Method for releasing a fuel cell system and fuel cell system

Abstract

A method for enabling a fuel cell system includes the steps of: i) detecting a pressure value, which is indicative of the pressure within a section of the anode sub-system, wherein the section begins downstream of a pressure reducer; ii) relieving the pressure of the section during a pressure relief time interval, if the pressure value is greater than a pressure limit value and a release request is present; and then iii) enabling the fuel cell system if the pressure value in the section after the pressure relief is less than the pressure limit value.

Claims

1. A method for enabling a fuel cell system, comprising: detecting a pressure value which is indicative of pressure within a section of an anode subsystem, the section beginning downstream of a pressure reducer the pressure value being detected during an inactive phase of the fuel cell system; relieving pressure of the section if the pressure value is greater than a pressure limit value and there is an enabling request; and subsequently enabling the fuel cell system if the pressure value in the section after the pressure relieving is smaller than the pressure limit value, the enabling comprising transferring the fuel cell system from the inactive phase into an active operating state.

2. The method according to claim 1, wherein the pressure relieving takes place by having fuel flow out of the section directly or indirectly into an anode of a fuel cell stack of the fuel cell system.

3. The method according to claim 1, wherein the pressure relieving take place by having fuel flow out of the section directly or indirectly into an exhaust gas system of the fuel cell system.

4. The method according to claim 1, wherein a test is carried out before the pressure relieving and after the enabling request as to whether any possible tank shut-off valves are closed upstream of the pressure reducer, and the pressure relieving from the section takes place only if the possible tank shut-off valves are closed.

5. The method according to claim 1, wherein fuel which is discharged during the pressure relieving is converted catalytically on a catalytic converter surface.

6. The method according to claim 2, wherein the fuel which is discharged during the pressure relieving is converted catalytically on a catalytic converter surface.

7. The method according to claim 3, wherein the fuel which is discharged during the pressure relieving is converted catalytically on a catalytic converter surface.

8. The method according to claim 1, wherein the fuel cell system operates an oxidizing agent conveyor such that fuel is diluted before the fuel leaves the fuel cell system.

9. The method according to claim 2, wherein the fuel cell system operates an oxidizing agent conveyor such that the fuel is diluted before the fuel leaves the fuel cell system.

10. The method according to claim 3, wherein the fuel cell system operates an oxidizing agent conveyor such that the fuel is diluted before the fuel leaves the fuel cell system.

11. The method according to claim 1, wherein the fuel cell system is enabled if the pressure value in the section after the pressure relieving is smaller than a maximum operating pressure limit value which may occur during an energy providing operation of the fuel cell system.

12. The method according to claim 1, wherein a pressure relieving operation is not carried out, and the enabling already takes place after detecting the pressure value if the detected pressure value is smaller than the pressure limit value.

13. A fuel cell system, comprising: at least one control unit, wherein the control unit is operatively configured to: detect a pressure value which is indicative of pressure within a section of an anode subsystem, the section beginning downstream of a pressure reducer, the pressure value being detected during an inactive phase of the fuel cell system; subsequently, relieve the pressure of the section if the pressure value is greater than a pressure limit value and there is an enabling request; and subsequently, transfer the fuel cell system from the inactive phase into an active operating state if the pressure value in the section downstream of the pressure relieving is smaller than the pressure limit value.

14. A motor vehicle, comprising a fuel cell system according to claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of a fuel cell system.

(2) FIG. 2 is a highly schematic graph showing the temporal evolvement of the pressure value p.sub.MD.

