Assembly and method of using a fuel cell with an exchange membrane and an acid capture device

Abstract

An assembly comprising a proton exchange membrane fuel cell (1) having an anodic inlet (Ea), a cathodic inlet (Ec), an anodic outlet (Sa), and a cathodic outlet (Sc), said outlets (Sa, Sc) being configured to discharge exhaust gases (Ga, Gc) containing acid, the assembly comprising at least one acid capture device (2) mounted at at least one of the outlets (Sa, Sc) for extracting at least a portion of the acid present in the exhaust gases (Ga, Gc) and discharging deacidified exhaust gases (Ga*, Gc*). Abstract figure: Figure 2

Description

Title of the invention: Assembly and method for using an exchange membrane fuel cell and an acid capture device Technical field

[0001] The present invention relates to the field of fuel cells of the proton exchange membrane type known by its English abbreviation PEMFC for "Proton Exchange Membrane Fuel Cell". The invention relates in particular to a fuel cell intended to be installed in an aircraft, in particular, to power electrical equipment participating in the propulsion of the aircraft.

[0002] In a known manner, with reference to [Fig. 1], a fuel cell 1 comprises 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 while the cathode inlet Ec receives, for example, dioxygen in order to produce electricity at the terminals of the fuel cell 1 (not shown). Exhaust gases are discharged via the anode outlet Sa and the cathode outlet Sc.

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

[0004] The exhaust gases, which are evacuated by the anode outlet Sa and the cathode outlet Sc, contain mainly oxygen, nitrogen, hydrogen and water vapor but also traces of acid (a few ppm). For a high-temperature fuel cell, i.e. operating at temperatures between 120°C and 200°C, the exhaust gases have high temperatures and are corrosive due to the traces of acid, which is very restrictive for the equipment located downstream (valves Va, Vc, sensors, etc.), which reduces their service life.

[0005] Additional disadvantages also appear during the start / stop phases of the fuel cell 1. During these phases, the temperature of the fuel cell is lower than the operating temperature and the residual acid present in the exhaust pipes of the fuel cell 1 can crystallize and obstruct the anode outlet Sa and the cathode outlet Sc, the exhaust pipes Ca, Ce, as well as the equipment located downstream of the fuel cell 1. The crystallization of the acid can thus lead to corrosion, seizure or obstruction of certain exhaust pipes Ce, Ca and downstream equipment, which presents a inconvenience.

[0006] An immediate solution to eliminate this drawback is to propose membranes without acid doping. However, such a solution is not relevant since it penalizes proton conductivity. Another immediate solution is to use membranes that have better retention of phosphoric acid, but there are no mature and efficient technical solutions to date.

[0007] The invention aims to eliminate at least some of these drawbacks. PRESENTATION OF THE INVENTION

[0008] The 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 outlets being configured to discharge exhaust gases comprising acid.

[0009] The assembly is remarkable in that it comprises at least one acid capture device mounted at at least one of the outlets to extract at least part of the acid present in the exhaust gases and to evacuate deacidified exhaust gases.

[0010] Advantageously, an acid capture device is mounted at at least one of the outlets so as to extract the acid from the exhaust gases in order to avoid damage to downstream equipment such as a valve or a sensor. Thanks to the invention, the fuel cell is advantageously not modified, only an auxiliary acid capture device can be added in an exhaust line of the fuel cell.

[0011] Preferably, the acid capture device is mounted at the cathode outlet to extract at least a portion of the acid present in the cathode exhaust gases. This is advantageous since the cathode outlet is the source of the majority of acid discharges.

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

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

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

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

[0016] According to one aspect of the invention, the acid capture device comprises at least one control valve configured to control a passage or a bypass of the basic source. Thus, the valve makes it possible to control the consumption of the basic source sparingly.

[0017] Preferably, the valve is controllable, in particular, as a function of an operating parameter of the fuel cell. Thus, the regulation is advantageously automatic.

