Fuel cell system; method for operating a fuel cell system

Abstract

A fuel cell system (100) comprising at least one fuel cell stack (11) in which an integrated coolant path (44) is arranged, a first cooling circuit (45) in which a vehicle cooler (42), a first delivery unit (43), the integrated coolant pad (44) and a bypass 3-way valve (41) are arranged, and a first bypass line (46) arranged parallel to the vehicle cooler (42), and an anode system (200) and a cathode system (300), wherein the fuel cell system (100) comprises: - a second bypass line (47) arranged in the first cooling circuit (45) parallel to the vehicle radiator (42) and between the vehicle radiator (42) and the first bypass line (46) and - a second delivery unit (49) arranged in the second bypass line (47) and - at least one means for decoupling a coolant cooling circuit from the first cooling circuit (45), wherein the second bypass line (47), the vehicle radiator (42) and the second delivery unit (49) are arranged in the coolant cooling circuit (45)

Description

The invention relates to a fuel cell system having the features of the preamble of independent claim 1.Prior ArtIt is known from the prior art that fuel cell systems exist which have an anode system and a cathode system. The anode system consists of an anode feed line which feeds fuel, in particular hydrogen, to a fuel cell stack, and a recirculation line which returns anode off-gas into the anode feed line by means of a conveying unit. Furthermore, the cathode system consists of a cathode feed line, in which a compressor can be arranged, and a cathode outlet line, by which cathode exhaust gas is conveyed from the cathode system into the exhaust line.The waste heat of the fuel cell stack is dissipated by means of a cooling circuit and can be discharged to the environment via a vehicle cooler. A coolant is recirculated in the cooling circuit. The coolant is pumped through the fuel cell stack by means of a coolant pump. A 3-way valve allows the vehicle radiator to be partially or fully bypassed.Disclosure of the InventionThe fuel cell system according to the invention has at least one fuel cell stack in which an integrated coolant path is arranged. Furthermore, the fuel cell system according to the invention has a first cooling circuit in which a vehicle radiator, a first delivery unit, the integrated coolant pad and a by-pass 3-way valve are arranged, and a first bypass line which is arranged parallel to the vehicle radiator. A coolant is located in the cooling circuit. The fuel cell system according to the invention has an anode system and a cathode system.The fuel cell system advantageously has a second bypass line which is arranged in the first cooling circuit parallel to the vehicle radiator and between the vehicle radiator and the first bypass line. By means of the second bypass line, it is possible to form a coolant cooling circuit. The second bypass line, the vehicle cooler and the second delivery unit are arranged in the coolant cooling circuit.It is advantageous if a second delivery unit is arranged in the second bypass line. The flow of the coolant is assisted by the delivery unit. Furthermore, the flow quantity and the flow direction can be influenced by the second conveying unit.Advantageously, the fuel cell system comprises at least one means for decoupling a coolant cooling circuit from the first cooling circuit. By decoupling, the coolant located in the coolant cooling circuit may be set to a different temperature than the coolant located in the first cooling circuit.It is advantageous if the at least one means for decoupling the coolant cooling circuit is arranged between the first bypass line and the second bypass line, so that the coolant cooling circuit is decoupled from the first cooling circuit in a targeted manner.Advantageously, the at least one means for decoupling the coolant cooling circuit is designed as a valve, in particular a shut-off valve and / or a 3-way valve. A valve, in particular a shut-off valve and / or 3-way valve, is a component which is regularly used in the technical field and is cost-effective and enables a compact construction of the fuel cell system.It is advantageous if the second delivery unit can be coupled in from an external cooling circuit which is arranged in the fuel cell system. This makes it possible to resort to an already present component in the fuel cell system and to allow a space-saving and cost-effective construction, since a delivery unit can be saved.It is advantageous if at least one further fuel cell stack with a second cooling circuit can be coupled into the second bypass line. This makes it possible to carry out the method according to the invention in a fuel cell system having a plurality of fuel cell stacks. It is thereby possible for a plurality of fuel cell stacks to share a second delivery unit and it is thereby possible to dispense with the use of further delivery units, as a result of which a compact and cost-effective construction is made possible.Advantageously, a second vehicle cooler, a second by-pass 3-way valve, a third delivery unit and a third bypass line are arranged in the second cooling circuit, wherein the third bypass line is arranged parallel to the second vehicle cooler. As a result, it is possible to carry out the method according to the invention also in the second cooling circuit.It is advantageous if the vehicle cooler cooling circuit can be decoupled from the first cooling circuit by actuating a means for decoupling the vehicle cooler cooling circuit from the first cooling