AU2017227948A1

AU2017227948A1 - Fuel cell system with leakage detection

Info

Publication number: AU2017227948A1
Application number: AU2017227948A
Authority: AU
Inventors: Torsten Brandt; Michael Braunecker; Joachim Hoffmann; Torsten Lochner; Arno Mattejat; Walter STÜHLER
Original assignee: Siemens AG
Current assignee: Siemens Energy Global GmbH and Co KG
Priority date: 2016-02-29
Filing date: 2017-02-27
Publication date: 2018-09-20
Anticipated expiration: 2037-02-27
Also published as: KR102124437B1; WO2017148869A1; EP3211700B1; EP3211700A1; TR201810081T4; ES2683240T3; KR20180114949A; AU2017227948B2

Abstract

The invention relates to a fuel cell system with multiple fuel-cell modules (1, 2, 3) which are operated with the reactants hydrogen and oxygen and each of which has an inlet (4, 6) and an outlet (5, 7) for each of the two reactants, wherein the modules are connected in parallel into two separate circuits (8, 9) of the two reactants via the inlets and outlets, said reactants being introducible into the respective circuit via a supply valve (10, 12) and being dischargeable via a disposal valve (11, 13). The fuel cell modules (1, 2, 3) are connected to the reactant circuits (8, 9) at the inlets (4, 6) and the outlets (5, 7) of the fuel cells via controllable opening/closing valves (18, 19, 21, 22), and sensors (22) are connected to the outlets (5) for at least one of the two reactants in order to detect the respective other reactant. Upon detecting a content of the respective other reactant exceeding a specified threshold, the sensors generate signals (25) in order to separate the fuel cell modules (1, 2, 3) with the outlets (5) where the exceeded threshold was detected from the two reactant circuits (8, 9) via the opening/closing valves (18, 19, 21, 22).

Description

(57) Zusammenfassung:

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Veroffentlicht:

— mit internationalem Recherchenbericht (Artikel 21 Absatz 3)

Brennstoffzellenanlage mit mehreren Brennstoffzellenmodulen (1, 2, 3), die mit den Reaktanden Wasserstoff und Sauerstoff betrieben werden und fur jeden der beiden Reaktanden jeweils einen Einlass (4, 6) und einen Auslass (5, 7) aufweisen, iiber die sie parallel in zwei separate Kreislaufe (8, 9) der beiden Reaktanden geschaltet sind, in die jeweils der betreffende Reaktand iiber ein Versorgungsventil (10, 12) einleitbar und tiber ein Entsorgungsventil (11, 13) ausleitbar ist, wobei die Brennstoffzellenmodule (1, 2, 3) an ihren Einlassen (4, 6) und Auslassen (5, 7) tiber steuerbare Auf-/Zu-Ventile (18, 19, 21, 22) an den ReaktandenKreislaufen (8, 9) angeschlossen sind und an den Auslassen (5) fur zumindest einen der beiden Reaktanden Sensoren (22) zur Detektion des jeweils anderen Reaktanden angeschlossen sind, die bei Detektion eines einen vorgegebenen Schwellenwert tiberschreitenden Gehalts des jeweils anderen Reaktanden Signale (25) erzeugen, um iiber die Auf-/Zu-Ventile (18, 19, 21, 2) die Brennstoffzellenmodule (1, 2, 3), an deren Auslassen (5) die Schwellenwertuberschreitung detektiert wurde, von den beiden Reaktanden-Kreislaufen (8, 9) zu trennen.

PCT/EP2017/054522 / 2016P04092WO

Description

Fuel cell system with leakage detection

The invention relates to a fuel cell system with a number of fuel cell modules, which are operated with the reactants hydrogen and oxygen. The fuel cell modules may consist of individual or multiple fuel cells (fuel cell stack).

