Method for calibrating a device for regulating reflux in a fuel cell system - Patents.com

Abstract

A method for calibrating a device for regulating a return flow (70) in a fuel cell system (1), the fuel cell system (1) comprising a fuel cell stack (101), an air line (10), an exhaust gas line (12) and a fuel line (20) with a recirculation circuit (50), comprising the steps of: a) setting a fixed load point of the fuel cell system (1), b) fixing the flow taken at the fuel cell stack (101), c) activating the device for regulating the return flow (70), so that the exhaust gas flows from the exhaust gas line (12) through the return flow line (66) into the air line (10), d) increasing the mass flow of the exhaust gas flowing through the return flow line (66) via activation of the device for regulating the return flow (70) until a hydrogen concentration is measurable at a hydrogen sensor (64), e) determining the maximum allowable mass flow of exhaust gas through the return flow line (66) for the preselected fixed load point.

Description

[Technical Field]

[0001] The present invention describes a method for calibrating a device for regulating reflux in a fuel cell system. [Background technology]

[0002] Hydrogen-based fuel cell systems are considered a mobility concept for the future, as they emit only water as an exhaust gas and enable fast refueling times. In this case, fuel cell systems require air and hydrogen for the chemical reaction inside the cells. To provide the required amount of energy, several fuel cells arranged in one fuel cell system are wired together to form so-called fuel cell stacks. In this case, the waste heat from the cells is carried away by a cooling circuit and released into the environment. The hydrogen required to operate the fuel cell systems is usually supplied to the systems from a high-pressure tank.

[0003] It is known to direct exhaust gases from the exhaust gas duct of a fuel cell into the air duct, since this naturally brings advantages during certain operating states, for example during a frozen start or during a switch-off process. A corresponding switch-off process is known from DE 10 200 04 11 522 A1. It is also known from DE 10 200 04 11 522 A1 to return exhaust gases to the air duct. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Application with docket number 102018213695.5 [Patent Document 2] Application with docket number 102021205335.1 Summary of the Invention

[0005] The subject of the invention is a method having the features of the independent method claims. Further features and details of the invention are evident from the respective dependent claims, the description and the drawings.

[0006] The method according to the invention comprises the steps of: Determine the maximum allowable mass flow of The method according to the invention provides the advantage that it is possible to determine the maximum possible mass flow or maximum possible feedback rate, and thus achieve feedback of exhaust gases without damaging the fuel cell stack.

[0007] Mixing exhaust gas from the exhaust gas duct into the air in the air duct can be effective under various boundary conditions. A typical operating condition in which feedback of exhaust gas into the air duct can be effective is partial load operation of the fuel cell, where the compressor speed should not fall below a minimum. To reduce the oxygen content of the air supplied to the fuel cell stack via the air duct, exhaust gas can be mixed with oxygen-containing air. In this case, a further positive effect is the humidification of the air by the water in the exhaust gas, which prevents the fuel cell stack from drying out.

[0008] The method according to the invention makes it possible to determine the maximum allowable amount of exhaust gas that can be added to the air without the oxygen content being so low that standard fuel cell operation is impossible across the entire cell, and thus without proton pumping occurring at least in some places.

[0009] If too little oxygen is supplied to the fuel cell stack at one operating point, proton pumping begins because the existing oxygen has already been consumed by the front cells, and no oxygen is now supplied to the rear cells in the fuel cell stack. Because no oxygen is provided, individual hydrogen molecules combine with each other, resulting in H2 within the proton pumping range. This hydrogen is then transported with the exhaust gas in the exhaust gas path and can be detected by a hydrogen sensor.

