Method for operating a fuel cell system

Abstract

Method for operating a fuel cell system (100) with at least one fuel cell stack (11) consisting of a plurality of stacked fuel cells, wherein a membrane is arranged between the fuel cells, and an anode system (200) with a drain valve (24), and a cathode system (300), wherein during operation of the fuel cell system (100) a value is determined, wherein the value is a measure of a quantity of water in the anode system (200), and a reduction of the load point takes place if the value exceeds a limit value.

Description

[0001] The invention relates to a method for operating a fuel cell system having the features of the preamble of independent claim 1. State of the art

[0002] It is known from the prior art that fuel cell systems exist that have an anode system and a cathode system. The anode system consists of an anode supply line that supplies fuel to a fuel cell stack, and a recirculation line that recirculates anode exhaust gas to the anode supply line via a feed unit. A drain valve is located in the anode system through which liquid water can be drained from the anode system.

[0003] The cathode system consists of a cathode supply line, through which air is supplied to the fuel cell stack and in which a compressor can be located. A cathode outlet line is located in the cathode system, through which cathode exhaust gas is transported from the cathode system into the exhaust system. Disclosure of the invention

[0004] The method according to the invention for operating a fuel cell system with the features according to independent claim 1 can advantageously prevent accumulations of liquid water in the anode system which can no longer be removed from the fuel cell system via a drain valve.

[0005] An accumulation of liquid water in the anode system can lead to an undersupply of fuel, especially hydrogen, to the anode system.

[0006] In order to determine an accumulation of liquid water in the anode system that can no longer be removed from the fuel cell system via a drain valve, a value is determined during operation of the fuel cell system, whereby the value is a measure of the amount of water in the anode system, and the load point is reduced if the value exceeds a limit value.

[0007] During the chemical reaction in the fuel cell system, water (H2O) is formed. The higher the energy demand from the fuel cell system, the more water is formed by the chemical reaction in a defined period of time. To provide high amounts of energy, the fuel cell system is operated at a high load point.

[0008] If the value representing the amount of water in the anode system exceeds a limit, it is advantageous to reduce the load point, as it can no longer be guaranteed that the water quantity can be removed from the anode system. This can be particularly true under challenging environmental conditions, such as high relative humidity of 85% and high temperatures above 25 °C.

[0009] It is advantageous if the value represents the duration during which the drain valve is open, and the limit value represents the maximum permissible duration during which the drain valve is open. This provides an efficient way to determine whether there is an excessive amount of water in the anode system that can no longer be released through the drain valve.

[0010] It is advantageous if the limit value is determined as a function of the maximum flow rate of the drain valve, whereby the limit value represents a maximum permissible duration for which the drain valve is open. The limit value is increased the higher the maximum flow rate of the drain valve is, and the limit value is reduced the lower the maximum flow rate of the drain valve is. This allows the method according to the invention to be carried out more precisely and the limit value to be determined more accurately.

[0011] If the maximum flow rate of the drain valve increases as a function of the operating time of the drain valve, the maximum flow rate of the drain valve is advantageously determined as a function of the operating time. For this purpose, a table depicting the relationship between the maximum flow rate and the operating time of the drain valve can be used for the method according to the invention.

[0012] It is possible that an increased maximum flow rate could result in faster water removal from the anode system, resulting in not only water but also fuel being removed from the anode system, thereby reducing the efficiency of the fuel cell system. By determining the maximum flow rate of the drain valve as a function of operating time, the process can be optimized and the efficiency of the fuel cell system maintained.

[0013] It is advantageous if the value represents the amount of inflowing water from the water transfer from the cathode system to the anode system, with the water transfer taking place via the membrane. This allows the inflowing water to be quantified early on during the water transfer and systematically prevents a large amount of water from accumulating in the anode system, which could, for example, lead to an undersupply of hydrogen in the anode system.

[0014] Advantageously, the value is compared with the amount of water flowing out through the drain valve. The limit is exceeded if the value is greater than the amount of water flowing out. This allows for efficient determination of when the load point of the fuel cell system should be reduced. Optionally, the difference between the value and the amount of water flowing out can be used advantageously to specifically determine by what percentage the load point needs to be reduced.

[0015] The amount of incoming water from the water transfer from the cathode system to the anode system can advantageously be determined using a level sensor in the water separator. A level sensor is an established component that enables reliable and precise determination of the water quantity.

[0016] It is advantageous if the amount of inflowing water from the water transfer from the cathode system to the anode system is determined using a model, whereby the amount of inflowing water can be approximated, in particular, using the parameters of relative outside air humidity and outside temperature. The model can be a data-based model and / or a physical model. This eliminates the need for sensors, thus ensuring a compact and cost-effective design of the fuel cell system.

[0017] This is particularly the case when the operating parameters of the fuel cell system, such as a load point and / or a lambda value of the anode system and / or a lambda value of the cathode system and / or pressure conditions in the fuel cell system and / or temperatures in the fuel cell system and / or a flow rate of a coolant and / or a temperature of a coolant and / or an anode gas concentration, are known.

