Fuel cell system and operating method for a fuel cell system

Abstract

The invention relates to a fuel cell system (100) for converting energy, said fuel cell system (100) comprising:-a fuel cell stack (101),-an anode branch (103) for supplying fuel to the fuel cell stack (101),-a bleed valve (105) for bleeding anode gas from the anode branch (103),-a metering valve (107) for metering fuel into the anode branch (103),-a computing unit (109), the computing unit (109) is configured to actuate the metering valve (107) in a pulsed manner, and wherein the computing unit (109) is further configured to actuate the discharge valve (105) in a pulsed manner as a function of the actuation of the metering valve (107).

Description

Technical Field

[0001] The present invention relates to a fuel cell system according to the appended claims and a method for operating the fuel cell system. Background Technology

[0002] Hydrogen-based fuel cell systems are considered a future mobility concept because they produce only water as exhaust gas and enable rapid refueling.

[0003] When operating a fuel cell system, it is known that the anode gas is recirculated to maintain minimal hydrogen loss and maximize inlet humidity.

[0004] For recirculation, one can either use a so-called "jet pump," a recirculation blower, or a combination of the two concepts.

[0005] During fuel cell system operation, water and nitrogen accumulate in the anode circuit, gradually displacing hydrogen. To avoid extremely low hydrogen concentrations and reduce energy consumption for recirculation, the anode circuit is regularly flushed with fresh hydrogen in a process known as "purge." This involves briefly opening a vent valve, or "purge valve," and introducing a portion of the gas mixture into the cathode exhaust path.

[0006] From a cost and installation space perspective, it is advantageous to use only one jet pump.

[0007] A minimum primary mass flow rate is required for the jet pump to operate correctly; below this minimum primary mass flow rate, subcritical flow rate and recirculation mass flow rate collapse occur.

[0008] One known possibility for extending the operating range of a fuel cell system is to pulse-operate the metering valve, or so-called "hydrogen injector (HGI)," so that the injection pump operates in stages above a minimum mass flow rate and at the same time requires no significantly more hydrogen supply over time compared to that consumed in the fuel cell stack.

[0009] Independent of the switching between metering valves and injection pumps, pulse-controlled metering valves are known in many fuel cell systems. Summary of the Invention

[0010] Within the framework of this invention, a fuel cell system and a method for operating the fuel cell system are proposed. Further features and details of the invention are derived from the various dependent claims, the description, and the drawings. The features and details described herein in conjunction with the method of operation according to the invention also apply to situations associated with the fuel cell system according to the invention, and vice versa, such that disclosures concerning individual aspects of the invention are always mutually referenced or may be mutually referenced.

[0011] This invention is particularly suitable for providing fuel cell systems with high fuel efficiency.

[0012] Therefore, according to the first aspect of the present invention, a fuel cell system for energy conversion is proposed.

[0013] The proposed fuel cell system includes a fuel cell stack, an anode branch for supplying fuel to the fuel cell stack, a vent valve for venting anode gas from the anode branch, a metering valve for dispensing fuel into the anode branch, and a computing unit, wherein the computing unit is configured to pulse-operate the metering valve, and further wherein the computing unit is configured to pulse-operate the vent valve based on the operation of the metering valve.

[0014] In the context of this invention, a computing unit can be understood as a computer, controller, processor, or any other programmable circuit.

[0015] In the context of this invention, a metering valve can be understood as a valve used to dispense fuel into the anode branch, such as a proportional valve.

[0016] In the context of this invention, a vent valve can be understood as a valve used to vent anode gas from the anode branch, such as a so-called "purge valve".

[0017] In the context of this invention, pulse control can be understood as a valve operating mode in which the valve is repeatedly opened and closed regularly, for example at a predetermined frequency, such as between 0.1 Hz and 50 Hz.

[0018] This invention is based on the principle that pulse-controlled metering and venting valves in a fuel cell system minimize fuel loss and maximize fuel efficiency. Therefore, it minimizes fuel concentration in the fuel cell system exhaust and maximizes the safety of the fuel cell system during operation.

