ASSEMBLY AND METHOD FOR USING EXCHANGE MEMBRANE FUEL CELLS AND ACID SCAPTURING DEVICES - Patent application

Abstract

An assembly comprising a proton exchange membrane fuel cell (1) with an anode inlet (Ea), a cathode inlet (Ec), an anode outlet (Sa) and a cathode outlet (Sc), said outlets (Sa, Sc) being configured to remove an acid-containing exhaust gas (Ga, Gc), the assembly being adapted to extract at least a portion of the acid present in the exhaust gas (Ga, Gc) and to produce an acid-free exhaust gas (Ga * , Gc * ) attached to at least one of the outlets (Sa, Sc).

Description

[Technical field]

[0001] The present invention relates to the field of fuel cells of the proton exchange membrane type, known as PEMFC, an abbreviation for "Proton-Exchange Membrane Fuel Cell". In particular, the present invention relates to fuel cells intended to be installed in aircraft, in particular to power the electrical equipment involved in the propulsion of the aircraft. [Background technology]

[0002] As is known, referring to FIG. 1, a fuel cell 1 includes an anode inlet Ea, a cathode inlet Ec, an anode outlet Sa, and a cathode outlet Sc. The anode inlet Ea receives, for example, dihydrogen, and the cathode inlet Ec receives, for example, dioxygen, to produce electricity at the terminals (not shown) of the fuel cell 1. Exhaust gas is discharged through the anode outlet Sa and the cathode outlet Sc.

[0003] Such a fuel cell 1 generally comprises a membrane electrode assembly (MEA) with a solid polymer membrane that serves as the electrolyte. To improve the proton conductivity of the membrane, it is known to dope the membrane with an acid, in particular phosphoric acid.

[0004] The exhaust gases discharged through the anode outlet Sa and the cathode outlet Sc contain mainly oxygen, nitrogen, hydrogen and water vapor, but also traces (a few ppm) of acids. For high-temperature fuel cells, i.e. those operating at temperatures between 120°C and 200°C, the exhaust gases have a high temperature and are corrosive due to traces of acids, which places a very high load on the downstream equipment (valves Va, Vc, sensors, etc.) and reduces their lifespan.

[0005] Further drawbacks also arise during the start-up / shutdown phases of the fuel cell 1. During these phases, the temperature of the fuel cell is lower than the operating temperature and residual acid in the exhaust line of the fuel cell 1 can crystallize and clog the anode outlet Sa and the cathode outlet Sc, the exhaust lines Ca, Cc and the equipment downstream of the fuel cell 1. Thus, acid crystallization can cause corrosion, failure or blockage of certain exhaust pipelines Cc, Ca and downstream equipment, which is a drawback.

[0006] An immediate solution to eliminate this drawback is to provide a membrane without acid doping. However, such a solution is inappropriate because it impairs proton conductivity. Another immediate solution is to use a membrane with better phosphoric acid retention, but at present there is no mature and efficient technical solution. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention therefore aims to eliminate at least some of these drawbacks. [Means for solving the problem]

[0008] The present invention relates to an assembly comprising a proton exchange membrane fuel cell comprising an anode inlet, a cathode inlet, an anode outlet and a cathode outlet, said outlet being configured to release an acid-containing exhaust gas.

[0009] The assembly is notable in that it includes at least one acid trapping device attached to at least one of the outlets for extracting at least a portion of the acids present in the exhaust gas and releasing an acid-depleted exhaust gas.

[0010] Advantageously, an acid scavenging device is fitted to at least one of the outlets to extract acid from the exhaust gas to avoid damage to downstream equipment such as valves, sensors, etc. Advantageously, the invention leaves the fuel cell unchanged, requiring only the addition of an auxiliary acid scavenging device in the exhaust line of the fuel cell.

[0011] Preferably, an acid scavenging device is fitted to the cathode outlet to extract at least a portion of the acids present in the cathode exhaust gas, which is advantageous as the cathode outlet is responsible for the majority of the acid emissions.

[0012] According to one aspect of the present invention, the assembly further comprises an acid trapping device attached to the anode outlet. In other words, a first acid trapping device is attached to the anode outlet and a second acid trapping device is attached to the cathode outlet. Thus, all the acid waste is treated.

[0013] According to one aspect of the invention, the acid capture device comprises at least one base source configured to neutralize the acids present in the exhaust gas, the base source advantageously making it possible to extract the acids by neutralizing them with the base source, compensating for acidity by addition of base.

[0014] Preferably, the base source comprises at least one base in solid and porous form, as such a base source is simple to implement and is advantageous for exhaust gases having a low water vapor content.