A fuel cell stack consisting of a number of fuel cells is known from WO2015024785 (Al), which has a hydrogen inlet and outlet and also an oxygen inlet and outlet. The fuel cell stack is connected to a hydrogen circuit via its hydrogen inlet and outlet, into which hydrogen circuit hydrogen can be introduced via a supply valve and discharged via a discharge valve. Furthermore, the fuel cell stack is connected to an oxygen circuit at its oxygen inlet and outlet, into which oxygen circuit oxygen can be introduced via a further supply valve and discharged via a further discharge valve. The hydrogen circuit and the oxygen circuit each contain a circulation pump with an assigned pump controller, in order to control or regulate the oxygen-side and the hydrogen-side circulation operations independently from one another. In particular, the circulation operations can be applied to a plurality of fuel cells of the fuel cell stack supplied in parallel.

A fuel cell system constructed in a cascaded manner with a plurality of fuel cells and/or groups of fuel cells is known from DE102007040836 (Al), wherein each of the fuel cells has a first gas compartment for a first process gas with a first reactant, in particular hydrogen, and a second gas compartment for a second process gas with a second reactant, in particular

PCT/EP2017/054522 / 2016P04092WO oxygen, between which an ion-permeable electrolyte, in particular a polymer electrolyte membrane (PEM), is arranged. If leak forms in the membrane, this leads to a gas exchange and thus to a direct thermal conversion of the reactants hydrogen and oxygen. In order to prevent a fuel cell from consequential damage in the event of a leak in its membrane, and to keep the hydrogen-oxygen gas mixture away from the downstream fuel cells or fuel cell groups, and thus to also protect these, oxygen sensors are arranged in the line connections between the fuel cells or fuel cell groups, i.e. at their hydrogen outlets, in each case. When a predetermined limit value for the oxygen content is exceeded, the hydrogen and oxygen supply into the first fuel cell group and thus for the entire fuel cell system is interrupted.

As an alternative to oxygen detection, the hydrogen-oxygen gas mixture can be catalytically converted. In doing so, on the one hand the gas mixture is destroyed, which safeguards the downstream cells from thermal damage particularly safely; on the other, the gas mixture can be detected by temperature measurement due to the resulting heat of reaction. If operation of the fuel cell system continues, it remains a problem, however, that the faulty fuel cell in the region of the leak no longer functions from an electrochemical perspective and the fuel cell voltage drops.

A PEM fuel cell operating with hydrogen and oxygen is known from JPH06223850 (A), in which a hydrogen detector is arranged in the oxygen outlet. In the event of detection, the hydrogen detector generates a signal, with which the hydrogen supply for the fuel cell is halted via a controllable on/off valve.

A fuel cell operating with hydrogen and oxygen is known from

PCT/EP2017/054522 / 2016P04092WO

JP4923426 (B), in which the hydrogen is conducted in a circuit. A control unit obtains measurement values of the electrical voltage, temperature, input pressures as well as the hydrogen concentration in the oxygen outlet of the fuel cell and controls the pressure difference between the anode side and cathode side via the valves, so that the hydrogen concentration in the oxygen outlet remains below a first threshold value. If a second threshold value is reached, then an alarm is generated. Finally, if a third threshold value is reached, the fuel cell is switched off.

US2004018404 (Al) discloses a fuel cell operating with hydrogen and air. A control unit obtains as measurement values the pressure of the supplied hydrogen, the pressure and flow rate of the supplied air, the generated current as well as the hydrogen concentration in the air outlet measured by a hydrogen sensor and controls a current controller and the hydrogen and air supply. As a function of the operating status of the fuel cell, a certain tolerance range for the hydrogen concentration is provided in the oxygen outlet, within which the pressure difference, flow rate and current are regulated.

The object underlying the invention is to specify a fuel cell system operated with hydrogen and oxygen with a plurality of fuel cells and/or groups of fuel cells, which can continue to be operated safely even in the event of a leak.

In accordance with the invention, the object is achieved by the fuel cell system defined in claim 1, of which advantageous developments are specified in the subclaims.