[0018] Advantageously, the reduction in the energy supplied by the fuel cell system resulting from the reduction in the load point is compensated for by supplying energy from an external energy storage device, in particular a battery. This keeps the amount of energy supplied constant, and the function of the devices being supplied is not affected. For example, when supplying energy to a vehicle's drive train, the method according to the invention can help the vehicle continue driving without reducing speed.

[0019] When implementing the method according to the invention in a vehicle, it is advantageous if the reduction in the load point of the fuel cell system is visualized in the vehicle. This allows the driver to be informed that, for example, a reduction in the energy provided is to be expected, and the driving behavior can be adjusted accordingly. Description of the drawings

[0020] The method according to the invention and the fuel cell system are explained in more detail below with reference to drawings with preferred embodiments.

[0021] They show: Fig. 1 a schematic topology of a fuel cell system and Fig. 2 a flowchart of the method according to the invention.

[0022] In Fig. 1 shows a schematic topology of a fuel cell system 100 with at least one fuel cell stack 11, an anode system 200, and a cathode system 300.

[0023] 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 the system as a reactant.

[0024] A cathode supply 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 supply line 31.

[0025] A cathode compressor 33 is located within the cathode supply 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.

[0026] The anode system 200 supplies an anode compartment A of the fuel cell stack 11 with a fuel or anode fluid, in particular hydrogen (H2), as a reactant. By supplying fuel to the anode compartment A, the fuel is made available to the fuel cell system 100 as a reactant.

[0027] The anode system includes an anode supply line 22, a recirculation line 21, an anode outlet line 23 and a water separator 30.

[0028] The anode supply line leads into the fuel cell stack 11. Fuel is supplied to the fuel cell stack 11 via the anode supply line 22.

[0029] The recirculation line 21 is connected to the anode chamber A and the anode supply line 22.

[0030] The fuel supply to the fuel cell stack 11 can be superstoichiometric, so that the anode exhaust gas still contains fuel. To make the fuel contained in the anode exhaust gas available to the anode system 200, the anode exhaust gas is recirculated from the recirculation line 21 into the anode supply line 22.

[0031] A recirculation conveying unit 25 is optionally arranged within the recirculation line 21. The recirculation conveying unit 25 supports the recirculation of the anode exhaust gas from the recirculation line 21 into the anode supply line 22.

[0032] A jet pump with a metering valve 26 is arranged in the anode supply line 22. The jet pump with a metering valve 26 is arranged between the anode supply line 22 and the recirculation line 21 and connects them.

[0033] The anode outlet line 23 is connected to the recirculation line 21. Gases, such as anode exhaust gas and / or fluids, such as water, are discharged from the anode system 200 via the anode outlet line 23.

[0034] A drain valve 24 is arranged in the anode outlet line 23. When the drain valve 24 is opened, water is drained from the anode system 200. The jet pump with metering valve 26 doses fuel into the anode system 200 accordingly to maintain a continuous flow rate.

[0035] In an alternative embodiment, the drain valve 24 may be designed as a combined purge-drain valve 24, so that anode exhaust gas and / or water can be discharged from the anode system 200 via the combined purge-drain valve 24.

[0036] The water separator 30 is arranged in the flow direction between the recirculation line 21 and the anode outlet line 23 and connects them to each other. The water separator 30 removes water from the anode exhaust gas. The water separator 30 can be designed in various embodiments: as an automatic water separator or as a manual water separator and / or with an additional filter and / or with additional active cooling. The water separator 30 can optionally include at least one fill level sensor.

[0037] A control unit 500 is provided to regulate and control all control-related processes in the fuel cell system 100. This also includes the processing of information for executing the method according to the invention.

[0038] The control unit 500 can communicate with the sensors in the fuel cell system 100 to monitor sensor values. The control unit 500 can control the actuators in the fuel cell system 100 to carry out the method according to the invention accordingly.

[0039] In addition, the control unit 500 can be in a communication connection with an external computing unit in order to outsource process steps and / or calculations in whole or in part to the external computing unit.

[0040] In Fig. 2 shows a flowchart of an exemplary method according to the invention.

[0041] The method according to the invention enables a targeted reduction in the amount of water produced during operation of the fuel cell system 100. The reduction in the amount of water produced is achieved by reducing the load point of the fuel cell system 100. When the load point is reduced, less water is formed because less reactant conversion takes place. As a result, the operation of the fuel cell system 100 can be maintained under changed environmental conditions, such as high relative outside air humidity of, for example, 85%, at which more water is introduced into the fuel cell system 100 than under normal conditions of, for example, 53% relative air humidity, because it is specifically prevented that a quantity of water accumulates in the anode system 200 that can no longer be removed from the anode system 200 and at which the fuel cell system 100 can no longer be operated.

[0042] The method is initiated in step S100. The method according to the invention is initiated or executed during operation of the fuel cell system 100.

[0043] In step S200, a value is determined, wherein the value is a measure of a quantity of water in the anode system 200.

