WO2023117382A1

WO2023117382A1 - Method for operating a fuel cell system, and fuel cell system

Info

Publication number: WO2023117382A1
Application number: PCT/EP2022/084342
Authority: WO
Inventors: Helerson Kemmer
Original assignee: Robert Bosch Gmbh
Priority date: 2021-12-20
Filing date: 2022-12-05
Publication date: 2023-06-29
Also published as: DE102021214693A1

Abstract

The invention relates to a method for operating a fuel cell system (1) having multiple fuel cell stacks (100, 200) which each have a cathode (110, 210) and an anode (120, 220), the cathodes (110, 210) each being supplied with air via a feed air path (111, 211), and exhaust air emitted from the fuel cell stacks (100, 200) being discharged via an exhaust air path (112, 212), and the anodes (120, 220) each being supplied with hydrogen via an anode circuit (121, 221). According to the invention, a previously inertised anode (220) of at least one fuel cell stack (200) is filled with hydrogen on starting, wherein predominantly inert anode gas present in the anode circuit (221) is removed from the anode circuit (221) via a connecting line (2) which has an integrated shut-off valve (3) and connects the anode circuit (221) to an exhaust air path (112) of a further fuel cell stack (100), and is introduced into the exhaust air path (112) of the further fuel cell stack (100). The invention further relates to a fuel cell system (1) for carrying out the method.

Description

Method for operating a fuel cell system, fuel cell system

The invention relates to a method for operating a fuel cell system having the features of the preamble of claim 1. The invention also relates to a fuel cell system which is suitable for carrying out the method or can be operated according to the method.

Preferred areas of application are fuel cell vehicles, preferably fuel cell vehicles with start-stop operation.

State of the art

Fuel cells are electrochemical energy converters. In particular, hydrogen (H2) and oxygen (O2) can be used as reaction gases. These are converted into electrical energy, water (H2O) and heat with the help of a fuel cell. The core of a fuel cell is formed by a membrane-electrode assembly (MEA), which comprises a membrane that is coated on both sides with a catalytic material to form electrodes. During operation of the fuel cell, hydrogen is supplied to one electrode, the anode, and oxygen is supplied to the other electrode, the cathode.

In order to increase the electrical power, in practice a large number of fuel cells are connected to form a fuel cell stack or stack. In addition, several fuel cell stacks or fuel cell systems can be interconnected.

In the operation of a fuel cell system, the start and/or stop phases represent a high load, which can lead to degradation of the fuel cells. At startup, the primary cause of this is a hydrogen-air front in the anode. When stopping or switching off, there is a high voltage that is caused by the fact that the anode is filled with hydrogen and the cathode with oxygen be supplied without an electrical load being pulled from the stack. This can occur in particular during long shutdown phases.

In order to counteract the degradation of the fuel cells in a start and/or stop phase, the oxygen present in the cathode can be consumed before the system is shut down by drawing electrical current without additional air supply. Meanwhile, the anode continues to be supplied with hydrogen, so that the cell voltages are not critical. However, if air diffuses into the cathode, cell voltages increase and remain there for several hours, causing damaging electrochemical reactions. As a rule, shut-off valves are therefore provided on both the inlet and outlet sides, which are intended to prevent air from getting into the cathode in the event of a shutdown. However, since these are not completely sealed, especially over their lifetime, their effectiveness is limited. Furthermore, the shut-off valves are accompanied by a not insignificant loss of pressure.

It is known from stationary applications to render the anode and, if necessary, the cathode inert with nitrogen before starting and/or shutting down in order to counteract undesirable degradation. For this purpose, the nitrogen is kept in a bottle. In mobile applications, however, this is often not possible for reasons of space. Furthermore, a nitrogen bottle has to be refilled and serviced, which has a negative impact on costs.

An electrochemically neutral and thus degradation-free state can be produced in the anode and/or cathode during a shutdown phase by inerting. When restarting, the anode and/or cathode must then be refilled with the respective gas. When filling the anode with hydrogen, this does not lead to any degradation if the anode has been rendered inert beforehand. However, when filling with hydrogen, the inert anode gas must be discharged at the same time. Since this can still contain hydrogen, there is a risk that an explosive gas mixture will form. This must be prevented.