The subject matter of the invention is thus a fuel cell system with a number of fuel cell modules, which are operated with

PCT/EP2017/054522 / 2016P04092WO the reactants hydrogen and oxygen and have an inlet and an outlet for each of the two reactants respectively, by way of which they are switched in parallel in two separate circuits of the two reactants, into which the appropriate reactant can be introduced by way of a supply valve and can be discharged by way of a discharge valve in each case, wherein the fuel cell modules are connected at their inlets and outlets via controllable on/off valves to the reactant circuits and sensors for detecting the respective other reactants are connected to the outlets for at least one of the two reactants, said sensors generating signals when a concentration of the respective other reactant, which exceeds a predetermined threshold value, is detected, in order to separate the fuel cell modules, at the outlets of which the exceeding of the threshold value was detected, from the two reactant circuits by way of the on/off valves.

Thus, as soon as a leak is detected in one of the fuel cell modules, said module is separated from the supply with the reactants on both the inlet and outlet side, so that a spreading of the foreign reactant penetrating through the leak into the other fuel cell module is excluded. In addition to halting the chemical fuel cell process, the appropriate fuel cell module must also be electrically separated from the remaining modules, provided this is not already operationally uncoupled via diodes. The intact fuel cell modules continue to be supplied by the reactant circuits, wherein optionally only an output adjustment is required. This does not take place for each individual fuel cell module, however, but rather via the overall regulation of the reactant circuits.

The leak monitoring can fundamentally take place on both sides

PCT/EP2017/054522 / 2016P04092WO of the fuel cell module, i.e. for both reactants. Preferably, however, the sensors are only connected to the outlets for one of the two reactants, the pressure of which is then set by corresponding pressure regulation to be slightly lower in the reactant circuits than that of the other reactant.

Since the viscosity of oxygen is greater than that of hydrogen and therefore more hydrogen flows through the leak than oxygen in the event of a fault, the pressure in the oxygen circuit is preferably set to be higher than in the hydrogen circuit and the hydrogen outlet of the fuel cell module is monitored for the presence of oxygen.

The sensors used for leak monitoring are advantageously arranged between the outlets of the fuel cell module and the on/off valves, via which the outlets are connected to the respective reactant circuits. This makes it possible to achieve that in the event of detection the appropriate fuel cell module can be separated from the reactant circuit, before the foreign reactant reaches it. This is particularly advantageous if the detection is effected with a delay, for example in the case of detection for catalytic combustion of the hydrogen and detection of the heat development, or the fuel cell module is initially separated from the reactant circuits on the inlet side, and only from the outlet side with a delay, so that the fuel cell module which is then switched off is depressurized. By providing a sufficiently large gas volume between the site of the detection with the sensor and the site of the separation with the on/off valve, virtually any switch-off delay is possible without endangering the other fuel cell module.

The sensors can be embodied to detect the respective other

PCT/EP2017/054522 / 2016P04092WO reactant without destruction. This includes, in addition to optically operating sensors, which measure the concentration of the reactant to be measured on the basis of its wavelengthspecific absorption, in particular also thermal conductivity detectors, in which the measurement effort is low and which are particularly suitable for measuring two-component gas mixtures .

Since, in the event of a leak, the appropriate fuel cell module is only switched off when the gas concentration of the detected foreign reactant exceeds a predetermined threshold value, it is possible for even only a small amount of the foreign reactant to reach the respective circuit to be protected and possibly to grow there over a long time, wherein it is no longer readily detectable specifically for the faulty fuel cell module. In order to avoid this problem, in accordance with an advantageous development of the fuel cell system according to the invention, a device for catalytically combusting the hydrogen is arranged in the circuit of the reactant monitored by the sensors in a section downstream of the last outlet and upstream of the first inlet of a fuel cell module. Alternatively, the sensors themselves can be embodied to catalytically combust the hydrogen, wherein the presence of the foreign reactant is detected by measuring the temperature increase as a result of the combustion heat.

As already explained above, when a faulty fuel cell module is switched off, the intact fuel cell modules continue to be supplied by the reactant circuits, wherein an output adjustment may be required, which does not take place for each individual fuel cell module, however, but rather via the overall regulation of the reactant circuits. For this purpose, the reactant circuits each contain a circulation pump with an

PCT/EP2017/054522 / 2016P04092WO assigned pump controller, the pump controllers are embodied to control the output of the appropriate circulation pumps as a function of an item of information relating to the number of fuel cell modules connected to the reactant circuits, wherein this information is updated as a function of the signals generated by the sensors.

