Method for determining the state of ageing of the pressure regulator in a fuel cell system

Abstract

The invention proposes a method for operating a fuel cell system (1), in which at least one fuel cell (2) is supplied via an anode gas supply line (3) with an anode gas which is stored in at least one compressed gas container (4) under high pressure, wherein the pressure in the anode gas supply line (3) is set by means of a pressure regulator (5). According to the invention, the following steps are carried out in order to determine the state of ageing of the pressure regulator (5): a) provoking a pressure drop in the anode gas supply line (3) by abruptly increasing the anode gas mass flow in the anode gas supply line (3) such that the pressure in the anode gas supply line (3) drops from an initial pressure (p1) to a defined, lowered pressure (p2), b) restoring the initial pressure (p1) by means of the pressure regulator (5) and determining the time (t) that the pressure regulator (5) requires for restoring the initial pressure (p1), and c) comparing the determined time (t) with at least one reference value (t') which is characteristic of a specific state of ageing of the pressure regulator (5). The invention also relates to a control device which is suitable for carrying out the method according to the invention or individual steps of the method.

Description

[0001] R.416871

[0002] - 1 -

[0003] Description

[0004] Method for operating a fuel cell system; control unit

[0005] The present invention relates to a method for operating a fuel cell system. Furthermore, the invention relates to a control unit suitable for carrying out the method or individual steps of the method.

[0006] State of the art

[0007] Hydrogen-based fuel cells convert hydrogen and oxygen into electrical energy. Heat and water are produced as byproducts of this reaction. Fuel cells have a layered structure with an anode and a cathode, separated by a membrane. During operation, the anode is supplied with hydrogen via an anode circuit, and the cathode is supplied with air as the oxygen source via an air intake path. To increase power output, several fuel cells—often several hundred—are combined in practice to form a fuel cell stack. A fuel cell system can also comprise multiple stacks.

[0008] The hydrogen required by fuel cells is stored under high pressure in at least one pressurized gas cylinder and supplied to the fuel cells via an anode gas supply line. The pressure in the anode gas supply line is regulated by a pressure regulator located downstream of the pressurized gas cylinder, and the pressure level is generally kept constant.

[0009] Since hydrogen is consumed by the electrochemical reaction in the fuel cells, hydrogen must be supplied from at least one pressurized gas container (R.416871).

[0010] - 2 -

[0011] The gas is replenished. At the same time, depleted anode gas is removed from the anode area via a valve, the so-called purge valve.

[0012] The pressure regulator integrated into the anode gas supply line for pressure control is subject to degradation, meaning that its functionality is impaired over time. Furthermore, unforeseen total failures of the pressure regulator can occur.

[0013] The present invention is concerned with the objective of detecting degradation of the pressure regulator as early as possible in order to take appropriate countermeasures if necessary, so that a total failure does not occur.

[0014] To solve the problem, the method with the features of claim 1 is proposed. Advantageous embodiments of the invention are described in the dependent claims. Furthermore, a control unit for executing the method or individual steps of the method is specified.

[0015] Disclosure of the invention

[0016] A method for operating a fuel cell system is proposed, in which at least one fuel cell is supplied with an anode gas via an anode gas supply line. The anode gas is stored under high pressure in at least one pressurized gas container, and the pressure in the anode gas supply line is adjusted by means of a pressure regulator. According to the invention, the following steps are carried out to determine the aging state of the pressure regulator:

[0017] a) Provoking a pressure drop in the anode gas supply line by abruptly increasing the anode gas mass flow rate in the anode gas supply line, so that the pressure in the anode gas supply line falls from an initial pressure p1 to a defined, reduced pressure p2,

[0018] b) Restoring the outlet pressure p1 using the pressure regulator and determining the time t required by the pressure regulator to restore the outlet pressure p1, and R.416871

[0019] - 3 -

[0020] c) Comparing the determined time t with at least one reference value t' that is characteristic of a specific aging state of the pressure regulator.

[0021] The change in the anode gas mass flow leads to a pressure drop in the anode gas supply line. If the output pressure p1 is subsequently restored using the pressure regulator, the time t required for this can be used to determine the aging state of the pressure regulator.

[0022] It is important that the anode gas mass flow rate is increased abruptly, resulting in the desired pressure drop from a defined initial pressure p1 to a defined, reduced pressure p2. This ensures the comparability of the determined time t with the reference value t'. Using the proposed method, the step response of the pressure regulator can thus be evaluated via the induced step function of the mass flow rate.

[0023] Knowing the aging state of the pressure regulator allows for timely countermeasures to be taken to prevent its failure. Furthermore, the need for a pressure regulator replacement can be predicted. Ensuring the pressure regulator's functionality also helps maintain the high efficiency of the fuel cell system.