The present invention is concerned with the task of counteracting the degradation of fuel cells in a fuel cell system with a plurality of fuel cell stacks. To solve the problem, the method with the features of claim 1 is proposed. Advantageous embodiments can be found in the dependent claims. In addition, a fuel cell system is specified which is suitable for carrying out the method or can be operated according to the method.

Disclosure of Invention

A method for operating a fuel cell system with a plurality of fuel cell stacks, each of which has a cathode and an anode, is proposed. Air is supplied to the cathodes in each case via an air supply path, and exhaust air exiting from the fuel cell stacks is discharged in each case via an exhaust air path. The anodes are each supplied with hydrogen via an anode circuit. According to the invention, a previously inerted anode of at least one fuel cell stack is filled with hydrogen when it is started, with the predominantly inert anode gas present in the anode circuit being removed from the anode circuit via a connecting line with an integrated shut-off valve, which connects the anode circuit to an exhaust air path of another fuel cell stack, and fed into the exhaust air path of the further fuel cell stack is initiated.

The anode gas can be diluted by introducing the anode gas removed from the anode circuit into the exhaust air path of a further fuel cell stack. Because - as already mentioned - the anode gas can contain residues of hydrogen, so that the dilution ensures that no explosive gas mixture leaves the fuel cell system.

Because the anode has previously been rendered inert, the degradation of the fuel cell stack can also be counteracted. Consequently, the service life of the at least one fuel cell stack can be increased with the aid of the proposed method.

While the anode of the at least one fuel cell stack is being filled with hydrogen, the cathode of the same fuel cell stack preferably (still) contains inert gas. Degradation is then excluded. At the same time, shut-off valves provided in the supply air and/or exhaust air path of the cathode can be omitted, so that it is not the case at the outset mentioned pressure drop. In this way, hydrogen consumption can be reduced at the same time.

The method step of filling the anode of at least one fuel cell stack with hydrogen is therefore preceded by the method step of rendering the anode inert. This method step can also be carried out when the fuel cell stack or the fuel cell system is started or already when it is shut down.

The anode of at least one fuel cell stack is preferably rendered inert before being filled with hydrogen using the exhaust air from another fuel cell stack, which is started or continues to be operated for this purpose. Since the exhaust air from a fuel cell stack is oxygen-free or at least low in oxygen, it can be used as an inert gas to render the anode of another fuel cell stack inert. The provision of an inert gas in a separate tank and the regular filling and maintenance of the tank can thus be omitted. Instead, inert gas that is already present in the system is used. The method is therefore particularly suitable for operating mobile fuel cell systems.

Analogously, the cathode of at least one fuel cell stack can be rendered inert before being filled with hydrogen using the exhaust air from another fuel cell stack, which is started or continues to be operated for this purpose.

Furthermore, the hydrogen required for filling is preferably taken from a tank and introduced into the anode circuit of an anode to be filled with the aid of a metering valve. With the help of the metering valve, which is preferably designed as a proportional valve, the amount of hydrogen introduced and the pressure in the anode circuit can be controlled or regulated.

Furthermore, a purge valve and/or drain valve integrated into the anode circuit is or are preferably kept closed during the filling of the anode with hydrogen. This ensures that predominantly inert anode gas present in the anode circuit is not discharged via the purge and/or drain valve but via the shut-off valve integrated in the connecting line and introduced into the exhaust air path of the other fuel cell stack becomes. Flushing quantities occurring during normal operation of the fuel cell stack or fuel cell system can be discharged in the usual way via the purge and/or drain valve.

During the filling of the anode with hydrogen, a fan integrated into the anode circuit is advantageously switched on for active circulation of the anode gas present in the anode circuit. The filling of the anode with hydrogen can be accelerated in this way.

It is also proposed that the air mass flow in the supply air path of the other fuel cell stack is increased while the anode is being filled with hydrogen. This is because the consequence of this is that the exhaust air mass flow in the exhaust air path of the fuel cell stack increases. This means that anode gas introduced into the exhaust air path from another fuel cell stack whose anode is currently being filled with hydrogen is diluted even better or more strongly.