To further explain the invention, reference is made below to the figures in the drawing; each show in detail in a schematic representation :

FIG 1 a first exemplary embodiment of the fuel cell system according to the invention and

FIG 2 a second exemplary embodiment of the fuel cell system according to the invention.

The same reference characters have the same meaning in the various figures.

Fig. 1 shows a fuel cell system with a number of fuel cell modules 1, 2, 3, which are operated with the reactants hydrogen H2 and oxygen O2. As shown in the example of the fuel cell module 1, all fuel cell modules 1, 2, 3 have an inlet 4 and an outlet 5 for the reactant hydrogen and an inlet 6 and an outlet 7 for the reactant oxygen. The fuel cell modules 1, 2, 3 are connected in parallel to a hydrogen circuit 8 via the inlet 4 and the outlet 5 and connected in parallel to an oxygen circuit 9 via the inlet 6 and the outlet 7. The hydrogen can be introduced into the circuit 8 via a controllable supply valve 10 and discharged from the circuit 8 via a discharge valve 11. Accordingly, the oxygen can be introduced into the circuit 9 via a controllable supply valve

PCT/EP2017/054522 / 2016P04092WO and discharged therefrom via a discharge valve 13. Each reactant circuit 8, 9 contains a controllable circulation pump (compressor) 14, 15 for conducting the appropriate reactant through the fuel cell modules 1, 2, 3 connected in parallel. Pump controllers 16, 17 assigned to the pumps 14, 15 are used to set the flow rate and pressure in the reactant circuits 8,

9. In all other respects, reference is made to WO2015024785 (Al) mentioned in the introduction with regard to the circulation operations, from which the supply of a fuel cell stack with reactants from two separate gas circuits is known.

As shown in turn in the example of the fuel cell module 1, each of the fuel cell modules 1, 2, 3 is connected at its inlets 4, 6 and outlets 5, 7 via controllable on/off valves 18, 19, 20, 21 to the respective reactant circuits 8, 9. In the example shown in Fig. 1, in each of the fuel cell modules 1, 2, 3, connected at the outlet 5 for the reactant hydrogen there is a sensor 22 for detecting the presence of the respective other reactant, here oxygen. The sensor 22 itself or an evaluation device 23 downstream therefrom, which can be attributed to the sensor and which can also be part of an upstream controller 24 for the fuel cell system, as in the case of the pump controllers 16, 17, generates a signal 25 when an oxygen concentration which exceeds a predetermined threshold value is detected, in order to separate the fuel cell module, e.g. 1, at the outlet 5 of which the exceeding of the threshold value was detected, from the two reactant circuits 8, 9 by way of the on/off valves 18, 19, 20, 21. The signal 25 can also be used to electrically separate the faulty fuel cell module 1 from the remaining modules 2, 3 or the electrical load via switches not shown here.

By virtue of a sufficiently high gas volume 26 being provided

PCT/EP2017/054522 / 2016P04092WO for the line section between the sensor 22 and the downstream on/off valve 19, it is ensured that the foreign reactant, in this case oxygen, does not reach the hydrogen circuit 8 even if the separation takes place with a delay. Nevertheless, should small amounts of oxygen reach the hydrogen circuit 8, they are destroyed in a device 27 for catalytically combusting the hydrogen. This device 27 is arranged in a section of the hydrogen circuit 8 which, when viewed in the direction of circulation, lies downstream of the outlet 5 of the last fuel cell module 3 and upstream of the inlet 4 of the first fuel cell module 3.

The pump controllers 16, 17 contain, in a memory not shown here, information on the number of fuel cell modules 1, 2, 3 connected to the reactant circuits 8, 9, in order to control the pump output as a function thereof. When generating the signal 25 for closing the on/off valves 18, 19, 20, 21, this information is updated in the memory, so that the pump output is adjusted to the amended relationships. The same also applies for supplying the fuel cell modules 1, 2, 3 with coolant, not shown here, wherein the cooling output is adjusted.

