Leak detection on a high-temperature fuel cell or electrolyzer

Abstract

An electrochemical system includes an electrochemical device having a stack of elementary electrochemical cells each including an electrolyte interposed between a cathode and an anode; ducts for supplying the anodes and the cathodes with gas and for collecting the gases generated by the latter; an enclosure having the electrochemical device housed therein and including at least one inlet duct and one outlet duct to circulate an air flow in the enclosure; and a circuit for analyzing the air in the enclosure. The circuit includes a sensor capable of measuring an oxygen content present in the outlet duct of the enclosure; and an analysis unit capable of diagnosing a leak of the device when the measured oxygen content differs from a predetermined oxygen content in the inlet duct of the enclosure.

Claims

1. An electrochemical system comprising: an electrochemical device forming a high-temperature steam electrolyzer or high-temperature fuel cell, the device comprising: a stack of elementary electrochemical cells each comprising an electrolyte interposed between a cathode and an anode; ducts for supplying the anodes and the cathodes with gas and for collecting the gases generated by said anodes and cathodes; an enclosure having the electrochemical device housed therein and comprising at least one inlet duct and one outlet duct to circulate an air flow in the enclosure; and a circuit for analyzing the air in the enclosure; wherein the circuit for analyzing the air in the enclosure comprises: a sensor that measures an oxygen content present in the at least one outlet duct of the enclosure; and an analysis unit that diagnoses a leak of the electrochemical device when the measured oxygen content differs from a predetermined oxygen content in the at least one inlet duct of the enclosure; wherein the analysis unit comprises a computer-readable medium comprising instructions, which when executed by the analysis unit, cause the analysis unit to determine a leak flow rate at the level of the electrolyzer cathodes according to the following relation:
D.sub.f.sub.H2=2.Math.(.sub.0.sub.1).Math.D.sub.Air in which expression D.sub.f.sub.H2 is said leak flow rate, D.sub.Air is the air flow in the enclosure, .sub.0 is the predetermined oxygen content in the at least one inlet duct of the enclosure, and .sub.1 is the measured oxygen content in the at least one outlet duct of the enclosure.

2. The electrochemical system of claim 1, wherein the analysis circuit comprises a pumping unit capable of pumping air from the at least one outlet duct and of generating an air flow having a predetermined maximum volume flow rate, and wherein the oxygen sensor measures the oxygen content downstream of the pumping unit.

3. The electrochemical system of claim 1, wherein the analysis circuit comprises a drying unit for drying air present in at least one the outlet duct of the enclosure, and wherein the oxygen sensor measures the oxygen content in the air dried by the drying unit.

4. The electrochemical system of claim 1, wherein the electrochemical device is a high-temperature electrolyzer, and wherein the analysis unit diagnoses a leak at the level of the electrolyzer cathodes when the measured oxygen content in the at least one outlet duct of the enclosure is inferior to the predetermined oxygen content in the at least one inlet duct of the enclosure, and/or diagnoses a leak at the level of the anodes of the device when the measured oxygen content in the at least one outlet duct of the enclosure is superior to the predetermined oxygen content in the at least one inlet duct of the enclosure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be better understood on reading of the following description provided as an example only in relation with the accompanying drawings, where the same reference numerals designate the same or similar elements, among which:

(2) FIG. 1 is a simplified view of an elementary electrochemical cell of an HTSE electrolyzer;

(3) FIG. 2 is a simplified view of a stack of cells according to FIG. 1;

(4) FIG. 3 is a simplified view of an electrochemical cell of a SOFC, and

(5) FIG. 4 is a simplified view of an electrochemical system according to the invention including a hot area, the gas inlet and outlet circuits, and the measuring chain incorporating an oxygen detector.

DETAILED DESCRIPTION OF THE INVENTION

(6) In the following, terms upstream and downstream designate locations in ducts and bypasses according to the gas circulation therein.