[0019] Furthermore, by minimizing water vapor loss, a very dry state in the anode branch can be avoided, thereby maximizing membrane conductivity and thus maximizing the lifespan of the fuel cell system. Accordingly, the present invention can improve lifespan by avoiding dry conditions and achieve efficiency gains through high membrane conductivity.

[0020] By controlling the vent valve according to the control of the metering valve, the nitrogen phase, i.e., a portion of the anode gas containing relatively less fuel than another portion of the anode gas, can be vented, for example, by controlling the vent valve before a certain amount of fuel dispensed to the anode branch through the metering valve reaches the vent valve.

[0021] Alternatively, the relative air humidity in the anode branch can be maximized by controlling the vent valve according to the control of the metering valve, for example by venting a fuel phase, i.e., a portion of the anode gas, which contains relatively more fuel than another portion of the anode gas.

[0022] By determining the time elapsed since the self-metering valve was activated, the current gas composition at the vent valve can be inferred, and the vent valve can be operated accordingly.

[0023] The calculation unit can be configured to operate the relief valve within a certain time range, which is between a first time point and a second time point. At the first time point, the metering valve is operated to dispense fuel into the anode branch at the anode inlet. At the second time point, the fuel concentration at the anode outlet increases in response to the dispensing of fuel through the metering valve.

[0024] By activating the vent valve between a first time point and a second time point, at the first time point, the metering valve is operated to dispense fuel into the anode branch at the anode inlet, and at the second time point, the fuel concentration at the anode outlet increases in response to the fuel dispensed through the metering valve, resulting in minimal fuel discharge by operating the vent valve in a manner that fully utilizes the gaseous travel time of the fuel in the anode branch to activate the vent valve and to release the anode gas from the anode branch for the flushing process, the anode gas moving through the anode branch before the gas phase dispensed through the metering valve.

[0025] It can also be configured that the computing unit is used to determine a second time point based on the gas running time between the anode inlet and the anode outlet in order to minimize fuel loss by manipulating the vent valve.

[0026] Because the gas running time can be changed according to the running point, the second time point can be dynamically determined by the gas running time.

[0027] The calculation unit can be configured to determine a second time point using the length of the gap between the metering valve and the vent valve and the flow velocity of the fuel flowing in the anode branch, wherein the flow velocity is determined with reference to the current operating point of the fuel cell system using a mathematical model of the fuel cell system.

[0028] In the proposed mathematical model of the fuel cell system, for example, temperature and pressure are mathematically mapped according to the operating point. This mathematical model enables the determination of the gas operating time with particular precision, and therefore the determination of a second time point, at which, for example, the vent valve is deactivated, with particular precision.

[0029] It can also be configured that the computing unit is used to determine a second time point based on measurements obtained by a λ sensor at the anode outlet and / or by a hydrogen concentration sensor in the cathode subsystem of the fuel cell system.

[0030] Because the λ sensor quantifies the mass flow rate at the anode outlet, the gas travel time through the anode branch can be directly inferred from the λ sensor's measurements.

[0031] Because the hydrogen concentration sensor in the cathode subsystem of the fuel cell system determines the composition of the gas released through the vent valve, more or less fuel can be released by adjusting the opening duration of the vent valve, for example, based on the measurement value of the hydrogen concentration sensor.

[0032] Alternatively, the computing unit can include a memory storing an allocation scheme that assigns an activation time point for activating the vent valve to the actual operating point of the fuel cell system, and the computing unit is configured to control the vent valve at the time point assigned to the current operating point of the fuel cell system.

[0033] The computational load of the proposed fuel cell system's computational units can be minimized by using an allocation scheme stored in memory.

[0034] It can also be configured that the calculation unit is used to manipulate the metering valve such that the time range of the vent valve activation partially overlaps with the time range of the metering valve activation.

[0035] By overlapping the operation of metering valves and venting valves, very short gas run times or very small nitrogen phases can be covered.

[0036] It can also be configured that the calculation unit is used to control the vent valve within a time range that begins when the fuel concentration at the anode outlet increases and then decreases again in response to the control of the metering valve, in order to minimize water vapor loss by controlling the vent valve.