[0015] Preferably, the base source comprises one or more of the following bases: NaOH, KOH, and Ca2. Such bases are easy and convenient to handle.

[0016] According to one aspect of the invention, the acid scavenging device comprises at least one regulating valve configured to control the passage or bypass of the base source, which thus makes it possible to economize and control the consumption of the base source.

[0017] Preferably, the valve is controllable, in particular according to the operating parameters of the fuel cell, so that the regulation is advantageously automatic.

[0018] According to another aspect of the invention, the acid capture device comprises at least one condensation enclosure with a liquid into which the exhaust gas is injected so as to condense and dilute the acid. Such a condensation chamber is advantageous as it allows optimal capture of water and acid in the exhaust gas. Furthermore, such a condensation chamber allows optimal cooling of the exhaust gas, which is advantageous for high-temperature fuel cells.

[0019] Preferably, the acid scavenging device comprises at least one cooling circuit configured to cool the liquid in the condensation enclosure to achieve optimal condensation over time.

[0020] Preferably, the acid trapping device comprises at least one sampling circuit of the gas phase of the condensation enclosure, so that the acid-depleted gas can be released downstream.

[0021] According to one aspect of the invention, the acid scavenging device comprises at least one heat exchanger configured to cool the acid-depleted exhaust gas, which is advantageous for high temperature fuel cells.

[0022] Preferably, the heat exchanger is installed downstream of the base source to avoid condensation of the acid which could damage the heat exchanger.

[0023] Preferably, the acid capture device comprises at least one phase separator configured to recover a liquid phase comprising acid and water from the exhaust gas and to release an acid-depleted gas phase.

[0024] Preferably, the acid scavenging device comprises at least one acid storage tank configured to collect the liquid phase.

[0025] Preferably, the assembly comprises a first acid scavenging device comprising a base source attached to the anode outlet and a second acid scavenging device comprising a condensation tank attached to the cathode outlet. The use of two different scavenging devices allows for adaptation to the specifications of each fuel cell outlet.

[0026] Preferably, the fuel cell comprises at least one membrane doped with an acid, in particular phosphoric acid.

[0027] The present invention further provides a method of using the assembly as described above, comprising the steps of: - extracting at least a portion of the acid in the exhaust gas from at least one of the outlets of the fuel cell; - releasing the acid-removed exhaust gas; The present invention relates to a method comprising the steps of:

[0028] The invention will be better understood by reading the following description, given by way of example, and by referring to the following figures, given by way of non-limiting example, in which similar objects are provided with the same reference symbols: [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell according to the prior art. [Diagram 2] FIG. 2 is a schematic diagram of an assembly of a fuel cell and two acid scavenging devices according to the present invention. [Diagram 3] FIG. 1 is a schematic diagram of a first embodiment of a capture device. [Figure 4] FIG. 2 is a schematic diagram of a second embodiment of a capture device. [Diagram 5] FIG. 13 is a schematic diagram of a third embodiment of a capture device. [Figure 6] FIG. 13 is a schematic diagram of a fourth embodiment of a capture device. [Figure 7] FIG. 1 is a schematic diagram of a configuration of a fuel cell and two capture devices. [Figure 8] FIG. 13 is a schematic diagram of a fifth embodiment of a capture device. [Figure 9] FIG. 9 is a schematic diagram of a configuration of a fuel cell and two capture devices according to FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] It should be noted that the drawings represent the invention in detail for the purpose of implementing the invention, and of course, where applicable, said drawings can be used to better define the invention.

[0031] The present invention relates to fuel cells of the proton exchange membrane type, known as PEMFC, an abbreviation for "Proton-Exchange Membrane Fuel Cell".

[0032] Although the invention is presented with respect to high-temperature fuel cells, i.e. fuel cells operating at temperatures between 120° C. and 200° C., the invention also applies to low-temperature fuel cells operating at temperatures between 40° C. and 100° C. In particular, the invention relates to fuel cells intended to be installed in aircraft, in particular for powering the electrical equipment involved in the propulsion of said aircraft.

[0033] In a known manner, the fuel cell 1 comprises an anode inlet Ea, a cathode inlet Ec, an anode outlet Sa for the anode exhaust gas Ga, and a cathode outlet Sc for the cathode exhaust gas Gc. The anode inlet Ea receives, for example, dihydrogen and the cathode inlet Ec receives, for example, dioxygen, in order to produce electricity at the terminals (not shown) of the fuel cell 1. In this example, the fuel cell 1 comprises a membrane electrode assembly (MEA) comprising at least one membrane, preferably a solid polymer membrane acting as an electrolyte, doped with an acid, in particular phosphoric acid, to improve the proton conductivity of the membrane. The exhaust gases Ga, Gc discharged via the anode outlet Sa and the cathode outlet Sc mainly contain oxygen, nitrogen, hydrogen and water vapor, but also traces (a few ppm) of acids.