The exemplary embodiment of the fuel cell system according to the invention shown in Fig. 2 differs from that in Fig. 1 in that the oxygen outlets 7 are also monitored by means of further sensors 28 for the presence of the other reactants, here hydrogen. If one of the sensors 22, 28 ascertains that the respectively detected foreign reactant has exceeded a threshold value, the evaluation device 23 generates the signal 25 for separating the appropriate fuel cell module, e.g. 1, from the reactant circuits 8, 9. Provided that the sensors 22, 28 possess their own evaluation devices for detecting the

PCT/EP2017/054522 / 2016P04092WO exceedance of a threshold value, each sensor 22, 28 can itself generate the signal 25.

In the exemplary embodiment shown, a device 29 for catalytically combusting hydrogen is also provided in the oxygen circuit 9. Alternatively, the sensors 22, 28 themselves can be embodied to catalytically combust the hydrogen and to detect the heat development arising thereby.

PCT/EP2017/054522 / 2016P04092WO

Claims

Claims

1. A fuel cell system with a number of fuel cell modules (1,
2, 3), which are operated with the reactants hydrogen and oxygen and have an inlet (4, 6) and an outlet (5, 7) for each of the two reactants respectively, by way of which they are switched in parallel in two separate circuits (8, 9) of the two reactants, into which the appropriate reactant can be introduced by way of a supply valve (10, 12) and can be discharged by way of a discharge valve (11, 13) in each case, wherein the fuel cell modules (1, 2, 3) are connected at their inlets (4, 6) and outlets (5, 7) via controllable on/off valves (18, 19, 21, 22) to the reactant circuits (8, 9) and sensors (22, 28) for detecting the respective other reactants are connected to the outlets (5, 7) for at least one of the two reactants, said sensors generating signals (25) when a concentration of the respective other reactant, which exceeds a predetermined threshold value, is detected, in order to separate the fuel cell modules (1, 2, 3), at the outlets (5,

7) of which the exceeding of the threshold value was detected, from the two reactant circuits (8, 9) by way of the on/off valves (18, 19, 21, 2).

2. The fuel cell system as claimed in claim 1, characterized in that the sensors (22) are only connected to the outlets (5) for one of the two reactants, and the pressure in the circuit (8) of this one reactant is lower than the pressure in the circuit (9) of the other reactant.
3. The fuel cell system as claimed in claim 2, characterized in that the one reactant is hydrogen and the other reactant is oxygen .

PCT/EP2017/054522 / 2016P04092WO
4. The fuel cell system as claimed in one of the preceding claims, characterized in that the sensors (22, 28) are arranged between the outlets (5, 7) and the on/off valves (19, 21) connecting these to the respective reactant circuits (8,

9) .
5. The fuel cell system as claimed in claim 4, characterized in that a gas volume (26) of a predetermined size is provided between the sensors (22) and the on/off valves (19), which connect the outlets (5) monitored by the sensors (22) to the reactant circuit (8).
6. The fuel cell system as claimed in one of the preceding claims, characterized in that the sensors (22) are embodied to detect the respective other reactant without destruction.
7. The fuel cell system as claimed in claim 6, characterized in that a device (27, 29) for catalytically combusting the hydrogen is arranged in the circuit (8, 9) of the reactant monitored by the sensors (22, 28) in a section downstream of the last outlet (5, 7) and upstream of the first inlet (6, 4) of a fuel cell module (3 or 1).
8. The fuel cell system as claimed in one of claims 1 to 5, characterized in that the sensors (22, 28) are embodied to catalytically combust the hydrogen and to detect the heat development.
9. The fuel cell system as claimed in one of the preceding claims, characterized in that the reactant circuits (8, 9) each contain a circulation pump (14, 15) with an assigned pump controller (16, 17), the pump controllers (16, 17) are

PCT/EP2017/054522 / 2016P04092WO embodied to control the output of the circulation pumps (14, 15) as a function of an item of information relating to the number of fuel cell modules (1, 2, 3) currently connected to the reactant circuits (8, 9) and this information is updated as a function of the signals (25) generated by the sensors (22, 28) .

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Fig. 1

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Fig. 2

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