[0018] According to another aspect of the invention, the acid capture device comprises at least one condensation chamber comprising a liquid into which the exhaust gases are injected so as to condense and dilute the acid. Such a condensation chamber is advantageous since it makes it possible to optimally capture the water and acid present in the exhaust gases. In addition, such a condensation chamber makes it possible to optimally cool the exhaust gases, which is advantageous for a high-temperature fuel cell.

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

[0020] Preferably, the acid capture device comprises at least one circuit for sampling the gas phase from the condensation enclosure. Thus, deacidified gases can be evacuated downstream.

[0021] According to one aspect of the invention, the acid capture device comprises at least one heat exchanger configured to cool the deacidified exhaust gases. This is advantageous for a high-temperature fuel cell.

[0022] Preferably, a heat exchanger is mounted downstream of the basic source so as to avoid acid condensation which could damage the heat exchanger.

[0023] Preferably, the acid capture device comprises at least one phase separator configured to recover the liquid phase comprising the acid and the water from the exhaust gases and to discharge a deacidified gaseous phase.

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

[0025] Preferably, the assembly comprises a first acid capture device with a basic source mounted at the anode output and a second acid capture device with a condensation reservoir mounted at the cathode output. The use of two different capture devices makes it possible to adapt to the specificities of each fuel cell output.

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

[0027] The invention also relates to a method of using an assembly as presented previously, comprising steps consisting of: • extracting at least part of the acid present in the exhaust gases from at least one of the outlets of the fuel cell and • evacuate deacidified exhaust gases. PRESENTATION OF FIGURES

[0028] The invention will be better understood on reading the description which follows, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0029] [Fig.l] is a schematic representation of a fuel cell according to the prior art.

[0030] [Fig.2] is a schematic representation of an assembly of a fuel cell and two acid capture devices according to the invention.

[0031] [Fig. 3] is a schematic representation of a first embodiment of a capture device.

[0032] [Fig.4] is a schematic representation of a second embodiment of a capture device.

[0033] [Fig.5] is a schematic representation of a third embodiment of a capture device.

[0034] [Fig.6] is a schematic representation of a fourth embodiment of a capture device.

[0035] [Fig.7] is a schematic representation of a configuration of a fuel cell and two capture devices.

[0036] [Fig.8] is a schematic representation of a fifth embodiment of a capture device.

[0037] [Fig.9] is a schematic representation of a configuration of a fuel cell and two capture devices according to [Fig.8].

[0038] It should be noted that the figures set out the invention in detail for implementing the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0039] The invention relates to a fuel cell of the proton exchange membrane type known by its English abbreviation PEMFC for “Proton Exchange Fuel Cell Membrane”.

[0040] The invention will be presented for a high-temperature fuel cell, i.e. operating at temperatures between 120°C and 200°C, but the invention also applies to a low-temperature fuel cell operating at temperatures between 40°C and 100°C. The invention relates in particular to a fuel cell intended to be installed on board an aircraft, in particular, to power electrical equipment participating in the propulsion of said aircraft.

[0041] In a known manner, the fuel cell 1 comprises an anode inlet Ea, a cathode inlet Ec, an anode outlet Sa for anode exhaust gas Ga and a cathode outlet Sc for cathode exhaust gas Gc. The anode inlet Ea receives for example dihydrogen while the cathode inlet Ec receives for example dioxygen in order to produce electricity at the terminals of the fuel cell 1 (not shown). In this example, the fuel cell 1 comprises membrane electrode assemblies (MEA) comprising at least one membrane doped with acid, in particular phosphoric acid, so as to improve the proton conductivity of the membrane, preferably a solid polymer membrane which acts as an electrolyte.The exhaust gases Ga, Gc, which are evacuated through the anode outlet Sa and the cathode outlet Sc, contain mainly oxygen, nitrogen, hydrogen and water vapor but also traces of acid (a few ppm).