(7) Referring to FIG. 4, the system according to the invention comprises: an HTSE electrolyzer 20, for example, that described in relation with FIGS. 1 and 2 and comprising an assembly of ducts 52, 54, 56, 58 for the supply and the collection of the gases of the anodes and of the cathodes of the electrochemical cells of the electrolyzer an enclosure 60 having electrolyzer 20 housed therein, ducts 52, 54, 56, 58 crossing a wall of enclosure 60 for their connection to gas supply and collection circuits (not shown). Enclosure 60 also comprises an air inlet duct 62 and an air outlet duct 64, enclosure 60 for example being gas- and liquid-tight everywhere else. Duct 62 is capable of being connected to an air supply circuit (not shown) to apply an sweeping with air of the hot area surrounding electrolyzer 20, the sweeping air being discharged through outlet duct 64; and an air analysis device 66 connected to outlet duct 64 of enclosure 60.

(8) Analysis device 66 comprises: a bypass loop 68 of the outlet duct 64 enabling to sample gas from outlet duct 64 and to inject back the gas sampled therefrom downstream of the sampling; a drying unit, particularly, a droplet separator 70, to remove water present in the gas flowing through bypass 68; a pumping unit 72, arranged downstream of droplet separator 70, to sample, therethrough, gas from outlet duct 64; an oxygen sensor 74, arranged downstream of pumping unit 70 and measuring the oxygen content delivered by the latter, and accordingly the oxygen content of the gas .sub.1 present in outlet duct 64; and an analysis unit 76 connected to the oxygen sensor to receive the measured content .sub.1 and implement a processing of this content to detect a leak of electrolyzer 20.

(9) For example, the sweeping air injected into the enclosure is air sampled outside, and accordingly having at the atmospheric pressure an oxygen content close to 20.95% and oxygen sensor 74 has a measurement range from 0% to 25% of O.sub.2, for example, an oxymeter such as used for oxygen deficiency monitoring. The sensor is for example a Drger detection system, that is, the Polytron 7000 Transmitter with a O2 LS sensor (3-electrode temperature-compensated electrochemical sensor).

(10) The sweeping air flow D.sub.Air (l/min) introduced into enclosure 60 through inlet duct 62 ensures a renewal of N times per minute of the air contained in enclosure 60. Flow rate D.sub.Air is thus equal to:
D.sub.Air=N.Math.V.sub.enclosure
where V.sub.enclosure is the volume (in l) of enclosure 60.

(11) According to the volume of enclosure 60 and to the selected number N of renewals, essentially dictated by security considerations, the sweeping air flow rate D.sub.Air may be too high for a direct analysis, for example, if the speed in the gas lines exceeds the maximum value recommended by the manufacturer of the oxygen sensor.

(12) According to an embodiment taking into account the previous constraint, but also to guarantee that a gas flow always flows on the oxygen detector, pumping unit 72 is installed in series with the sensor in bypass 68. Pumping unit 72 is thus selected to generate a gas flow rate appropriate for the operation of sensor 74

(13) Further, when a leak on the stack appears on the cathode side, a certain leak flow rate of gas mixture H.sub.2+H.sub.2O enters into enclosure 60. There thus is an increase in the quantity of water vapor in the sweeping air, on the one hand directly originating from the cathode mixture, and on the other hand after the combustion of hydrogen with the oxygen of the sweeping air. Since the temperature in outlet duct 64 is lower than that in enclosure 60, or even equal to the room temperature, the water vapor risks condensing on the wall of duct 64 and bypass duct 68. According to an embodiment enabling to protect oxygen sensor 74 from possible water drops, and thus to respect the recommendations of the manufacturer regarding the maximum humidity content of the analyzed air, droplet separator 70 is installed in series with and upstream of the oxygen sensor in bypass 68.

