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 an apparatus for regulating reflux in a fuel cell system. [Background technology]

[0002] Hydrogen-based fuel cell systems are considered a mobility concept of the future, as they emit only water as an exhaust gas and allow for fast refueling times. In this case, they require air and hydrogen for the chemical reaction in the cell. To provide the required amount of energy, several fuel cells arranged in one fuel cell system are wired together to form a so-called multiple fuel cell stack. In this case, the waste heat of the cell is carried away by a cooling circuit and released to the environment. The hydrogen required to operate the fuel cell system 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 leads to advantages in certain operating states, for example during freeze-start or during switch-off processes. Corresponding switch-off processes are known from DE 10 200 03 133 A1. It is also known from DE 10 200 03 133 A1 to return exhaust gases into 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 with the features of the independent method claim. 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 is used to provide a method for calibrating a device for adjusting the return flow in a fuel cell system. The method according to the invention offers the advantage that the maximum possible mass flow or the maximum possible feedback rate can be determined, so that the feedback of exhaust gases can be achieved without damaging the fuel cell stack.

[0007] The mixing of 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 the feedback of exhaust gas into the air duct can be effective is the partial load operation of the fuel cell, where the compressor speed should not fall below a minimum speed. In order to reduce the oxygen content of the air supplied to the fuel cell stack via the air duct, the exhaust gas can be mixed into the oxygen-containing air. In this case, a further positive effect is the humidification of the air by the water in the exhaust gas, so that drying out of the fuel cell stack can be avoided.

[0008] The method according to the invention makes it possible to determine the maximum permissible amount of exhaust gas that can be fed 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 the rear cells in the fuel cell stack are no longer supplied with any oxygen at all. As no oxygen is provided, the 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] A method according to the invention for calibrating a device for regulating a reflux in a fuel cell system, the fuel cell system having a fuel cell stack, an air line, an exhaust gas line and a fuel line with a recirculation circuit, comprises the following method steps: a. method steps of setting a fixed load point of the fuel cell system; b. method steps of fixing a flow extracted in the fuel cell stack; c. activating a device for regulating the reflux, so that the exhaust gas flows from the exhaust gas line through a reflux line into the air line; d. increasing the mass flow of the exhaust gas flowing through the reflux line via activation of the device for regulating the reflux until a hydrogen concentration is measurable by a hydrogen sensor; e. determining a maximum allowable mass flow of exhaust gas through said return line for said preselected fixed load point; Contains:

[0011] Advantageous and further configurations of the method according to the invention are described in the dependent claims.

[0012] It is advantageous if the activation of the device for regulating the reflux, which is related to the maximum permissible mass flow, is stored, since this value is relatively easily reproducible.

[0013] During the performance of several method steps, it is advantageous if no purge and / or drain procedures are carried out, since these can impair the accuracy of the measurement due to the hydrogen content in the recirculation circuit.

[0014] If the implementation of the purge and / or drain process has not been stopped, it is necessary to check whether a purge and / or drain process has been carried out when the hydrogen sensor measures a hydrogen concentration, and if so, to discard the measurement result. In this case, a calibration of the existing operating point is possible by carrying out 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 also in other fuel cell powered mobile means, such as, for example, cranes, ships, rail vehicles, flying vehicles, or in stationary objects powered by fuel cells. [Brief description 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; [Diagram 2] FIG. 4 is a schematic diagram of a fuel cell system according to the present invention according to a second embodiment. [Diagram 3] 2 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 PREFERRED EMBODIMENTS

[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 demand, e.g. in trucks, or for stationary applications, e.g. in generators.

[0018] The air duct 10 serves as a supply line for supplying air from the surroundings via an intake 16 to the cathode 105 of the fuel cell stack 101. A number of components required for the operation of the fuel cell stack 101 may be arranged in the air duct 10. An air compressor 11 and / or a compressor 11 may be arranged in the air duct 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 the compressor 11 there may be a heat exchanger 15, which heats or cools the air in the air duct 10.

[0019] Further components, such as, for example, a filter 7 and / or a humidifier and / or a valve, may be provided inside the air path 10. Via the air path 10, oxygen-containing air is provided to the fuel cell stack 101.

[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 be diffused by the membrane of the fuel cell stack 101 or is transported into the exhaust pipe 12 via the purge pipe 40. For this reason, a hydrogen sensor 64 is provided upstream before the outlet 18, which can measure the concentration of hydrogen.