[0042] For a high-temperature fuel cell, i.e., operating at temperatures between 120°C and 200°C, the exhaust gases Ga, Gc are corrosive (pH of the order of 1.5 to 2) and have high temperatures. During tests carried out for a high-temperature fuel cell having an electrical power of 20 kW, the quantity of phosphoric acid lost in the exhaust gases Ga, Gc can reach 30 mg / hour depending on the operating conditions. Interestingly, it has been observed that nearly 90% of the acid discharges are made at the cathode outlet Sc. Such a fuel cell 1 is known to those skilled in the art and will not be presented in detail.

[0043] According to the invention, it is proposed to mount at least one acid capture device 2 at one or more of the anode Sa and cathode Sc outlets of the fuel cell 1 to extract at least a portion of the acid present in the exhaust gases Ga, Gc. In other words, the acid capture device 2 receives an exhaust gas Ga, Gc as an input and emits a deacidified exhaust gas Ga*, Gc* as an output.

[0044] Advantageously, the fuel cell 1 is not modified and the invention can be applied to fuel cells already in circulation.

[0045] In this example, with reference to [Fig.2], an anode exhaust pipe Ca connects the anode outlet Sa to an anode exhaust valve Va. In such a way analogously, a cathode exhaust line Ce connects the cathode outlet Sc to a cathode exhaust valve Vc. It goes without saying that other equipment could be mounted in the exhaust lines Ca, Ce, for example, sensors.

[0046] In this example, with reference to [Fig.2], an acid capture device 2 is mounted at each outlet Sa, Sc but it goes without saying that only one outlet Sa, Sc could be provided with an acid capture device 2. Preferably, the cathode outlet Sc is connected to such an acid capture device 2 given that most of the acid discharges come from the cathode as explained previously.

[0047] As will be presented in detail later, the acid capture device 2 can implement various technologies, in particular, a basic source 20 (Figures 3-5), a condensation enclosure 30 ([Fig.6]) or a phase separator 41 ([Fig.8]). The different technologies will be presented independently but it goes without saying that they could be coupled within the same acid capture device 2.

[0048] Subsequently, the various embodiments of the acid capture device 2 will be presented in relation to the anode output Sa for the sake of brevity but they apply to one or the other. The advantages linked to the use of a particular embodiment with the anode output Sa and / or the cathode output Sc will be presented individually.

[0049] With reference to [Fig. 3], according to a first embodiment, the acid capture device 2 comprises a basic source 20 configured to neutralize the acid present in the exhaust gases Ga. In a known manner, a basic source 20 naturally has a pH greater than 7, preferably greater than 11. Preferably, the basic source 20 comprises one or more of the following bases: NaOH, KOH and Ca(OH)2.

[0050] Preferably, the basic source 20 comprises an enclosure in which the base(s) is / are stored in solid and porous form. Such porosity advantageously allows the exhaust gases Ga to pass through the basic source 20 without disturbing the evacuation of the exhaust gases Ga. Upon contact with the base(s), the traces of acid are neutralized and trapped in the enclosure. Thus, the deacidified exhaust gases Ga* have a higher pH (ideally close to 7), which prevents damage to downstream equipment.

[0051] According to a variant, with reference to [Fig. 3], the acid capture device 2 comprises a pH indicator 21 configured to indicate the pH or pH range of the deacidified exhaust gas Ga*. Preferably, a visual indicator, in particular colorimetric, is used. Such a pH indicator 21 is advantageous for indicating that the basic source 20 is consumed and must be replaced. A pH close to of that of the acid indicates that it is necessary to replace the base contained in the basic source 20.

[0052] For a fuel cell 1 having an electrical power of 20 kW, the quantity of phosphoric acid discharged into the exhaust gases Ga, Gc can reach 30 mg / hour. The quantity of base necessary for the neutralization of this acid would therefore be of the order of 300 mg / hour; or 30 kg for 100 hours of operation.