[0034] In the case of high-temperature fuel cells, i.e. fuel cells operating at temperatures between 120° C. and 200° C., the exhaust gases Ga, Gc are corrosive (pH of about 1.5 to 2) and have high temperatures. During tests carried out on a high-temperature fuel cell with an electrical power of 20 kW, the amount of phosphoric acid lost in the exhaust gases Ga, Gc can reach up to 30 mg / h depending on the operating conditions. Interestingly, it has been observed that almost 90% of the acid release occurs at the cathode outlet Sc. Such fuel cells 1 are known to those skilled in the art and will not be presented in more detail.

[0035] According to the invention, it is proposed to attach at least one acid capture device 2 to one or more of the anode Sa and cathode Sc outlets of the fuel cell 1 in order to extract at least a portion of the acids present in the exhaust gases Ga, Gc. In other words, the acid capture device 2 receives the exhaust gases Ga, Gc at the inlet and extracts the acid-free exhaust gas Ga * , Gc * is discharged.

[0036] Advantageously, the fuel cell 1 is not modified, allowing the invention to be applied to fuel cells already in circulation.

[0037] In this example, referring to FIG. 2, an anode exhaust line Ca connects the anode outlet Sa to the anode exhaust valve Va. Similarly, a cathode exhaust line Cc connects the cathode outlet Sc to the cathode exhaust valve Vc. It goes without saying that other devices, such as sensors, can be attached to the exhaust lines Ca and Cc.

[0038] In this example, with reference to FIG. 2, an acid scavenging device 2 is attached to each outlet Sa, Sc, although it will be appreciated that only one outlet Sa, Sc may be provided with an acid scavenging device 2. Preferably, the cathode outlet Sc is connected to such an acid scavenging device 2, since, as explained previously, most acid release occurs from the cathode.

[0039] As will be presented in detail later, the acid scavenging device 2 can realize various techniques, in particular a base source 20 (FIGS. 3 to 5), a condensation enclosure 30 (FIG. 6), or a phase separator 41 (FIG. 8). Although the various techniques are presented independently, it goes without saying that they can be combined within the same acid scavenging device 2.

[0040] Below, for the sake of brevity, various embodiments of the acid scavenging device 2 are presented in relation to the anode outlet Sa, but they apply to either one or the other. Advantages associated with the use of particular embodiments having an anode outlet Sa and / or a cathode outlet Sc are presented separately.

[0041] Referring to FIG. 3, according to a first embodiment, the acid capture device 2 comprises a base source 20 configured to neutralize acids present in the exhaust gas Ga. In a known manner, the base source 20 inherently has a pH greater than 7, preferably greater than 11. Preferably, the base source 20 comprises one or more of the following bases: NaOH, KOH, and Ca(OH)2.

[0042] Preferably, the base source 20 comprises an enclosure in which the base is stored in a solid and porous form. Such porosity advantageously allows the exhaust gas Ga to pass through the base source 20 without impeding the release of the exhaust gas Ga. Upon contact with the base, traces of acid are neutralized and trapped within the enclosure. As a result, the acid-free exhaust gas Ga is discharged. * has a higher pH (ideally closer to 7), which prevents damage to downstream equipment.

[0043] According to one variant, referring to FIG. 3, the acid capture device 2 captures the acid-free exhaust gas Ga *The base source 20 is provided with a pH indicator 21 configured to indicate a pH or pH range of the base source 20. Preferably, a visual indicator, in particular a colorimetric indicator, is used. Such a pH indicator 21 is advantageous to indicate that the base source 20 is consumed and must be replaced. A pH close to the acid pH indicates that the base contained in the base source 20 must be replaced.

[0044] For a fuel cell 1 with an electrical output of 20 kW, the amount of phosphoric acid released in the exhaust gases Ga, Gc can be up to 30 mg / h. The amount of base required to neutralize this acid therefore amounts to approximately 300 mg / h, i.e. 30 kg for 100 hours of operation.

[0045] According to a preferred embodiment, referring to FIG. 4 showing a second embodiment, the acid scavenging device 2 includes an adjusting valve 22 having an inlet 221 connected to the anode outlet Sa, a first outlet 222 connected to the inlet of the base source 20, and a second outlet 223 connected to the outlet of the base source 20 to bypass the base source 20. The first outlet 222 is connected to the anode exhaust line Ca upstream of the base source 20, and the second outlet 223 is connected to the anode exhaust line Ca downstream of the base source 20.