[0021] In the exhaust gas pipe 12 a pressure control valve 63 is arranged 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 since it is not part of the invention.

[0023] At the inlet of the fuel line 20 is a high pressure tank 21 and a shutoff valve 22. Further 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] In order to always adequately fuel the fuel cell stack 101, there is a need for superstoichiometric dosing of fuel through the fuel line 20. Excess fuel, and some amount of water and nitrogen that diffuses through the cell membrane to the anode side, are returned into the recirculation circuit 50 to mix with the fuel dispensed from the fuel line 20.

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

[0026] To remove unwanted components such as nitrogen or water coming from the recirculation circuit 50, 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. 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 line 12 is connected to the air line 10 via a return line 66. A device for adjusting the return flow 70 is arranged in the return line 66. Upon activation of the device for adjusting the return flow 70, exhaust gas from the exhaust gas line 12 can flow via the return line 66 into the air line 10.

[0028] According to the first embodiment of Fig. 1, the device for regulating the return flow 70 is an adjustable valve 71. If the adjustable valve 71 is closed, no exhaust gas from the exhaust gas line 12 flows via the return line 66 into the air line 10. If the adjustable valve 71 is open, the exhaust gas from the exhaust gas line 12 flows via 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 activated, no exhaust gas flows from the exhaust gas line 12 via the return line 66 into the air line 10. If the blower is activated, 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 a method according to the invention for calibrating a device for regulating the return flow 70 in a fuel cell system 1 .

[0031] In method step 100, a fixed load point of the fuel cell system is set to keep the flow extracted at the fuel cell 101 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 the return flow 70 is activated so that exhaust gas can flow from the exhaust gas pipe 12 through the return flow line 66 into the air line 10, or the mass flow flowing from the exhaust gas pipe 12 through the return flow line 66 into the air line 10 is increased.

[0034] In method step 400, it is checked whether the hydrogen concentration can be measured by the hydrogen sensor 64. If this is not possible, method step 300 is started again and the mass flow from the exhaust gas line 12 through the return line 66 into the air line 10 is increased by activating a device for adjusting the return flow 70.

[0035] If in method step 400 the hydrogen concentration can be measured by the hydrogen sensor 64, then proceed to method step 500, where the current mass flow is selected as the maximum allowable mass flow of exhaust gas through the return line 66 for a preselected fixed load point. Alternatively, a mass flow downstream of the current mass flow may be selected as the maximum allowable mass flow in order to prevent proton pumping in the rear region of the cells of the fuel cell stack 101.

[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 return flow 70 in a fuel cell system 1 .

[0037] In method step 100, a fixed load point of the fuel cell system is set to keep the extracted flow constant at the fuel cell 101. The measure of keeping the extracted flow constant at the fuel cell 101 can also be described in the following expression: fix the extracted flow at the fuel cell stack 101. From method step 100 one proceeds directly to method step 300.

[0038] In method step 300, a device for adjusting the return flow 70 is activated so that exhaust gas can flow from the exhaust gas pipe 12 through the return flow line 66 into the air line 10, or the mass flow flowing from the exhaust gas pipe 12 through the return flow line 66 into the air line 10 is increased.

[0039] In method step 400, it is checked whether the hydrogen concentration can be measured by the hydrogen sensor 64. If this is not possible, method step 300 is started again and the mass flow from the exhaust gas line 12 through the return line 66 into the air line 10 is increased by activating a device for adjusting the return flow 70.

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

[0041] Method step 450 checks whether a purge and / or drain process has been performed. If so, discard the measurement results and proceed to method step 470; otherwise, proceed to method step 500.

[0042] In method step 470, after the purge and / or drain process has been completed, 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 selected as the maximum allowable mass flow of exhaust gas through the return line 66 for a preselected fixed load point. Alternatively, a mass flow downstream of the current mass flow may be selected as the maximum allowable mass flow to prevent pumping in the rear region of the cells of the fuel cell stack 101. [Explanation of symbols]

[0044] 1. Fuel cell system 10 Air passage 11 Air Compressor 12 Exhaust gas pipe 20 Fuel pipe 50 Recirculation circuit 64 Hydrogen Sensor 66 Reflux tube 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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