[0053] According to a preferred aspect, with reference to [Fig. 4] representing a second embodiment, the acid capture device 2 comprises a control valve 22 comprising an inlet 221 connected to said anode outlet Sa, a first outlet 222 connected to an inlet of the basic source 20 and a second outlet 223 connected to an outlet of the basic source 20 so as to bypass it. The first outlet 222 is connected to the anode exhaust pipe Ca upstream of the basic source 20 while the second outlet 223 is connected to the anode exhaust pipe Ca downstream of the basic source 20.

[0054] Such a control valve 22 makes it possible to regulate the use of the basic source 20 in order to control its consumption. For example, the control valve 22 makes it possible to use the basic source 20 mainly during the start / stop phases of the fuel cell 1 and to leave it at rest during a nominal operating phase of the fuel cell 1.

[0055] Preferably, the control valve 22 is controllable, in particular, as a function of an operating parameter PAR of the fuel cell 1. For example, during the start / stop phases of the fuel cell 1, an operating parameter PAR is emitted by the fuel cell 1 (or by an associated computer) to activate deacidification by the basic source 20. Conversely, during a nominal operating phase of the fuel cell 1, an operating parameter PAR is emitted by the fuel cell 1 (or by an associated computer) to bypass the basic source 20. Thus, the basic source 20 is consumed sparingly.

[0056] The addition of a control valve 22 allowing bypass of the basic source 20 makes it possible to target the neutralization of the acid during specific operating phases, that is to say, when the risk of crystallization of the acid is greatest given the drop in temperature. Thus, depending on the application, the desired power, the mission profile of the aircraft and the mass / volume constraints, regular replacement operations of the basic source 20 are to be expected.

[0057] It is understood that a control valve 22 may be used in various embodiments of the capture device 2 so as to regulate the neutralization of the acid.

[0058] With reference to [Fig. 5], according to a third embodiment, the acid capture device 2 comprises a heat exchanger 23 which is configured to cool the deacidified exhaust gases Ga* preferably at a temperature below 80°C, which preserves downstream equipment. Preferably, the heat exchanger 23 is mounted downstream of the basic source 20 in order to avoid condensing acid which could damage the heat exchanger 23. Nevertheless, it goes without saying that the heat exchanger 23 could also be integrated into the basic source 20. The heat exchanger 23 can implement different cooling technologies (forced convection, liquid cooling, etc.).

[0059] The use of a basic source 20, according to one of the first three embodiments, is particularly suitable for the anode output Sa given that the proportion of water produced by the electrochemical reaction is negligible. The use of a basic source 20, of simple and practical design, is advantageous for treating a reduced quantity of liquid which will consume little of the basic source 20.

[0060] According to a fourth embodiment, with reference to [Fig. 6], the acid capture device 2 comprises a condensation chamber 30 comprising a liquid L, in particular water, into which the exhaust gases Ga from said outlet Sa are injected. Thus, the exhaust gases Ga are cooled during its injection into the liquid L, which makes it possible to condense the traces of acid but also the water present in the water vapor. The traces of acid can be extracted optimally by dilution in the liquid L.

[0061] As illustrated in [Fig.6], the acid capture device 2 comprises a cooling circuit (thickened 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. Liquid L heated in the condensation enclosure 30 is thus cooled by the heat exchanger 31 and then reinjected into the condensation enclosure 30 by the pump 32. The acid capture device 2 further comprises a circuit 33 for sampling the gaseous phase from the condensation enclosure 30 so as to recover the deacidified cooled gases Ga*.

[0062] The condensation enclosure 30 comprises an injector, immersed in the liquid, which comprises a diffuser 301, preferably cylindrical, allowing the diffusion by micro-leaks of the exhaust gases Ga into the liquid L, for example, through an alloy or a sintered ceramic. Advantageously, the acid (in particular phosphoric acid) is very soluble in hot water, which allows it to be trapped. Diffusion by micro-leaks increases the exchange surface and allows the exhaust gases Ga to be optimally cooled.