[0046] Such a regulating valve 22 makes it possible to regulate the use of the base source 20 in order to control its consumption. By way of example, the regulating valve 22 makes it possible to use the base source 20 mainly during start-up / shutdown phases of the fuel cell 1 and to keep the base source 20 switched off during nominal operating phases of the fuel cell 1.

[0047] Preferably, the regulating valve 22 is controllable in particular according to an operating parameter PAR of the fuel cell 1. For example, during start-up / shutdown phases of the fuel cell 1, the operating parameter PAR is issued by the fuel cell 1 (or by an associated computer) to activate the removal of acid by the base source 20. Conversely, during nominal operating phases of the fuel cell 1, the operating parameter PAR is issued by the fuel cell 1 (or by an associated computer) to bypass the base source 20. The base source 20 is thus consumed sparingly.

[0048] The addition of a regulating valve 22 allowing the bypass of the base source 20 makes it possible to target the neutralization of the acid during certain operational phases, i.e. when the risk of acid crystallization is greatest given the temperature drop. Periodic replacement operations of the base source 20 should therefore be planned according to the application, the desired power, the aircraft mission profile and the mass / volume constraints.

[0049] Of course, a regulating valve 22 can be used in various embodiments of the capture device 2 to regulate the neutralization of the acid.

[0050] Referring to FIG. 5, according to the third embodiment, the acid trapping device 2 traps the exhaust gas Ga * to a temperature preferably below 80° C., which protects downstream equipment. Preferably, the heat exchanger 23 is mounted downstream of the base source 20, in order to avoid condensation of the acid, which may damage the heat exchanger 23. It goes without saying that the heat exchanger 23 can nevertheless also be integrated in the base source 20. The heat exchanger 23 can realize different cooling techniques (forced convection, liquid cooling, etc.).

[0051] The use of a base source 20 according to one of the first three embodiments is particularly suitable for the anode outlet Sa, since the proportion of water produced by the electrochemical reaction is negligible. The use of a base source 20 of simple and convenient design is advantageous for treating a reduced amount of liquid, which consumes little of the base source 20.

[0052] According to a fourth embodiment, with reference to [FIG. 6], the acid capture device 2 comprises a condensation enclosure 30 containing a liquid L, in particular water, into which the exhaust gas Ga at said outlet Sa is injected. The exhaust gas Ga is thus cooled when injected into the liquid L, which makes it possible to condense not only traces of acid, but also the water present in the water vapor. Traces of acid can be optimally extracted by dilution in the liquid L.

[0053] As shown in FIG. 6, the acid capture device 2 comprises a cooling circuit (bold line) configured to cool the liquid L in the condensation enclosure 30. In this example, the cooling circuit comprises a heat exchanger 31 and a pump 32. Thus, the liquid L heated in the condensation chamber 30 is cooled by the heat exchanger 31 and then pumped back into the condensation chamber 30 by the pump 32. The acid capture device 2 is configured to cool the acid-free cooled gas Ga * A sampling circuit 33 for sampling the gas phase of the condensation chamber 30 is further provided for collecting

[0054] The condensation enclosure 30 comprises an injector immersed in the liquid, which preferably comprises a cylindrical diffuser 301, allowing diffusion by microleak of the exhaust gas Ga into the liquid L, for example through an alloy or sintered ceramic. Advantageously, acids (especially phosphoric acid) have a high solubility in hot water, which allows the acid to be trapped. The microleak diffusion increases the exchange area and allows optimal cooling of the exhaust gas Ga.

[0055] This embodiment is particularly suitable for cathode outlets Sc, where the cathode exhaust gas Gc contains a large amount of water vapor. Water from the water vapor is condensed in the condensation enclosure 30, which increases the amount of liquid L in the condensation enclosure 30 over time. For this purpose, an overflow device 34, here a valve connected to the purge circuit CP, is provided, allowing the liquid L to be discharged from the condensation chamber 30 when the liquid level is too high. In this example, the overflow device 34 is also connected to a cooling circuit. The cooling circuit in combination with the overflow device 34 makes it possible to maintain a constant temperature-controlled volume of water. For a fuel cell 1 with a power of 20 kW as described above, it is estimated that 11 liters of liquid water per hour can be recovered at the cathode outlet Sc, if all the water vapor created by the electrochemical reaction is recovered and condensed.