[0037] By manipulating the vent valve within a timeframe that begins when the fuel concentration at the anode outlet increases and then decreases again in response to the control of the metering valve, the dry fuel phase metered through the metering valve is vented for the flushing process, thus maximizing the wet nitrogen phase in the anode branch.

[0038] It can also be set that the time period for controlling the metering valve is different from the time period for controlling the relief valve.

[0039] By varying the length of the control period, more gas can be released from the anode branch compared to the amount added to the anode branch, or less gas can be released compared to the amount added, for example, only the nitrogen phase flowing before the amount added fuel phase.

[0040] It can also be configured that the computing unit is used to control the vent valve only when the anode gas needs to be vented according to the operating conditions.

[0041] To avoid unnecessary fuel release, the release valve is only operated when release is necessary to operate the fuel cell system, depending on the control of the metering valve.

[0042] According to a second aspect, the present invention relates to an operating method for a fuel cell system, in which a vent valve of one possible configuration of the proposed fuel cell system is pulse-controlled according to the control of a metering valve of the fuel cell system.

[0043] Other advantages, features, and details of the invention will become apparent from the following description, in which embodiments of the invention are described in detail with reference to the accompanying drawings. Herein, the features mentioned in the claims and the description are substantially important to the invention, individually or in any combination. Attached Figure Description

[0044] Figure 1 A schematic diagram of one possible configuration of the proposed fuel cell system. Figure 2 One possible configuration of the proposed method. Figure 3 Another possible configuration of the proposed method. Detailed Implementation

[0045] exist Figure 1 The diagram shows a fuel cell system 100. The fuel cell system 100 includes a fuel cell stack 101, an anode branch 103 for supplying fuel to the fuel cell stack 100, a vent valve 105 for venting anode gas from the anode branch 103, a metering valve 107 for dispensing fuel into the anode branch 103, and a computing unit 109.

[0046] The calculation unit 109 is configured to pulse-operate, for example at a predetermined frequency, the metering valve 107 and, based on the operation of the metering valve 107, pulse-operate, for example at a predetermined frequency, the relief valve 105.

[0047] exist Figure 2 The diagram shows operating method 200. In graph 201, the horizontal axis represents time, and the vertical axis plots the substance content (Stoffmengenanteil) in the anolyte gas.

[0048] The first variation curve 203 represents the fuel material content measured at the anode inlet.

[0049] The second variation curve 205 represents the fuel material content measured at the anode outlet.

[0050] The third variation curve 207 represents the substance content of water measured at the anode inlet.

[0051] The fourth variation curve 209 represents the substance content of water measured at the anode outlet.

[0052] The fifth variation curve 211 represents the nitrogen content measured at the anode inlet.

[0053] The sixth variation curve 213 represents the nitrogen content measured at the anode outlet.

[0054] Bar 215 indicates the control time period for controlling metering valve 109.

[0055] Bar 217 indicates the control time period for operating the relief valve 107.

[0056] The spacing Δt gives the distance between a first time point T1 and a second time point T2, at which the metering valve 107 is operated to dispense fuel into the anode branch at the anode inlet, and at the second time point the fuel concentration at the anode outlet increases as a response to the dispensing of fuel through the metering valve 107.

[0057] Comparing bars 215 and 217 reveals that the control period for the relief valve 105 progresses to the second time point T2 to minimize the release of fuel-containing gas. By disabling the relief valve 105 at the inflection point of the variation curve 205, the release of gas with a high fuel content is avoided, or the gas is simply "purged" until the fuel metered through the metering valve 105 reaches the relief valve 107.

[0058] Accordingly, the discharge of water and nitrogen is maximized by activating the vent valve 107 within the time range of bar 217.

[0059] exist Figure 3 The diagram shows operating method 300. In graph 301, the horizontal axis represents time, and the vertical axis plots the substance content in the anolyte gas.

[0060] The first variation curve 303 represents the fuel substance content measured at the anode inlet.