(3) FIG. 3 is a flow chart showing one refinement of the method steps disclosed herein.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 diagrammatically shows the fuel cell system disclosed herein. Fuel, for example hydrogen at 700 bar, is stored in the pressure vessel 200. The pressure vessel 200 provides hydrogen for a fuel cell stack 300 with a multiplicity of fuel cells which are operated at a lower pressure level, for example from 0.5 to 1 bar(g) (=positive pressure with respect to atmospheric pressure). A tank shut-off valve 210 is provided at one end of the pressure vessel 200. Instead of merely one pressure vessel 200 with one tank shut-off valve 210, a plurality of pressure vessels 200 with a plurality of tank shut-off valves 210 might likewise be provided. In the system which is shown here, furthermore, two pressure stages are provided which operate in each case by way of a pressure reducer 222, 224. The first pressure stage lowers the pressure from 700 bar to a medium pressure level of, for example, from 10 to 20 bar or from 13 to 16 bar (medium pressure range). The second pressure stage lowers the pressure from the medium pressure level to the low pressure of the fuel cells. The region downstream of the first pressure reducer 224 is the section MD disclosed herein. The latter is divided further here into a medium pressure region MD and a low pressure region ND. Here, a mechanical proportional pressure regulator is used as first pressure reducer 224. Various technologies for the second pressure regulator 222 can be used in the second pressure stage, for example injectors, Venturi nozzles and mechanical pressure regulators. In order to prevent bursting of the pipelines in the case of a malfunction in the pressure reducers 222, 224, in each case one pressure relief valve 242, 244 is provided here downstream of the first and the second pressure reducer 222, 224. Here, a water separator 232, an anode flush valve 238, a recirculation pump 236 and a Venturi nozzle 234 are provided in the recirculation circuit in the anode subsystem downstream of the fuel cell stack 300. Here, the anode flush line 239 connects the anode flush valve 238 to the cathode exhaust gas line 416 which begins downstream of the cathode K of the fuel cell stack 300 and ends in the surroundings. A catalytic converter surface (not shown) can be provided in said exhaust gas line 416.

(5) In a further refinement, the anode flush line 239 opens upstream of the cathode into the cathode feed line 415, in particular downstream of the cathode-side stack shut-off valve 430. It can advantageously be provided that the catalytic conversion of the fuel takes place during the pressure relieving in the section MD on the surface of the cathode K of the fuel cell stack 300. To this end, other pipe connections of the anode and the cathode are also conceivable. The oxidizing agent conveyor 410 can be set up to dilute fuel which is discharged during the pressure relieving with ambient air. This can take place by way of the cathode or preferably by way of a cathode bypass 460. The cathode-side stack shut-off valves 430, 440 might then remain closed during the pressure relieving. The flow direction of the fuel and the ambient air are shown here by way of arrows. The fuel cell system is installed into a motor vehicle (not shown).

(6) FIG. 2 very diagrammatically shows the temporal evolvement of the pressure value p.sub.MD. Here, the pressure in the section MD serves as the pressure value. The fuel cell system was parked here at a time t0. On account of pronounced heating of the fuel cell system during the inactive phase, the pressure rises continuously. At the time t1, the pressure in the section MD reaches the limit pressure or pressure limit value p.sub.TAVc. From this time, the tank shut-off valve 210 is shut off for all further functions for safety reasons. It can be opened again only when an enabling operation has taken place. The pressure in the section MD rises further until, at the time t2, the triggering pressure p.sub.PRVo of the pressure relief valve which is provided in the section MD is reached. The pressure relief valve opens, and the pressure in the section MD decreases until the pressure has dropped at the time t3 to the closing pressure p.sub.PRVc of the pressure relief valve. After the closure, the pressure in the section MD here increases on account of the continuing heating once again to the triggering pressure P.sub.PRVo (time t4), and subsequently decreases again to the closing pressure p.sub.PRVc (time t5). Here, the pressure does not decrease to a pressure below the limit pressure of the tank shut-off valve. As a consequence, the tank shut-off valve will therefore always be shut off in the case of a starting procedure if the technology disclosed herein is not used. At the time t6, an enabling request is then issued, for example because a user wishes to start the motor vehicle. At this time, the method steps according to FIG. 3 are initiated.