circuit. Thereby, it is possible to set the coolant that is in the vehicle radiator cooling circuit to a different temperature than the coolant that is in the first cooling circuit.Advantageously, the vehicle cooler cooling circuit is decoupled from the first cooling circuit and as a result the temperature of the coolant in the first cooling circuit is held or increased by supplying waste heat of the at least one fuel cell stack to the temperature which previously existed in the fuel cell stack. This makes it possible to maintain the temperature of the coolant in the first cooling circuit at the temperature or to set it to a higher temperature without requiring an additional heating unit, whereby a cost-effective and space-saving design can be ensured.It is advantageous if the vehicle radiator cooling circuit is decoupled from the first cooling circuit and the temperature of coolant in the vehicle radiator cooling circuit is thereby reduced by the dissipation of heat via the vehicle radiator. As a result, a portion of the coolant can be cooled and can be made available to the first cooling circuit if required.It is advantageous if the decoupling of the vehicle cooler cooling circuit from the first cooling circuit takes place before and / or during a drying process of the at least one fuel cell stack. As a result, the method according to the invention can efficiently support the drying process.Advantageously, the vehicle radiator cooling circuit is decoupled from the first cooling circuit during a first drying step at high temperatures, in particular in the range from 50° C. to 80° C., and coupled in during a second drying step at low temperatures, in particular in the range from 1° C. to 30° C.As a result, in a two-stage drying method with a first drying step at high temperatures, in particular in the range from 50° C. to 80° C., and with a second drying step at low temperatures, in particular in the range from 1° C. to 30° C., the two-stage drying method can be carried out more efficiently.During the first drying step, the coolant can already be cooled in the vehicle radiator cooling circuit, so that the second drying step can take place in a shorter time since the coolant in the vehicle radiator cooling circuit has a low temperature or has been precooled. When the radiator cooling circuit is injected into the first cooling circuit, the low-temperature refrigerant is mixed with the refrigerant from the first high-temperature cooling circuit, and the target temperature of the second drying step can be achieved efficiently and quickly.The fuel cell system in the sense of the invention can preferably be used for mobile applications, for example in vehicles, in particular fuel-driven vehicles. The fuel cell system in the sense of the invention can serve as a main energy supplier for a vehicle. At the same time, however, it is also conceivable that the fuel cell system in the sense of the invention can be a power take-off and / or auxiliary drive of a vehicle, for example a hybrid vehicle. The fuel cell system in the sense of the invention can also be used for stationary applications, for example in generators.DESCRIPTION OF THE DRAWINGSThe fuel cell system according to the invention and the method according to the invention are explained in more detail below with reference to drawings with preferred exemplary embodiments.The following are shown: FIG. 1 shows a schematic topology of a fuel cell system according to a first exemplary embodiment, and FIG. 2 shows a schematic topology of a fuel cell system according to a second exemplary embodiment, and FIG. 3 shows a schematic topology of a fuel cell system according to a third exemplary embodiment, and FIG. 4 shows a flow chart of the method according to the invention.FIG. 1 shows a schematic topology of a fuel cell system 100 having at least one fuel cell stack 11 and a first cooling circuit 45, an anode system 200 and a cathode system 300.The anode system 200 supplies an anode space A of the fuel cell stack 11 with a fuel or anode fluid, in particular hydrogen (H 2) as reactants. The anode system includes an anode feed line 22 and a recirculation line 21, and anode off-gas is recirculated from an anode space A, which is arranged in the fuel cell stack 11, to the anode feed line 22 via the recirculation line 21. Between the anode feed line 22 and the recirculation line 21, a jet pump with metering valve 23 is arranged.The cathode system 300 supplies a cathode space K with oxygen (O 2) as a reactant. Oxygen forms a constituent of air. By supplying air into the fuel cell system 100, the oxygen is made available to the fuel cell system as a reactant.A cathode feed line 31 is arranged in the cathode system 300 and opens into the fuel cell stack 11. Oxygen is supplied to the fuel cell stack 11 via the cathode feed line 31.A cathode compressor 33 is located inside the cathode feed line 31; the cathode compressor 33 conveys air into the fuel cell stack 11; a cathode outlet line 32 is arranged in the cathode system 300. Gases, such as cathode exhaust gas and / or fluids, such as product water, are discharged from the cathode system 300 via the cathode outlet line 32.In the fuel cell system 100, the first cooling circuit 45 is disposed. The first cooling circuit 45 serves for the temperature control of the fuel cell stack 11 in that a coolant flows through an integrated coolant path 44 of the fuel cell stack 11.A first delivery unit 43, a first bypass 3-way valve 41, a first bypass line 46, the integrated coolant path 44 and a vehicle radiator 42 are