In addition, a fuel cell system with a plurality of fuel cell stacks is proposed to solve the task mentioned at the outset. The multiple fuel cell stacks each have a cathode and an anode. The cathodes are each connected to a supply air path on the inlet side and to an exhaust air path on the outlet side. The anodes are each connected to an anode circuit. According to the invention, the anode circuit of at least one fuel cell stack is connected to the exhaust air path of another fuel cell stack via a connecting line with an integrated shut-off valve.

The proposed fuel cell system is particularly suitable for carrying out the method according to the invention described above or can be operated according to this method, so that the same advantages are achieved. In particular, the formation of an explosive gas mixture can be prevented when removing anode gas from a previously inerted anode of a fuel cell stack, since the anode gas mixes with the exhaust air from the other fuel cell stack and is thereby diluted.

A preferred embodiment of the invention is explained in more detail below with reference to the accompanying drawings. These show: Figure 1 is a schematic representation of a fuel cell system according to the invention and

FIG. 2 shows the sequence of a method according to the invention, according to which the fuel cell system of FIG. 1 can be operated.

Detailed description of the drawings

Figure 1 shows a fuel cell system 1 according to the invention with a first fuel cell stack 100 and a second fuel cell stack 200.

The fuel cell stacks 100, 200 each have a cathode 110, 210 and an anode 120, 220. The cathodes 110, 210 are supplied with air as an oxygen supplier via an air supply path 111, 211. The air is taken from the environment and fed via an air filter 114, 214 to an air delivery and air compression system 113, 213 in order to provide a certain air mass flow and a certain pressure level. Since the air is heated in the process, it is cooled with the aid of a heat exchanger 115, 215 integrated into the supply air path 111, 211. The exhaust air from the fuel cell stack 100, 200 is discharged via an exhaust air path 112, 212 in each case. A pressure control valve 130, 230 is integrated in each case in the exhaust air path 112, 212. To bypass the fuel cell stack 100, 200, the air supply paths 111, 211 and the exhaust air paths 112, 212 can be connected via a bypass path 118, 218 with an integrated bypass valve 119, 219.

The cathode 110 of the fuel cell stack 100 can be separated from the supply air path 111 and from the exhaust air path 112 by means of shut-off valves 117, so that the air supply to the cathode 110 can be interrupted via this. The further fuel cell stack 200 does not require such shut-off valves.

The anodes 120, 220 of the two fuel cell stacks 100, 200 are each supplied with fresh anode gas or hydrogen and with recirculated anode gas via an anode circuit 121, 221. The recirculation is effected passively with the aid of a jet pump 124, 224 and actively with the aid of a blower 123, 223. Since over time the recirculated anode gas is enriched with nitrogen, which diffuses from the cathode side to the anode side Anode circuit 121, 221 each have a purge valve 122, 222 provided. By opening the purge valve 122, 222, nitrogen-containing anode gas is discharged from the anode circuit 121, 221 and replaced by hydrogen from a tank (132, 232) via a metering valve (131, 231) that is opened at the same time. A pressure regulator 125, 225 is arranged downstream of the metering valve 131, 231 in each case. Since the recirculated anode gas is also enriched with water, a water separator 126, 226 with a container 127, 227 is also integrated into the anode circuit 121, 221 in each case. By opening a drain valve 128, 228, the container 127, 227 can be emptied from time to time.

The heat generated during operation of the fuel cell stack 100, 200 is dissipated with the aid of a cooling circuit 129, 229 in each case.

The anode circuit 221 of the fuel cell stack 200 is connected or can be connected to the exhaust air path 112 of the fuel cell stack 100 via a connecting line 2 with an integrated shut-off valve 3 . When the shutoff valve 3 is open, anode gas can thus be introduced from the anode circuit 221 of the fuel cell stack 200 into the exhaust air path 112 of the fuel cell stack 100 .

When starting, the fuel cell system 1 shown in FIG. 1 can therefore be operated according to the method shown in FIG. 2, which is described below.

The starting process is initiated in step S10 of the method illustrated in FIG. For this purpose, the fuel cell stack 100 is first put into operation in step Sil, so that air ("Lz", see Figure 1) is supplied to it via the air supply path 111, which then reaches the exhaust air path 112 as oxygen-free or at least low-oxygen exhaust air. This can then be used in step S12 to render the anode 220 and preferably the cathode 210 of the further fuel cell stack 200 inert.