(14) According to the previous example, corresponding to a leak on the cathode side, the combustion of hydrogen with the oxygen of the sweeping air will cause a decrease in the oxygen content in the air analyzed by sensor 74. The latter being calibrated in the range corresponding to the atmospheric air, it may provide a measurement within a typical range from 0% to 25% of oxygen in the analyzed air. The standard oxygen content being .sub.0=20.95% and thus corresponding to the oxygen content introduced into enclosure 60, a measurement .sub.1 of a value smaller than .sub.0 corresponds to a decrease in the oxygen content in the air, and thus reveals the existence of a leak on the cathode side of the stack. Particularly, analysis unit 76 stores value .sub.0 and compares measurement .sub.1 with value .sub.0 and diagnoses the leak on the cathode side if .sub.1<.sub.0.

(15) Within the measurement range of oxygen sensor 74, a quantification of the flow rate D.sub.f.sub.H2 of a hydrogen leak D.sub.f.sub.H2 is advantageously implemented by analysis unit 76 which stores value D.sub.Air according to the following relation:
D.sub.f.sub.H2=2.Math.(.sub.0.sub.1).Math.D.sub.Air

(16) Further, if the leak is located on the anode side, part of the anode mixture of oxygen-enriched air enters into enclosure 60, which causes an increase in the oxygen content in the gas analyzed by sensor 74. Thus, analysis unit 76 diagnoses the leak on the anode side if .sub.1>.sub.0.

(17) According to an embodiment, warning and/or alarm thresholds may be established and cause automatic actions on the electrolyzer control. For example, analysis unit 76 is capable of stopping the gas and current supply of the electrolyzer.

(18) An application of the invention to a high-temperature water vapor electrolyzer has been described. The invention also applies to a high-temperature co-electrolyzer supplied with a mixture of water vapor (H.sub.2O) and of carbon dioxide (CO.sub.2) and generating a mixture of hydrogen (H.sub.2) and of carbon monoxide (CO). In this case, the same lines of reasoning and formulas as previously should be applied, replacing the notion of hydrogen leak flow rate D.sub.f.sub.H2 with the notion of fuel gas H.sub.2+CO leak flow rate D.sub.f.sub.H2.sub.co.

(19) The invention also applies to a high-temperature solid oxide fuel cell formed of a stack of electrochemical elementary cells, such as previously described.

(20) In such a case, a leak on the fuel side or on the depleted air side results in both cases in a measured oxygen content lower than the oxygen content of the sweeping air. Analysis unit 76 thus diagnoses a leak as soon as .sub.1.sub.0.

(21) The invention applies to a reversible system, fuel cell and high-temperature electrolyzer. The use of an oxygen detector enables to detect a leak on the anode or cathode side in the hot area, with the advantage of allowing the identification of the defective side in electrolysis mode.

(22) The invention applies to previously-described systems operating at the atmospheric pressure, but also on pressurized systems. The oxygen detector may advantageously remain at the atmospheric pressure. The analysis is then performed on the gas coming out of the hot area, preferably after an expansion at the atmospheric pressure.

(23) Embodiments where the oxygen content of the air injected into the enclosure is a given constant quantity .sub.0, for example, the oxygen of air at the atmospheric pressure when air is injected, have been described. As a variation, oxygen content .sub.0 is measured to increase the accuracy of the detection, for example by arranging a device similar to elements 68, 70, 72, and 74 in the inlet duct. The second oxygen sensor is then connected to analysis unit 76 to deliver its measurement thereto.

(24) Comparisons (greater, smaller, different) between two values have been described. In a variation, the implemented comparisons use thresholds, a leak being detected when the oxygen content at the outlet .sub.1 differs from the initial oxygen content .sub.0 by more than a predetermined value, for example, that corresponding to the maximum hydrogen leak flow rate acceptable from an economical point of view. In a variation, different thresholds are applied according to the nature of the leak.

(25) An analysis device comprising a bypass and a pumping unit has been described. Such a configuration makes the oxygen measurement insensitive to the value of the sweeping air flow rate in the outlet duct of the enclosure, and thus allows a measurement, including for flow rates to strong for an oxygen measurement directly in the outlet duct. As a variation, if the sweeping air flow rate allows a direct measurement in the outlet duct, the measurement device comprises a sensor therein, optionally downstream of a droplet separator.