arranged in the first cooling circuit 45. Furthermore, a second bypass line 47, a second delivery unit 49, a first valve 50 and optionally a check valve 48 are arranged in the first cooling circuit 45.The first bypass line 46 is arranged in parallel with the vehicle radiator 42. The second bypass line 47 is arranged in parallel with the vehicle radiator 42 and is arranged between the vehicle radiator 42 and the first bypass line 46.The integrated coolant path 44 is arranged in parallel with the first bypass line 46 within the fuel cell stack 11. By coolant flowing through the integrated coolant path 44, the fuel cell stack 11 can be temperature-controlled, in particular heated, cooled or kept at a temperature.The first delivery unit 43 is arranged upstream of the integrated coolant path 44 in the flow direction and supports the flow of the coolant.The second delivery unit 49 is arranged within the second bypass line 47 and the check valve 48; the first valve 50 is arranged between the first bypass line 46 and the second bypass line 47.It is possible to decouple a vehicle radiator cooling circuit from the first cooling circuit 45. In the vehicle radiator cooling circuit, the second bypass line 47, the second delivery unit 49 and the vehicle radiator 42 are arranged.The first valve 50 may be the at least one means for decoupling the vehicle radiator cooling circuit from the first cooling circuit 45. Thus, the at least one means for decoupling the vehicle radiator cooling circuit is arranged between the first bypass line 46 and the second bypass line 47. The first valve 50 is preferably designed as a shut-off valve.The second delivery unit 49 can be a pump, a compressor or a blower. The second delivery unit can be coupled in from an external cooling circuit and used for carrying out the method according to the invention.In the first cooling circuit 45, the coolant is recirculated by means of the first delivery unit 43. The first bypass 3-way valve 41 may direct the coolant partially or entirely past the vehicle radiator 42 via the first bypass line 46.The first bypass 3-way valve 41 may constitute the at least one means for decoupling the vehicle radiator cooling circuit from the first cooling circuit 45. For this purpose, the first bypass 3-way valve 41 is set to a switching position in which the first bypass 3-way valve 41 can be flowed through in the direction of the first bypass line 46. This allows the coolant to recirculate into the first bypass line 46 via the coolant path 44. The recirculation of the coolant is assisted by the first conveying unit 43.At least one sensor can optionally be arranged in the first cooling circuit 45. The sensor may be arranged upstream before the coolant path 44 and / or downstream after the coolant path 44, for example.A control unit 500 is provided in order to control or regulate all control and control processes in the fuel cell system 100.This also includes the processing of at least one measurement signal for carrying out the method according to the invention.FIG. 2 shows a schematic topology of the fuel cell system 100 according to a second exemplary embodiment. The second schematic topology of the fuel cell system 100 includes at least a fuel cell stack 11, an anode system 200 and a cathode system 300.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.In the first cooling circuit 45, the first valve 50 is disposed between and connects the second bypass line 47 and the first cooling circuit 45. In the second exemplary embodiment, the first valve 50 is designed as a 3-way valve.FIG. 3 shows a schematic topology of the fuel cell system 100 according to a third exemplary embodiment. The third schematic topology of the fuel cell system 100 includes at least a fuel cell stack 11, an anode system 200 and a cathode system 300.The third embodiment of the fuel cell system 100 corresponds to the first embodiment of the fuel cell system 100 except for the differences mentioned below.In the third exemplary embodiment, a further fuel cell stack 12 having a second cooling circuit 65 was coupled into the second bypass line 47. A second anode space A 6, a second cathode space K 6 and a further coolant path KM 6 are arranged in the fuel cell stack 12.A second vehicle radiator 62, a second bypass 3-way valve 61, a third delivery unit 63, a second valve 60 and a third bypass line 66 are arranged in the second cooling circuit 65, wherein the third bypass line 66 is arranged in parallel with the second vehicle radiator 62.Optionally, a third valve 51 is arranged in the second bypass line 47.FIG. 4 shows an exemplary embodiment of the method according to the invention.The fuel cell system 100 according to the invention and the method according to the invention make it possible to efficiently dry the fuel cell system 100 by precooling a portion of the coolant. For this purpose, in a first drying phase at high temperatures, the coolant is partially cooled down in the decoupled coolant circuit in order to be able to cool down the warmer fraction of the coolant more quickly with the precooled fraction of the coolant in a second drying phase, which takes place at low temperatures. As a result, the fuel cell system 100 can also be cooled down more quickly for the second drying step.In a step S 100, the method is started. The method is preferably started before a drying process or in parallel with a drying process.In a step S 200, the vehicle cooler cooling circuit is decoupled from the first cooling circuit 45 by actuating at least one means for decoupling the vehicle cooler