[0010] Apparatus for regulating reflux in a fuel cell system Determine the maximum allowable mass flow of The method according to the invention, in which the fuel cell system comprises a fuel cell stack, an air channel, an exhaust gas pipe and a fuel pipe with a recirculation circuit, comprises the following method steps: a. of the fuel cell system Steady Load How to set up steps and b. Removed in the fuel cell stack current of Keep constant and method steps; c. A device for adjusting the reflux Control ,the result Exclusion a method step in which gas flows from the exhaust gas pipe through a return pipe into the air duct; d. The mass flow of the exhaust gas flowing through the reflux pipe is adjusted by the device for adjusting the reflux. control increasing the hydrogen concentration until it is measurable by the hydrogen sensor; e. The above-mentioned pre-selected Steady Load determining a maximum allowable mass flow of exhaust gas through the return line for the Contains:

[0011] The dependent claims describe advantageous and further configurations of the method according to the invention.

[0012] of the device for regulating the reflux, which is related to the maximum permissible mass flow Control State It is advantageous to store this value, since it is relatively easy to reproduce.

[0013] During the execution of the method steps, it is advantageous if no purging and / or draining processes are carried out, since these may impair the accuracy of the measurement due to the hydrogen content in the recirculation circuit.

[0014] If the purge and / or drain process has not been stopped, the measurement result should be discarded if necessary by checking whether the purge and / or drain process has been performed when the hydrogen sensor measures the hydrogen concentration. In this case, the existing operating point can be calibrated by performing method steps d.) to e.) again.

[0015] The method according to the invention can be used in particular in fuel cell-powered motor vehicles, but its use in other fuel cell-powered vehicles, such as cranes, ships, rail vehicles, flying vehicles, or stationary objects powered by fuel cells is also conceivable. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of a fuel cell system according to the present invention in accordance with a first embodiment. [Figure 2] FIG. 4 is a schematic diagram of a fuel cell system according to the present invention according to a second embodiment. [Figure 3] 1 is a flow chart of the individual steps of the method according to the invention according to a first embodiment; [Figure 4] 4 is a flow chart of the individual steps of the method according to the invention according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1 shows a schematic topology of a fuel cell system 1 according to a first embodiment of the invention with at least one fuel cell stack 101. The at least one fuel cell system 1 comprises an air line 10, an exhaust gas line 12 and a fuel line 20. The at least one fuel cell stack 101 can be used for mobile applications with high power demands, for example in trucks, or for stationary applications, for example in generators.

[0018] The air channel 10 serves as a supply pipe for supplying air from the surroundings to the cathode 105 of the fuel cell stack 101 via an intake 16. A number of components required for the operation of the fuel cell stack 101 may be arranged in the air channel 10. An air compressor 11 and / or a compressor 11 may be arranged in the air channel 10, which compresses or sucks in the air depending on the respective operating conditions of the fuel cell stack 101. Downstream of the air compressor 11 and / or a compressor 11, a heat exchanger 15 may be located, which heats or cools the air in the air channel 10.

[0019] Other components, such as a filter 7 and / or a humidifier and / or a valve, may be further provided inside the air path 10. Oxygenated air is provided to the fuel cell stack 101 via the air path 10.

[0020] Furthermore, the fuel cell system 1 has an exhaust pipe 12 in which water and other components of the air coming from the air line 10 are transported to the surroundings via an outlet 18 after passing through the fuel cell stack 101. The exhaust gas in the exhaust pipe 12 may contain hydrogen (H2), since some of the hydrogen can diffuse through the membrane of the fuel cell stack 101 or be transported into the exhaust pipe 12 via the purge pipe 40. For this reason, a hydrogen sensor 64 capable of measuring the concentration of hydrogen is provided upstream of the outlet 18.

[0021] A pressure control valve 63 is arranged in the exhaust gas pipe 12, which is able to throttle the flow in the exhaust gas pipe 12, so that different pressures can be set upstream of the pressure control valve 63.

[0022] The fuel cell system 1 may further comprise a cooling circuit designed for cooling the fuel cell stack 101. The cooling circuit is not shown in Figure 1 as it is not part of the present invention.

[0023] At the inlet of the fuel line 20 is a high pressure tank 21 and a shut-off valve 22. Additional components may be located within the fuel line 20 to supply fuel to the anode side 103 of the fuel cell stack 101 as needed.

