Method for Compensating for a Temperature-Induced Rise in Pressure in an Anode Section of a Fuel-Cell System

Abstract

A method for at least partially compensating for a temperature-induced rise in pressure in a fuel-cell system includes providing a fuel-cell system that has an anode supply path that establishes a fluidic connection between a fuel-cell stack and at least one fuel-source, and an anode-side stack shut-off valve in the anode supply path, the anode-side stack shut-off valve prohibiting the supply of fuel to the fuel-cell stack from an anode section of the anode supply path. The fuel-cell system also has an excess-pressure valve in the anode section, the excess-pressure valve conducting fuel away out of the anode section if the pressure in the anode section exceeds a tripping pressure. In the shut-down state, the pressure in the anode section rises due to warming of the fuel. The anode-side stack shut-off valve is opened to relieve the pressure before the rising pressure in the anode section reaches the tripping pressure.

Claims

1-15. (canceled)

16. A method for at least partially compensating for a temperature-induced rise in pressure in a fuel-cell system, comprising: providing a fuel-cell system, including: an anode supply path that establishes a fluidic connection between a fuel-cell stack and at least one fuel-source, an anode-side stack shut-off valve in the anode supply path, wherein the anode-side stack shut-off valve is configured to prohibit the supply of fuel to the fuel-cell stack from an anode section of the anode supply path, and an excess-pressure valve in the anode section, wherein the excess-pressure valve is configured to conduct fuel away out of the anode section if the pressure in the anode section exceeds a tripping pressure, wherein, in the shut-down state of the fuel-cell system, the pressure in the anode section rises by reason of a warming of the fuel; and opening the anode-side stack shut-off valve so as to relieve the pressure before the rising pressure in the anode section reaches the tripping pressure of the excess-pressure valve.

17. The method of claim 16, wherein the stack shut-off valve is open for the purpose of pressure relief for less than 10 seconds or less than 1 second or less than 100 milliseconds.

18. The method of claim 16, wherein the stack shut-off valve is opened for the purpose of pressure relief after a defined first period of time has elapsed from the time starting from which the fuel-cell system assumed the shut-down state.

19. The method of claim 16, wherein several pressure-relief operations are undertaken during the warming of the fuel.

20. The method of claim 19, wherein the period of time between a first pressure relief and a second pressure relief is a second period of time, and wherein the second period of time is longer than the first period of time.

21. The method of claim 20, wherein the first period of time and/or the second period of time amount(s) to between 3 minutes and 20 minutes or between 5 minutes and 10 minutes.

22. The method of claim 20, wherein the first period of time and/or the second period of time is/are defined on the basis of an ambient-temperature value that is indicative of the temperature in the immediate vicinity of the warming anode section.

23. The method of claim 20, wherein the first period of time and/or the second period of time is/are defined on the basis of a fuel-temperature value that is indicative of the fuel temperature in the anode section (MD).

24. The method of claim 20, wherein the first period of time and/or the second period of time is/are defined by a characteristic map saved in the fuel-cell system, and wherein various values for the period of time are stored in the characteristic map, each of which depends on: (a) an ambient-temperature value, (b) a fuel-temperature value, and/or (c) an initial pressure value that is indicative of an initial pressure in the anode section at the time at which the fuel-cell system assumed the shut-down state.

25. The method of claim 24, wherein the first period of time, the second period of time, the fuel-temperature value, the ambient-temperature value and/or the initial pressure value are determined during the shutting down of the fuel-cell system.

26. The method of claim 20, wherein a control unit of the fuel-cell system is inactive during the first period of time and/or the second period of time, and wherein the control unit is activated for the purpose of pressure relief.

27. The method of claim 16, further comprising: registering a pressure value that is indicative of the current pressure in the anode section during the warming of the fuel in the shut-down state of the fuel-cell system; and opening the anode-side stack shut-off valve if the registered pressure value in the anode section exceeds a limiting value.

28. The method of claim 16, wherein the anode supply path includes a pressure-reducer which is connected to the fuel-source, and wherein the anode section is provided downstream of the pressure-reducer.

29. The method of claim 16, wherein the anode-side stack shut-off valve is closed again for the purpose of concluding the depressurizing before a closing pressure of the pressure-reducer is reached or when the closing pressure is reached.