cooling circuit. Decoupling the vehicle cooler cooling circuit from the first cooling circuit 45 preferably takes place before and / or during a drying process of the at least one fuel cell stack 11.As the at least one means for decoupling the vehicle radiator cooling circuit, the first valve 50 can be activated and, according to the first exemplary embodiment, set in a closed switching position, so that the first valve 50 can no longer be flown through.According to the second embodiment, the first valve 50 may be placed in a switching position in which the coolant flows from the vehicle radiator 42 direction into the second bypass line 47 via the valve 50.As the at least one means for decoupling the vehicle radiator cooling circuit, the first bypass 3-way valve 41 can be actuated, so that the first bypass 3-way valve 41 can only be flowed through from the direction of the coolant path 44 into the first bypass line 46.It is possible to actuate the first valve 50 and / or the first bypass 3-way valve for carrying out the method according to the invention. It is likewise possible for a different arrangement of components to be used and / or activated as the at least one means for decoupling the vehicle radiator cooling circuit.In a step S301, the coolant which is in the vehicle radiator cooling circuit is recirculated. To assist the recirculation of the coolant, the second conveying unit 49 can be activated.When the coolant flows through the radiator 42, the temperature of the coolant is reduced by releasing the heat of the coolant to the atmosphere via the radiator.In a step S 302, the coolant located in the first cooling circuit 45 is recirculated. To assist the recirculation of the coolant, the first conveying unit 43 can be activated.When the coolant flows through the integrated coolant path 44 located in the fuel cell stack 11, the temperature of the coolant is increased. The temperature of the coolant is increased by supplying waste heat from the fuel cell stack 11 to the coolant or transferring it into the coolant.In a step S 400, the first drying step for drying the anode space and / or the cathode space is carried out at high temperatures, in particular in the range from 50° C. to 80° C. Steps S 302 and S 301 may be performed in parallel with step S 400 and / or before step S 400.In step S 500, the vehicle radiator cooling circuit that was decoupled in step S 200 is coupled into the first cooling circuit 45. Thereby, the coolant located in the vehicle radiator cooling circuit can mix with the coolant located in the first cooling circuit 45. The coolant located in the first cooling circuit 45 can be cooled more quickly by mixing with coolant located in the vehicle radiator cooling circuit.The vehicle radiator cooling circuit is coupled by actuating the at least one means for decoupling the vehicle radiator cooling circuit and allowing the coolant to flow from the vehicle radiator cooling circuit into the coolant path 44 and allowing the coolant to flow from the coolant path 44 into the vehicle radiator cooling circuit.According to the first exemplary embodiment, the first valve 50 can be activated and placed in an open switching position, so that the first valve 50 can be flown through and the vehicle radiator cooling circuit is coupled back into the first cooling circuit 45.According to the second exemplary embodiment, the first valve 50 can be placed in a switching position in which the coolant flows from the direction of the vehicle radiator 42 via the valve 50 in the direction of the first delivery unit 43 and the vehicle radiator cooling circuit is coupled back into the first cooling circuit 45.The first bypass 3-way valve 41 can be controlled, so that the first bypass 3-way valve 41 can be flown through from the direction of the coolant path 44 via the first bypass 3-way valve 41 in the direction of the vehicle radiator 42 without flowing through the second bypass line 47 and the vehicle radiator cooling circuit is coupled back into the first cooling circuit 45.In a step S 600, the second drying step for drying the anode space and / or the cathode space is carried out at low temperatures, in particular in the range from 1° C. to 30° C.To set the low temperatures, the coolant is recirculated between the integrated coolant path 44 and the vehicle radiator 42.In step S 600, the method according to the invention is ended.The method according to the invention can be carried out in a fuel cell system 100 in a plurality of fuel cell stacks 11 in parallel or sequentially.The method may further be performed at least in part by the controller 500 of the fuel cell system 100. A computer program in the form of a code can be stored in a memory unit of the control unit 500, which computer program, when the code is executed by a computing unit of the control unit 500, carries out a method which can run as described above. With the aid of the control unit 500, the same advantages can be achieved as have been described above in connection with the method according to the invention. These advantages are referred to in the present case in their entirety.The control unit 500 may be in communication with the sensors of the fuel cell system 100 to monitor the sensor values.The control unit 500 can actuate the actuators in the fuel cell system 100 in order to carry out the method accordingly.In addition, the control unit 500 can be in a communication connection with an external computing unit in order to transfer some method steps and / or calculations wholly or partly to the external computing unit.