[0024] To ensure that the fuel cell stack 101 is always adequately fueled, a superstoichiometric delivery of fuel is required through the fuel line 20. Excess fuel, and some amount of water and nitrogen that diffuses through the cell membrane to the anode side, is returned to the recirculation circuit 50 to mix with the fuel delivered through the fuel line 20.

[0025] To promote the flow within the recirculation circuit 50, various components may be installed, such as a jet pump 51 or a blower 52, which are operated with metered fuel. A combination of a jet pump 51 and a blower 52 is also possible.

[0026] The recirculation circuit 50 is connected to the exhaust gas line 12 via a purge line 40 in which a purge valve 41 is arranged to remove unwanted components such as nitrogen or water coming from the recirculation circuit 50. During the purge and / or drain process, the purge valve 41 is opened, so that the gas mixture consisting of unwanted components and hydrogen coming from the recirculation circuit 50 can flow into the exhaust gas line 12.

[0027] The exhaust gas pipe 12 is connected to the air line 10 via a return pipe 66. A device for adjusting the return flow 70 is arranged in the return pipe 66. control In response, the exhaust gas from the exhaust gas pipe 12 can flow into the air duct 10 via the return pipe 66 .

[0028] 1, the device for regulating the return flow 70 is an adjustable valve 71. When the adjustable valve 71 is closed, no exhaust gas from the exhaust gas line 12 flows through the return line 66 into the air line 10. When the adjustable valve 71 is open, the exhaust gas from the exhaust gas line 12 flows through the return line 66 into the air line 10. By changing the opening cross-sectional area of ​​the adjustable valve 71, the mass flow of exhaust gas through the return line 66 can be increased or decreased.

[0029] 2 shows a schematic topology of a fuel cell system 1 according to a second embodiment of the invention. In the second embodiment, the device for regulating the return flow 70 is realized as a blower 72. If the blower 72 is not operating, no exhaust gas flows from the exhaust gas line 12 via the return line 66 into the air line 10. If the blower is operating, the exhaust gas flows from the exhaust gas line 12 via the return line 66 into the air line 10. By changing the rotation speed of the blower 72, the mass flow of exhaust gas through the return line 66 into the air line 10 can be increased or decreased.

[0030] FIG. 3 shows a flow chart of the individual steps of a first embodiment of the method according to the invention for calibrating a device for regulating the reflux 70 in a fuel cell system 1 .

[0031] In the method step 100, a fuel cell system steady load In the fuel cell 101, Current drawn is held constant.

[0032] In method step 200, the purge and / or drain process is interrupted, so that the purge valve 41 cannot be opened during the method according to the invention.

[0033] In method step 300, a device for adjusting reflux 70 is provided. control As a result, exhaust gas can flow from the exhaust pipe 12 through the return pipe 66 into the air duct 10, or the mass flow from the exhaust pipe 12 through the return pipe 66 into the air duct 10 is increased.

[0034] In method step 400, it is checked whether the hydrogen concentration can be measured by the hydrogen sensor 64. If not, method step 300 is started again to check the hydrogen concentration of the device for adjusting the reflux 70. control 66 into the air passage 10 from the exhaust gas pipe 12.

[0035] If the hydrogen concentration can be measured by the hydrogen sensor 64 in method step 400, the current mass flow is calculated based on the previously selected Steady-state load point Alternatively, to prevent proton pumping from occurring in the rear region of the cells of the fuel cell stack 101, the present mass flow is selected as the maximum allowable mass flow of the exhaust gas through the return line 66. lower The mass flow may be selected as the maximum allowable mass flow.

[0036] FIG. 4 shows a flow chart of the individual steps according to a second embodiment of the method according to the invention for calibrating a device for regulating the reflux 70 in a fuel cell system 1 .

[0037] In the method step 100, a fuel cell system At the steady load point In the fuel cell 101, Current drawn is kept constant. Current drawn The measure to keep constant can also be expressed as follows: current From method step 100, method step 300 is directly followed.