[0024] The reference value t' used in step c) of the proposed procedure can be a setpoint or output value of the pressure regulator. For example, the determined time t required by the pressure regulator to adjust the pressure in the anode gas supply line to the output pressure p1 can be compared with standard values ​​of a non-degraded pressure regulator. Alternatively or additionally, steps a) to c) can be repeated and the determined time t compared with a previously determined time t as the reference value t'.

[0025] In a further development of the invention, it is therefore proposed that steps a) to c) are repeated at defined time intervals and that at least one R.416871

[0026] - 4 -

[0027] The determined time t is used as a reference value t' in a subsequent repetition of steps a) to c). Using a previously determined time t of the pressure regulator as a reference value t' allows for a more precise determination of the aging state, as the change over time of the determined time t can also be monitored and used to determine the aging state. This allows for more accurate statements about efficiency losses and unplanned failures of the pressure regulator. For example, a disproportionate increase in the determined time t between two repetitions may indicate an impending failure of the pressure regulator.

[0028] Preferably, the determined time t is compared with several previously determined times t and / or the aging state is adjusted with each subsequent determination of time t. In this way, the aging state can be determined more accurately and a failure can be predicted more precisely.

[0029] When repeating steps a) to c), it is important that the times t are determined under substantially identical operating conditions. Therefore, in a further development of the invention, it is proposed that steps a) to c) be repeated under substantially identical operating conditions, in particular with substantially identical anode gas temperature, anode gas composition, and / or substantially identical anode gas upstream pressure of the pressure regulator. The anode gas composition influences the anode gas mass flow rate in the anode gas supply line and thus the step function. The dynamics of the pressure regulator and its step response also depend on the anode gas upstream pressure, i.e., the pressure upstream of the pressure regulator. This applies analogously to the anode gas temperature upstream of the pressure regulator. By using approximately identical operating conditions, the comparability of the determined times t can thus be ensured.

[0030] Alternatively, correction factors can be used to compare times t determined under different operating conditions. These correction factors allow the determined times t to be adjusted so that the times can be compared despite the differing operating conditions. R.416871

[0031] - 5 -

[0032] Furthermore, a limit value is preferably defined for the deviation of the determined time t from at least one reference value t', and if this limit is exceeded, a notification and / or warning signal is issued. In this way, people can be informed early about a defect and / or impending failure of the pressure regulator, thus preventing a failure. In particular, maintenance can be carried out or a workshop can be visited to replace the defective pressure regulator.

[0033] Preferably, a limit value is defined for the deviation of the determined time t from at least one reference value t', and the fuel cell system is shut down if this limit value is exceeded. Shutting down the fuel cell system increases operational safety by preventing further damage to the system. Preferably, the limit value is higher than a first limit value at which only a warning signal is issued.

[0034] Advantageously, in step a), the anode gas mass flow is increased abruptly by opening at least one valve, for example, a purge valve. Anode gas is discharged from the anode area via the open valve without the discharged mass flow being replaced by fresh anode gas. This ultimately leads to the desired pressure drop in the anode gas supply line. The valve can be, in particular, a purge valve, which is typically used to remove anode gas enriched with nitrogen and water from the anode area. In this way, an existing valve can be used.

[0035] Furthermore, a control unit is proposed. The control unit is configured to execute a method according to the invention or individual steps of a method according to the invention. In particular, the control unit can be used to induce a pressure drop in the anode gas supply line by abruptly increasing the anode gas mass flow in the anode gas supply line through the actuation of a valve. Furthermore, the control unit can be used to evaluate the signals from at least one pressure sensor, which monitors the pressure in the anode gas supply line. The control unit thus recognizes when the R.416871

[0036] - 6 -

[0037] The system determines when the pressure in the anode gas supply line has dropped to the defined reduced pressure p2 and how much time t the pressure regulator needs to restore the output pressure p1 in the anode gas supply line. The determined time t can be stored in the control unit so that it can be used as a reference value t'. Alternatively or additionally, at least one reference value t' can be stored in the control unit. The comparison in step c) of the procedure can therefore also be performed using the control unit.

[0038] The invention and its advantages are explained below with reference to the accompanying figure. This figure shows a schematic representation of a fuel cell system that can be operated according to a method according to the invention.

[0039] Detailed description of the drawing

[0040] The figure shows a fuel cell system 1 with two stacks, each comprising several fuel cells 2 in a stacked arrangement. The fuel cells 2 are supplied with hydrogen as anode gas via an anode gas supply line 3. The hydrogen is stored under high pressure in a pressure vessel 4. The pressure vessel 4 is connected to the anode gas supply line 3 via a shut-off valve 6. Hydrogen can be released from the pressure vessel 4 via a drain valve 8 if the temperature and / or pressure in the pressure vessel 4 exceeds a permissible limit. The temperature and pressure are measured and monitored using a temperature sensor 10 and a pressure sensor 11.