Claims

Fuel cell system (100) having at least one fuel cell stack (11) in which an integrated coolant path (44) is arranged, having a first cooling circuit (45) in which a vehicle cooler (42), a first feed unit (43), the integrated coolant pad (44) and a bypass 3-way valve (41) are arranged, and having a first bypass line (46) which is arranged parallel to the vehicle cooler (42), and having an anode system (200) and a cathode system (300), characterized in that the fuel cell system (100) has: - a second bypass line (47) which is arranged in the first cooling circuit (45) parallel to the vehicle cooler (42) and between the vehicle cooler (42) and the first bypass line (46), and - a second feed unit (49), which is arranged in the second bypass line (47), and - at least one means for decoupling a coolant cooling circuit from the first cooling circuit (45), wherein the second bypass line (47), the vehicle radiator (42) and the second delivery unit (49) are arranged in the coolant cooling circuit (45)Fuel cell system according to Claim 1, characterized in that the at least one means for decoupling the vehicle cooler cooling circuit is arranged between the first bypass line (46) and the second bypass line (47).Fuel cell system according to Claim 2, characterized in that the at least one means for decoupling the vehicle cooler cooling circuit is designed as a valve (50), in particular as a shut-off valve and / or a 3-way valve.Fuel cell system according to Claim 1, characterized in that the second delivery unit (49) can be coupled in from an external cooling circuit which is arranged in the fuel cell system.Fuel cell system according to Claim 1, characterized in that at least one further fuel cell stack (12) having a second cooling circuit (65) can be coupled into the second bypass line (47).Fuel cell system according to Claim 5, characterized in that a second vehicle cooler (62), a second bypass 3-way valve (61), a third delivery unit (63) and a third bypass line (66) are arranged in the second cooling circuit (65), the third bypass line (66) being arranged parallel to the second vehicle cooler (62).Method for operating a fuel cell system (100) according to one of the preceding claims, characterized in that the vehicle cooler cooling circuit can be decoupled from the first cooling circuit (45) by actuating a means for decoupling the vehicle cooler cooling circuit from the first cooling circuit (45).Method according to Claim 7, characterized in that the vehicle cooler cooling circuit is decoupled from the first cooling circuit (45), and the temperature of coolant in the first cooling circuit (45) is thereby held or increased by supplying waste heat from the at least one fuel cell stack (11).Method according to Claim 7, characterized in that the vehicle radiator cooling circuit is decoupled from the first cooling circuit (45), and the temperature of coolant in the vehicle radiator cooling circuit (45) is thereby reduced by the dissipation of heat via the vehicle radiator (42).Method according to Claim 7, characterized in that the decoupling of the vehicle cooler cooling circuit from the first cooling circuit (45) takes place before and / or during a drying process of the at least one fuel cell stack (11).Method according to Claim 7, characterized in that the vehicle radiator cooling circuit is decoupled from the first cooling circuit (45) during a first drying step at high temperatures, in particular in the range from 50°C to 80°C, and is coupled in during a second drying step at low temperatures, in particular in the range from 1°C to 30°C.

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