[0044] In a first embodiment, the value may represent a duration during which the drain valve 24 is open. The value may be determined, for example, via the control unit.

[0045] In a second embodiment, the value may represent an amount of inflowing water from the water transfer from cathode system 300 to anode system 200, wherein the water transfer occurs via the membrane. The membrane is arranged between the stacked fuel cells in fuel cell stack 11.

[0046] The amount of inflowing water from the water transfer from cathode system 300 to anode system 200 can be determined via a level sensor arranged in the water separator 30.

[0047] In a third embodiment, the amount of inflowing water from the water transfer from cathode system 300 to anode system 200 can be determined using a model, wherein the amount of inflowing water can be approximated, in particular, using the parameters of relative outside air humidity and outside temperature. The higher the relative outside air humidity and the outside temperature, the more water can be expected to enter the anode system. The relative outside air humidity is a relative air humidity that exists outside the fuel cell system 100. The outside temperature is a temperature that exists outside the fuel cell system 100.

[0048] In step S300, the value is compared with a limit value and checked whether the value exceeds the limit value.

[0049] In the first embodiment, the value represents a duration in which the drain valve 24 is open and the limit value represents a maximum permissible duration in which the drain valve 24 is open.

[0050] The limit value can be determined depending on the maximum flow rate of the drain valve 24. The limit value is increased the higher the maximum flow rate of the drain valve 24 is, and the limit value is reduced the lower the maximum flow rate of the drain valve 24 is.

[0051] If the maximum flow rate of the drain valve 24 depends on the operating time of the drain valve 24, the limit value can be determined depending on the operating time of the drain valve 24. The maximum flow rate of the drain valve 24 can be determined using a table depending on the operating time of the drain valve 24.

[0052] In the second embodiment and the third embodiment, the limit value is exceeded when the value is greater than the amount of water flowing out through the drain valve 24. The value is an amount of water flowing in from the water transfer from the cathode system 300 to the anode system 200.

[0053] If the check in step S300 reveals that the value exceeds the limit, step S400 is executed. Subsequently, step S500 is executed.

[0054] In step S400, the load point of the fuel cell system 100 is reduced. The reduction in the energy provided by the fuel cell system 100 resulting from the reduction in the load point can be compensated for by providing energy from an external energy storage device, in particular a battery.

[0055] Optionally, in an additional step, if the fuel cell system 100 is arranged in a vehicle, the reduction of the load point of the fuel cell system 100 in the vehicle can be visualized.

[0056] If the check in step S300 reveals that the value does not exceed the limit value, step S500 is executed. In step S500, the method according to the invention is terminated.

[0057] In an alternative embodiment, it is also possible to carry out the method according to the invention with more than one fuel cell stack 11.

[0058] The method according to the invention can be carried out in parallel or sequentially in a fuel cell system 100 with several fuel cell stacks 11.

[0059] According to a further aspect, the invention provides a computer program product comprising instructions that, when the computer program product is executed by a computer, such as the processing unit of the control unit, cause the computer to perform the method, which can proceed as described above. Using the computer program product, the same advantages can be achieved as described with the control unit according to the invention.

Claims

[1] Method for operating a fuel cell system (100) with at least one fuel cell stack (11) consisting of a plurality of stacked fuel cells, wherein a membrane is arranged between the fuel cells, and an anode system (200) with a drain valve (24), and a cathode system (300), characterized by that during operation of the fuel cell system (100) a value is determined, wherein the value is a measure of a quantity of water in the anode system (200), and a reduction of the load point takes place if the value exceeds a limit value. [2] Method according to claim 1, characterized by that the value represents a duration in which the drain valve (24) is open. [3] Method according to claim 2, characterized by that the limit value is formed as a function of the maximum flow rate of the drain valve (24). [4] Method according to claim 3, characterized bythat the maximum flow rate of the drain valve (24) is determined as a function of the operating time of the drain valve (24). [5] Method according to claim 1, characterized by that the value represents an amount of inflowing water from the water transfer from cathode system (300) to anode system (200), wherein the water transfer takes place via the membrane. [6] Method according to claim 5, characterized by that the value is compared with a quantity of water flowing out via the drain valve (24) and the limit value is exceeded if the value is greater than the quantity of water flowing out. [7] Method according to claim 5, characterized by that the quantity of inflowing water from the water transfer from the cathode system (300) to the anode system (200) is determined via a level sensor in the water separator (30). [8] Method according to claim 5, characterized bythat the amount of inflowing water from the water transfer from the cathode system (300) to the anode system (200) is determined via a model, in particular via a combination of relative outside air humidity and outside temperature. [9] Method according to claim 1, characterized by that the reduction in the energy provided by the fuel cell system (100) resulting from the reduction in the load point is compensated by providing energy from an external energy storage device, in particular a battery. [10] Method according to claim 1, characterized by that the fuel cell system (100) is arranged in a vehicle and the reduction of the load point of the fuel cell system (100) is visualized in the vehicle.

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