[0061] The second variation curve 305 represents the fuel substance content measured at the anode outlet.

[0062] The third variation curve 307 represents the water content measured at the anode inlet.

[0063] The fourth variation curve 309 represents the water substance content measured at the anode outlet.

[0064] The fifth variation curve 311 represents the nitrogen content measured at the anode inlet.

[0065] The sixth variation curve 313 represents the nitrogen content measured at the anode outlet.

[0066] Bar 315 specifies the control time period for controlling metering valve 109.

[0067] Bar 317 specifies the control time period for operating the relief valve 105.

[0068] By activating the vent valve 105 within a timeframe that begins after the metering valve 107 is operated and the variation curve 305 rises and then falls again at its inflection point, the leakage of water and nitrogen from the anode branch is minimized and the membrane humidity of the fuel cell system is maximized.

Claims

1. A fuel cell system (100) for energy conversion, wherein, The fuel cell system (100) includes: - Fuel cell stack (101). - An anode branch (103) for supplying fuel to the fuel cell stack (101). - A vent valve (105) for venting anode gas from the anode branch (103). - Metering valve (107) for dispensing fuel into the anode branch (103). - Calculation unit (109). The computing unit (109) is configured to pulse-operate the metering valve (107), and The computing unit (109) is further configured to pulse-operate the relief valve (105) based on the operation of the metering valve (107).

2. The fuel cell system (100) according to claim 1. Its features are, The computing unit (109) is configured to operate the vent valve (105) within a time range between a first time point and a second time point, at the first time point, to operate the metering valve (107) to dispense fuel into the anode branch (103) at the anode inlet, and at the second time point, to increase the fuel concentration at the anode outlet in response to the dispensing of fuel through the metering valve (107).

3. The fuel cell system (100) according to claim 2. Its features are, The computing unit (109) is configured to determine the second time point based on the gas running time between the anode inlet and the anode outlet in order to minimize fuel loss by manipulating the vent valve (105).

4. The fuel cell system (100) according to claim 2 or 3. Its features are, The calculation unit (109) is configured to determine the second time point by means of the length of the gap between the metering valve (107) and the vent valve (105) and the flow rate of the fuel flowing in the anode branch (103), and to determine the flow rate for the current operating point of the fuel cell system (100) by means of a mathematical model of the fuel cell system (100).

5. The fuel cell system (100) according to any one of claims 2 to 4. Its features are, The computing unit (109) is configured to determine the second time point based on measurements obtained by a λ sensor at the anode outlet and / or by a hydrogen concentration sensor in the cathode subsystem of the fuel cell system (100).

6. The fuel cell system (100) according to any one of the preceding claims. Its features are, The computing unit (109) includes a memory storing an allocation scheme that assigns the activation time point for activating the vent valve (105) to the current operating point of the fuel cell system (100). The computing unit (109) is configured to control the vent valve (105) at a time point at the current operating point assigned to the fuel cell system (100).

7. The fuel cell system (100) according to any one of the preceding claims. Its features are, The computing unit (109) is configured to manipulate the metering valve (107) such that the time range of activation of the vent valve (105) partially overlaps with the time range of activation of the metering valve (107).

8. The fuel cell system (100) according to any one of the preceding claims. Its features are, The computing unit (109) is configured to operate the vent valve (105) within a time range that begins when the fuel concentration at the anode outlet decreases again after increasing in response to operating the metering valve (107), in order to minimize water vapor loss by operating the vent valve (105).

9. The fuel cell system (100) according to any one of the preceding claims. Its features are, The time period for controlling the metering valve (107) is different from the time period for controlling the relief valve (105).

10. The fuel cell system (100) according to any one of the preceding claims. Its features are, The computing unit (109) is configured to operate the vent valve (105) only when the anode gas needs to be vented according to the operating conditions.

11. An operating method (200, 300) for a fuel cell system (100), wherein a vent valve (105) of the fuel cell system (100) according to any one of claims 1 to 10 is pulse-controlled according to the control of a metering valve (107) of the fuel cell system (100).

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