[0056] Referring to FIG. 7, a first configuration of a fuel cell 1 is shown, in which the anode outlet Sa is associated with an acid capture device 2 with a base source 20 in order to benefit from the small size and simple design of the base source 20. Such a base source 20 is suitable under the premise that the proportion of water produced by the electrochemical reaction is low and the amount of acid released is also small. Therefore, the base source 20 can be used economically. Conversely, the cathode outlet Sc is associated with an acid capture device 2 with a condensation enclosure 30 in order to benefit from the high efficiency of the condensation enclosure 30 in collecting the water produced by the electrochemical reaction and the higher acid release on the cathode side.

[0057] According to another embodiment, referring to FIG. 8, the acid capture device 2 collects a liquid phase containing traces of acid and water, and collects a gas phase Ga from which the acid has been removed. * The at least one phase separator 40 is configured to allow the passage of the phase separator 40. Preferably, the phase separator 40 is in the form of a condenser.

[0058] Preferably, the acid capture device 2 further comprises an acid storage tank 41 configured to collect the acid liquid phase from one or more phase separators 40. In practice, the most acidic pH at the cathode outlet is 4.5. It goes without saying that the phase separator 40 can also be connected to a purge circuit. With reference to FIG. 9, a second configuration of the fuel cell 1 is shown, in which both the anode outlet Sa and the cathode outlet Sc are associated with a phase separator 40 connected to a common acid storage tank 41.

[0059] According to the invention, during operation of the fuel cell 1, the exhaust gases Ga, Gc are treated to extract at least a portion of the released acid. This allows the acid-free, preferably cooled exhaust gas Ga * , Gc * This makes it possible to protect the device receiving the signal.

Claims

1. An assembly comprising a proton exchange membrane fuel cell (1) with an anode inlet (Ea), a cathode inlet (Ec), an anode outlet (Sa) and a cathode outlet (Sc), said outlets (Sa, Sc) being configured to release acid-containing exhaust gases (Ga, Gc), the assembly being adapted to extract at least a portion of the acid in the exhaust gases (Ga, Gc) and to produce an acid-free exhaust gas (Ga ＊ , Gc ＊ Assembly, characterized in that it comprises at least one acid scavenging device (2) attached to at least one of the outlets (Sa, Sc) for releasing acid.

2. Assembly according to claim 1, wherein an acid capture device (2) is attached to the cathode outlet (Sc) to extract at least a portion of the acids present in the cathode exhaust gas (Gc).

3. 3. The assembly according to claim 2, further comprising an acid scavenging device (2) attached to the anode outlet (Sa).

4. Assembly according to claim 1, wherein the acid scavenging device (2) comprises at least one base source (20) configured to neutralize acids present in the exhaust gas (Ga, Gc).

5. 5. The assembly of claim 4, wherein the base source (20) comprises at least one base in solid and porous form.

6. 5. The assembly of claim 4, wherein the base source (20) comprises one or more of the following bases: NaOH, KOH, and Ca(OH)2.

7. 5. The assembly of claim 4, wherein the acid scavenging device (2) comprises at least one regulating valve (22) configured to control the passage or bypass of the base source (20).

8. 8. An assembly according to claim 7, wherein the valve (22) is controllable, in particular according to the operating parameters (PAR) of the fuel cell (1).

9. Assembly according to claim 1, wherein the acid trapping device (2) comprises at least one condensation enclosure (30) with a liquid (L) into which the exhaust gases (Ga, Gc) are injected so as to condense and dilute the acid.

10. 10. The assembly according to claim 9, wherein the acid trapping device (2) comprises at least one cooling circuit configured to cool the liquid (L) of the condensation enclosure (30).

11. The acid capture device (2) captures the acid-removed exhaust gas (Ga ＊ , Gc ＊ 2. The assembly of claim 1, further comprising at least one heat exchanger (23) configured to cool the

12. 2. The assembly according to claim 1, wherein the acid capture device (2) comprises at least one phase separator (40) configured to recover a liquid phase comprising acid and water from the exhaust gas (Ga, Gc) and to release an acid-depleted gas phase.

13. Assembly according to claim 12, wherein the acid scavenging device (2) comprises at least one acid storage tank (41) configured to collect the liquid phase.

14. 10. An assembly comprising a first acid scavenging device (2) according to claim 4 attached to an anode outlet (Sa) and a second acid scavenging device (2) according to claim 9 attached to a cathode outlet (Sc).

15. A method of using an assembly according to any one of claims 1 to 14, comprising the steps of: Extracting at least a portion of the acids present in the exhaust gas (Ga, Gc) from at least one of the outlets (Sa, Sc) of the fuel cell (1); Acid-removed exhaust gas (Ga ＊ , Gc ＊ ) and A method comprising the steps of:

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