circuit 400 for cooling the fuel cell stack 11 can be increased. This is achieved by R. 416939

[0077] - 9 - via the heat exchanger 47 the cold cathode exhaust gas additionally cools the coolant. In particular, the method according to the invention can be carried out as long as an ambient temperature of the fuel cell system 100 and / or a temperature of the coolant is above a temperature threshold.

[0078] The process is initiated in step S100. The process according to the invention is carried out during the operation of the fuel cell system 100.

[0079] In step S200, the coolant temperature is determined and then compared with a first temperature limit. The coolant temperature can be measured using a model and / or via a temperature sensor 44 located in the cooling circuit line 45. In a first embodiment, the coolant temperature is determined before it enters the coolant path KM. In a second embodiment, the coolant temperature is determined after it exits the coolant path KM.

[0080] If the coolant temperature exceeds a first temperature limit, step S300 is then executed. The first temperature limit can be, for example, 90°C.

[0081] In step S300, the cathode outlet 32 ​​and the cooling circuit 400 are thermally connected via the heat exchanger 47 by at least partially opening the valve 34, which is located in the exhaust line 36, into a closed switching position. This allows cathode exhaust gas to flow into the heat exchanger 47.

[0082] Subsequently, in step S400, a defined period of time elapses so that the cathode exhaust gas can cool the coolant via the heat exchanger 47.

[0083] After the defined time period has elapsed, step S200 is executed again.

[0084] If the coolant temperature falls below the first temperature limit in step S200, step S500 is then executed. The inventive process is terminated in step S500. R. 416939

[0085] - 10 -

[0086] In an alternative embodiment of the method according to the invention, step S400 is executed until the temperature of the coolant falls below a second temperature limit. Step S500 is then executed.

[0087] In an alternative embodiment, the method according to the invention can be carried out continuously in order to check at regular intervals during the operation of the fuel cell system whether additional cooling of the coolant via the cathode exhaust gas is advantageous.

[0088] The process can still be carried out, at least in part, by the control unit 500 of the fuel cell system 100. A computer program in the form of code can be stored in a memory unit of the control unit 500. When executed by a processing unit of the control unit 500, this code performs a process that can proceed as described above. The same advantages described above in connection with the process according to the invention can be achieved using the control unit 500. These advantages are fully referenced herein.

[0089] The control unit 500 can control the actuators in the fuel cell system 100 in order to carry out the procedure accordingly.

[0090] Furthermore, the control unit 500 can be in a communication link with an external computing unit in order to outsource some process steps and / or calculations completely or partially to the external computing unit.

[0091] According to another aspect, the invention provides a computer program product comprising instructions which, when executed by a computer, such as the processing unit of the control unit 500, cause the computer to carry out the method, which can proceed as described above. The computer program product offers the same advantages described above in connection with the method and / or the control unit 500 according to the invention. These advantages are fully referenced herein.

Claims

R. 416939 - 11 - Claims 1. Fuel cell system (100), comprising at least one fuel cell stack (11), a cathode system (300) with a cathode outlet (32) and a cooling circuit (400) with a cooling circuit line (45) in which a vehicle radiator (42) is arranged, characterized in that the cathode outlet (32) and the cooling circuit (400) are thermally connected to each other.

2. Fuel cell system (100) according to claim 1 , characterized in that the cathode discharge (32) and the cooling circuit (400) are thermally connected to each other via a heat exchanger (47).

3. Fuel cell system (100) according to claim 2, characterized in that the heat exchanger (47) is arranged in the cathode outlet (32) and in the cooling circuit line (45).

4. Fuel cell system (100) according to claim 2, characterized in that the heat exchanger (47) is arranged in the cooling circuit line (45) in the direction of flow upstream of the vehicle radiator (42).

5. Fuel cell system (100) according to claim 2, characterized in that the heat exchanger (47) is arranged in the cooling circuit line (45) in the flow direction behind the vehicle radiator (42).

6. Fuel cell system (100) according to claim 2, characterized in that a turbine (35) is arranged in the cathode outlet (32) and the heat exchanger (42) is arranged in the cathode outlet (32) in the flow direction behind the turbine (35).

7. Fuel cell system (100) according to claim 1 , characterized in that an exhaust gas line (36) opens at the cathode outlet (32) in which a valve (34) is arranged. R. 416939 - 12 - 8. A method for operating a fuel cell system (100) comprising at least one fuel cell stack (11), a cathode system (300) with a cathode outlet (32), and a cooling circuit (400) with a cooling circuit line (45) in which a vehicle radiator (42) is arranged, characterized in that the cathode outlet (32) and the cooling circuit (400) are thermally connected to each other via a heat exchanger (47) when the temperature of the coolant exceeds a temperature limit.

9. A method according to claim 8, characterized in that the cathode outlet (32) and the cooling circuit (400) are thermally connected to each other by at least partially opening a valve (34) arranged in an exhaust line (36) to a closed switching position.

10. A method according to claim 8, characterized in that the temperature of the The temperature of the coolant is measured via a temperature sensor (44) which is located in the cooling circuit line (45).

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