(7) FIG. 3 diagrammatically shows one refinement of the method steps disclosed herein. The method disclosed herein begins with the step S100. In the step S200, the pressure value p.sub.MD in the section can be detected.

(8) In the step S300, it can be determined whether the detected pressure value p.sub.MD (here, therefore the pressure in the section MD) is greater than the triggering pressure p.sub.PRVo of the pressure reducer 224. If this is the case, the fuel cell system or the tank shut-off valve 210 is or remains shut off, and a corresponding warning message is output to the user and/or to third parties (for example, a control center, for example via telemetry) (cf. step 730). This does not have to be implemented in this way, however.

(9) If the detected pressure value p.sub.MD is in the meantime not greater than the triggering pressure p.sub.PRVo, it can be determined in step S400 whether the detected pressure value p.sub.MD is greater than the pressure limit value p.sub.TAVc of the tank shut-off valve 210. If this is not the case, the enabling operation can take place (cf. step S710). If the detected pressure value p.sub.MD is in the meantime greater than the pressure limit value p.sub.TAVc, the pressure has not dropped by way of the pressure relieving during the inactive phase of the fuel cell system as desired. Here, it has even risen noticeably (cf. FIG. 2). In this case (that is to say, p.sub.TAVc<p.sub.MD<p.sub.PRVo), a check is first of all made here in step S510 as to whether the tank shut-off valve 210 is closed. If this is the case, the section MD is relieved of pressure in the step S520, here during the pressure relief time interval t.sub.DE (cf. FIG. 2). This can take place, for example, by virtue of the fact that the anode flush valve 238 is opened. At this time, the fuel cell system preferably does not provide any electric power to other electric consumers. Via the anode flush valve 238, the fuel passes into the cathode exhaust gas line 416, in which the fuel is diluted with ambient air (cf. FIG. 1). Other apparatuses for relieving the pressure are also conceivable, however. For example, a bypass line can branch off from the section MD and can open in the cathode exhaust gas line 416. During the pressure relieving, operations are carried out which bring about a reduction of the pressure value p.sub.MD in the section MD, if there is no malfunction. If, however, there is a malfunction which was also responsible, for example, for the pressure rise in the inactive phase, for example a defective pressure reducer 224, the pressure value also continues to rise in the pressure relief time interval t.sub.DE (cf. dotted line in FIG. 2). In the step S600, it is determined whether the detected pressure value p.sub.MD at the time t6 after the pressure relieving (here, after the pressure relief time interval t.sub.DE) is smaller than the pressure limit value p.sub.TAVc. If this is the case, the enabling operation can take place (cf. step S710). In this case, the pressure rise during the inactive phase of the fuel cell system is to be attributed to environmental influences and/or insignificant leaks which are not critical for the operation of the fuel cell system. A signal can nevertheless optionally be output. If the detected pressure value p.sub.MD is in the meantime greater than the pressure limit value p.sub.TAVc, there is probably a malfunction. The fuel cell system or the tank shut-off valve 210 is then shut off or remains shut off in the step 720, and a corresponding warning signal is output to the user and/or to third parties (for example, a control center, for example via telemetry) (cf. step 720).

(10) The preceding description of the present invention serves merely for illustrative purposes and not for the purpose of restricting the invention. Within the context of the invention, various amendments and modifications are possible, without departing from the scope of the invention and its equivalents.

LIST OF DESIGNATIONS

(11) Fuel cell stack 300 Anode space A Pressure vessel 200 Tank shut-off valve 210 Anode inflow path 215 Recirculation flow path 216 Second pressure reducer 222 First pressure reducer 224 Water separator 232 Anode flush valve 238 Recirculation jet pump 234 Recirculation conveyor 236 Anode flush line 239 Section MD Low pressure section ND Cathode space K Oxidizing agent conveyor 410 Cathode inflow path 415 Heat exchanger 420 Feed line/stack shut-off valve 430 Exhaust gas/stack shut-off valve 440 Cathode exhaust gas path 416 Fuel cell bypass 460