30. A non-transitory computer-readable medium on which program instructions are stored which, when executed by a microprocessor, cause the microprocessor to execute the method of claim 16.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0036] The FIGURE shows a schematic view of a fuel-cell system according to at least one embodiment.

DETAILED DESCRIPTION OF THE DRAWING

[0037] Fuel—for example, hydrogen at up to 700 bar—is stored in the pressurized container H2. The pressurized container H2 provides hydrogen for the fuel-cell stack 300 which exhibits a plurality of fuel cells which are operated at a lower pressure level, for example 0.5 bar to 1 bar gauge pressure. A tank shut-off valve 211 is provided at one end of the pressurized container H2. Instead of just one pressurized container H2 with one tank shut-off valve 211, several pressurized containers H2 with one or more tank shut-off valves 211 might also have been provided. The fuel-conducting fluidic connection between the pressurized container H2 and the fuel-cell stack 300 supplies the anode A of the fuel-cell stack 300 with fuel and is designated as the anode supply path 210. In the system represented here, a pressure-reducer 244 is further provided. The pressure-reducer 244 lowers the storage pressure from up to 700 bar to a medium-pressure level of, for instance, 2 bar to 40 bar, or 12 bar to 18 bar. In the anode supply path 210 an anode-side stack shut-off valve 234 is further provided, which here acts as a further pressure-reducer and lowers the pressure from the medium-pressure level to the low pressure of the fuel cells. Here, the anode section MD is the section of the anode supply path 210 that is provided downstream of the pressure-reducer 244 and upstream of the anode-side stack cut-off valve 234. This anode section MD may also be designated as the medium-pressure region.

[0038] In order to prevent bursting of the pipelines or damage to components (screw couplings, sensors, anode shut-off valve, etc.) of the anode supply path 210 in the event of malfunction of the pressure-reducer 244, an excess-pressure valve 242 is provided here downstream of the pressure-reducer 244. Here, a water-separator 232, an anode-scavenging valve 238 and a recirculation pump 236 are provided in the recirculation flow path 216 of the anode subsystem downstream of the fuel-cell stack 300. The anode-scavenging pipe 239 here connects the anode-scavenging valve 238 to the cathode waste-gas pipe 416 which begins downstream of the cathode K of the fuel-cell stack and ends in the environment. A catalytic-converter surface (not shown) may have been provided in this waste-gas pipe 416. In a further embodiment, the anode-scavenging pipe 239 leads upstream of the cathode K into the cathode supply pipe 415, in particular downstream of the cathode-side stack shut-off valve 430. The directions of flow of the fuel and of the ambient air are represented here by arrows. The fuel-cell system has been integrated into a motor vehicle (not shown). The oxidant conveyor 410 compresses the oxidant O2 which is subsequently cooled in the heat-exchanger 420. Furthermore, a bypass pipe 460 is provided which branches off from the cathode supply pipe 415 and leads into the waste-gas pipe 416.

[0039] If fuel is now withdrawn, it expands and thereby cools down. If the fuel-cell system is now shut down, fuel that is cold relative to the installation-space temperature remains in the anode section MD. By reason of the large difference between the fuel temperature and the ambient temperature, heat is introduced into the fuel, as a result of which the fuel in the anode section MD warms up and the pressure in the anode section MD rises. Unless corrective measures are taken, the pressure might exceed the tripping pressure of the excess-pressure valve 242. Consequently, fuel would then be let out into the environment via the excess-pressure valve 242. According to the technology disclosed herein, this is prevented by the inactive control unit being reactivated, in order to initiate a pressure relief into the anode chamber of the fuel-cell stack 300 after the first period of time has elapsed. The pressure relief is achieved by a brief opening of the stack shut-off valve 234. After the pressure relief, the pressure in the anode section MD has fallen markedly. In particular, the anode-side stack shut-off valve 234 is opened here until such time as the pressure substantially corresponds to the closing pressure of the pressure-reducer. If the pressure in the anode section MD continues to rise due to the temperature, after a second period of time has elapsed a second pressure relief and, where appropriate, further pressure-relief operations can be initiated. Preferably, the control unit is inactive between the pressure-relief operations and the stack shut-off valve 234 is closed.

[0040] The foregoing description of the present invention serves only for illustrative purposes and not for the purpose of restricting the invention. Various amendments and modifications are possible within the scope of the invention without departing from the scope of the invention and its equivalents.