[0041] A pressure regulator 5 and, downstream of the pressure regulator 5, another pressure sensor 11 are integrated into the anode gas supply line 3. The pressure regulator 5 reduces the high pressure upstream of the pressure regulator 5 in the anode gas supply line 3 to an intermediate pressure. The intermediate pressure is monitored by the additional pressure sensor 11. Further drain valves 8, the first of which is located upstream, are also used.

[0042] - 7 -

[0043] and another one is located downstream of the pressure regulator 5, the pressure in the anode gas supply line 3 can be reduced if necessary.

[0044] To distribute the anode gas to the two stacks, a gas distributor 9 is integrated into the anode gas supply line 3. Downstream of the gas distributor 9, the anode gas supply line 3 thus forms two branches. A shut-off valve 6 is integrated into each branch, which can be used to switch the respective stack on or off. Downstream of the shut-off valves 6, a further temperature sensor 10 and a pressure sensor 11 are integrated. Anode gas escaping from the stacks, which has become enriched with nitrogen and water, can be removed from the anode area of ​​the respective stack via a purge valve 7.

[0045] During normal operation of the fuel cell system 1, an outlet pressure p1 in the anode gas supply line 3 is set using the pressure regulator 5. Since the pressure regulator 5 degrades with increasing service life, its functionality is impaired, which is particularly evident in the increased control time. This simultaneously reduces the efficiency of the fuel cell system 1. In extreme cases, the pressure regulator 5 and thus the fuel cell system 1 may fail.

[0046] To prevent this, the method according to the invention can be carried out, which provides information about the aging state of the pressure regulator 5. In a first step, a pressure drop is induced in the anode gas supply line 3 by abruptly increasing the anode gas mass flow rate by opening a valve, for example, one of the purge valves 7. The outlet pressure p1 in the anode gas supply line 3 is thereby reduced to a predefined, lowered pressure p2. Subsequently, the outlet pressure p1 is restored using the pressure regulator 5, and the time t required by the pressure regulator 5 for this is determined. By comparing the determined time t with at least one reference value t', the aging state of the pressure regulator 5 can be determined. Knowing the aging state allows for early planning of a replacement of the pressure regulator 5.

[0047] The reference value t' can be a setpoint of the pressure regulator 5. Alternatively, a previously determined value t' can be used.

[0048] - 8 -

[0049] and stored time t is used. For this purpose, the steps described above are repeated at defined time intervals. If the deviation of the determined time t from at least one reference value t' exceeds a predefined limit, a notification and / or warning signal is issued. Alternatively or additionally, the fuel cell system 1 can be switched off if a predefined limit is exceeded.

Claims

R.416871 - 9 - Claims 1. Method for operating a fuel cell system (1) in which at least one fuel cell (2) is supplied via an anode gas supply line (3) with an anode gas which is stored under high pressure in at least one pressure gas container (4), wherein the pressure in the anode gas supply line (3) is adjusted by means of a pressure regulator (5), characterized in that the following steps are carried out to determine the aging state of the pressure regulator (5): a) Provoking a pressure drop in the anode gas supply line (3) by abruptly increasing the anode gas mass flow rate in the anode gas supply line (3), such that the pressure in the anode gas supply line (3) falls from an initial pressure (p1) to a defined, reduced pressure (p2), b) Restoring the outlet pressure (p1) using the pressure regulator (5) and determining the time (t) required by the pressure regulator (5) to restore the outlet pressure (p1), and c) Comparing the determined time (t) with at least one reference value (t') that is characteristic of a certain aging state of the pressure regulator (5).

2. Method according to claim 1 , characterized in that steps a) to c) are repeated at defined time intervals and at least one determined time (t) is used as a reference value (t') in a subsequent repetition of steps a) to c).

3. Method according to claim 2, characterized in that steps a) to c) are carried out under substantially the same operating conditions, in particular at substantially the same anode gas temperature, anode gas composition and / or at imR.416871 - 10 - The process is repeated with essentially the same anode gas pre-pressure upstream of the pressure regulator (5).

4. Method according to any of the preceding claims, characterized in that a limit value is defined for the deviation of the determined time (t) from at least one reference value (t'), when a warning signal and / or indication is issued if this limit is exceeded.

5. Method according to any of the preceding claims, characterized in that a limit value is defined for the deviation of the determined time (t) from at least one reference value (t'), if the fuel cell system (1) is switched off.

6. Method according to any of the preceding claims, characterized in that in step a) the anode gas mass flow is increased abruptly by opening at least one valve (7, 8), for example a purge valve (7).

7. Control unit configured to execute a method or individual steps of a method according to any of the preceding claims.

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