In step S13, the purge valve 222 and/or the drain valve 228 of the further fuel cell system 200 is or are closed if it is open. Subsequently, in step S14, with the metering valve 231 open, the anode 220 of the fuel cell stack 200 is filled with hydrogen from the tank 232. At the same time, the fan 223 can be put into operation to increase the circulation ("Z", see Figure 1) in the anode circuit 221 to promote. In order to increase the exhaust air mass flow in the exhaust air path 112 of the first fuel cell stack 100, the speed of the air delivery and air compression system 113 of the first fuel cell stack 100 arranged in the intake air path 111 can be increased in a step S15. This is then done in step S16

Shutoff valve 3 is opened, so that anode gas flows from the anode circuit 221 of the other fuel cell stack 200 via the connecting line 2 into the exhaust air path 112 of the first fuel cell stack 100 ("AG", see Figure 1) and the anode circuit 221 is filled with fresh hydrogen from the tank 232 . In step S17 it is then checked whether the anode circuit 221 has been completely flushed or refilled. If "yes", the start-up process is ended in step S18.

The anode gas ("AG", see FIG. 1) introduced into the exhaust air path 112 of the first fuel cell stack 100 is removed from the fuel cell system 1 via the exhaust air path 112 together with the exhaust air ("LA", see FIG. 1) present there.

Claims

- 9 - Claims

1. A method for operating a fuel cell system (1) with a plurality of fuel cell stacks (100, 200), each having a cathode (110, 210) and an anode (120, 220), the cathodes (110, 210) each having a supply air path (111, 211) air is supplied and exhaust air exiting the fuel cell stacks (100, 200) is discharged via an exhaust air path (112, 212), and wherein the anodes (120, 220) each have an anode circuit (121, 221). are supplied with hydrogen, characterized in that a previously inerted anode (220) of at least one fuel cell stack (200) is filled with hydrogen when it is started, the predominantly inert anode gas present in the anode circuit (221) being discharged via a connecting line (2) with an integrated shut-off valve (3rd ) which connects the anode circuit (221) to an exhaust air path (112) of a further fuel cell stack (100), is removed from the anode circuit (221) and introduced into the exhaust air path (112) of the further fuel cell stack (100).

2. The method according to claim 1, characterized in that the anode (220) of at least one fuel cell stack (200) is rendered inert prior to being filled with hydrogen using the exhaust air from another fuel cell stack (100) which is started or continues to be operated for this purpose.

3. The method according to claim 1 or 2, characterized in that the cathode (210) of at least one fuel cell stack (200) is rendered inert before being filled with hydrogen using the exhaust air from another fuel cell stack (100) which is started for this purpose or is further operated.

4. The method according to any one of the preceding claims, characterized in that the hydrogen required for filling is taken from a tank (232) and introduced into the anode circuit (221) of an anode (220) to be filled with the aid of a metering valve (231).

5. The method according to any one of the preceding claims, characterized in that while the anode (220) is being filled with hydrogen, a purge valve (222) and/or drain valve (228) integrated into the anode circuit (221) is or are kept closed.

6. The method according to any one of the preceding claims, characterized in that during the filling of the anode (220) with hydrogen in the anode circuit (221) integrated fan (223) for active circulation of the anode circuit (221) present anode gas is switched on.

7. The method according to any one of the preceding claims, characterized in that the air mass flow in the supply air path (111) of the other fuel cell stack (100) is increased during the filling of the anode (220) with hydrogen, so that the exhaust air mass flow in the exhaust air path (112) increases.

8. Fuel cell system (1) with a plurality of fuel cell stacks (100, 200), each having a cathode (110, 210) and an anode (120, 220), the cathodes (110, 210) each having an inlet air path (111, 211) and are connected to an exhaust air path (112, 212) on the outlet side, and the anodes (120, 220) are each connected to an anode circuit (121, 221), characterized in that the anode circuit (221) of at least one fuel cell stack (200 ) is connected via a connecting line (2) with an integrated shut-off valve (3) to the exhaust air path (112) of a further fuel cell stack (100).