[0038] In method step 300, a device for regulating reflux 70 is provided. control As a result, exhaust gas can flow from the exhaust pipe 12 through the return pipe 66 into the air duct 10, or the mass flow from the exhaust pipe 12 through the return pipe 66 into the air duct 10 is increased.

[0039] In method step 400, it is checked whether the hydrogen concentration can be measured by the hydrogen sensor 64. If not, method step 300 is started again to check the hydrogen concentration of the device for adjusting the reflux 70. control 66 into the air passage 10 from the exhaust gas pipe 12.

[0040] If, in method step 400 , the hydrogen concentration can be measured by the hydrogen sensor 64 , method proceeds to method step 450 .

[0041] In method step 450, it is determined whether a purge and / or drain process has been performed. If so, the measurement results are discarded and method step 470 is continued; otherwise, method step 500 is continued.

[0042] In method step 470, after the purge and / or drain process has ended, the mass flow through the return line 66 is reduced and method step 300 is started again.

[0043] In method step 500, the current mass flow is calculated based on a preselected Steady-state load point Alternatively, to prevent pumping in the rear region of the cells of the fuel cell stack 101, the present mass flow is selected as the maximum allowable mass flow of the exhaust gases through the return line 66. lower The mass flow may be selected as the maximum allowable mass flow. [Explanation of symbols]

[0044] 1. Fuel cell system 10 Airway 11 Air Compressor 12 Exhaust gas pipe 20 Fuel pipe 50 Recirculation circuit 64 Hydrogen Sensor 66 Reflux pipe 70 reflux 71 Adjustable valve 72 Blower 101 Fuel Cell Stack

Claims

1. A method for determining the maximum permissible mass flow of a device for regulating the reflux (70) in a fuel cell system (1), said fuel cell system (1) comprising a fuel cell stack (101), an air channel (10), an exhaust gas pipe (12) and a fuel pipe (20) with a recirculation circuit (50), said method comprising the following method steps: a first method step of setting a constant load on the fuel cell system (1) to keep the current drawn by the fuel cell stack (101) constant; a second method step, after the first method step, of controlling the device for regulating the reflux (70) so that exhaust gas flows from the exhaust gas pipe (12) through the reflux pipe (66) into the air duct (10); a third method step, after the second method step, of increasing the mass flow of the exhaust gas through the reflux line (66) by controlling the device for regulating the reflux (70) until hydrogen is detected by a hydrogen sensor (64) provided in the exhaust gas line (12); a fourth method step, after the third method step, of determining the current exhaust gas mass flow or a mass flow lower than the current exhaust gas mass flow as the maximum permissible exhaust gas mass flow through the return line (66) for the steady-state load; How to implement this.

2. 2. The method according to claim 1, characterized in that in the fourth method step, the control state of the device for regulating the reflux (70) is stored, which is related to the maximum allowable mass flow.

3. 2. The method according to claim 1, wherein during the third method step, no purging and / or draining process is carried out for discharging the gas mixture consisting of unwanted components and hydrogen coming from the recirculation circuit (50) into the exhaust gas pipe (12).

4. 2. The method according to claim 1, further comprising the step of: if hydrogen is detected by the hydrogen sensor (64) in the third method step, checking whether a purge and / or drain process has been carried out to discharge a gas mixture consisting of hydrogen and unwanted components coming from the recirculation circuit (50) into the exhaust gas pipe (12); and if so, discarding the detection result, so that the fourth method step is not carried out.

5. A method as described in claim 4, characterized in that following the third method step, after the purging process and / or draining process is completed, the mass flow through the reflux pipe (66) is reduced and the third method step is carried out again.

6. 6. The method according to claim 1, wherein the device for adjusting the return flow (70) is an adjustable valve (71), and the mass flow of the exhaust gas through the return line (66) is increased by enlarging the opening cross-sectional area of ​​the adjustable valve (71).

7. 6. The method according to claim 1, wherein the device for adjusting the reflux (70) is a blower (72), and the mass flow of the exhaust gases through the reflux line (66) is increased by increasing the rotation speed of the blower (72).

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