[0063] This embodiment is particularly suitable for the cathode outlet Sc whose cathode exhaust gases Gc comprise a large quantity of water vapor. The water in the water vapor is condensed in the condensation chamber 30, which increases the quantity of liquid L in the condensation chamber 30 during the time. For this purpose, an overflow device 34 is provided, here a valve connected to a purge circuit CP, allowing liquid L to be evacuated from the condensation enclosure 30 when the liquid level is too high. In this example, the overflow device 34 is also connected to the cooling circuit. The joint use of the cooling circuit and the overflow device 34 makes it possible to maintain a constant and temperature-regulated volume of water. For a fuel cell 1 with a power of 20 kW as presented previously, it is estimated that 11 liters of liquid water per hour can be recovered at the cathode outlet Sc if all the water vapor produced by the electrochemical reaction is recovered and condensed.

[0064] With reference to [Fig.7], a first configuration of a fuel cell 1 is shown in which the anode output Sa is associated with an acid capture device 2 comprising a basic source 20 in order to benefit from its small size and its simple design. Such a basic source 20 is suitable given that the proportion of water produced by the electrochemical reaction is low as is the quantity of acid discharges. The basic source 20 can thus be used sparingly. Conversely, the cathode output Sc is associated with an acid capture device 2 comprising a condensation enclosure 30 in order to benefit from its high efficiency for collecting the water produced by the electrochemical reaction as well as the acid discharges which are greater on the cathode side.

[0065] According to another embodiment, with reference to [Fig. 8], the acid capture device 2 comprises at least one phase separator 40 configured to recover the liquid phase comprising the traces of acid and the water and to allow the deacidified gaseous phase Ga* to pass. Preferably, the phase separator 40 is in the form of a condenser.

[0066] Preferably, the acid capture device 2 further comprises an acid storage tank 41 configured to collect the acidic 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 separators 40 could also be connected to a purge circuit. With reference to [Fig. 9], a second configuration of a fuel cell 1 is shown in which the anode outlet Sa and the cathode outlet Sc are both associated with phase separators 40 which are connected to an acid storage tank 41 which is common.

[0067] Thanks to the invention, during the operation of the fuel cell 1, the exhaust gases Ga, Gc are treated so as to extract at least a portion of the discharged acid. This makes it possible to protect the equipment, located downstream of the fuel cell 1, which receives deacidified and, preferably, cooled exhaust gases Ga*, Gc*.

Claims

Claims

1. An assembly comprising a proton exchange membrane fuel cell (1) comprising an anode inlet (Ea), a cathode inlet (Ec), an anode outlet (Sa) and a cathode outlet (Sc), said outlets (Sa, Sc) being configured to discharge exhaust gases (Ga, Gc) comprising acid, an assembly characterized in that it comprises at least one acid capture device (2) mounted at at least one of the outlets (Sa, Sc) to extract at least a portion of the acid present in the exhaust gases (Ga, Gc) and discharge deacidified exhaust gases (Ga*, Gc*).

2. An assembly according to claim 1, wherein the acid capture device (2) is mounted at the cathode outlet (Sc) to extract at least a portion of the acid present in the cathode exhaust gases (Gc).

3. An assembly according to claim 2, further comprising an acid capture device (2) mounted at the anode outlet (Sa).

4. Assembly according to one of claims 1 to 3, in which the acid capture device (2) comprises at least one basic source (20) configured to neutralize the acid present in the exhaust gases (Ga, Gc).

5. An assembly according to claim 4, wherein the basic source (20) comprises at least one base in solid and porous form.

6. An assembly according to one of claims 4 to 5, wherein the basic source (20) comprises one or more of the following bases: NaOH, KOH and Ca(OH)2.

7. Assembly according to one of claims 4 to 6, in which the acid capture device (2) comprises at least one control valve (22) configured to control a passage or a bypass of the basic source (20).

8. Assembly according to claim 7, in which the valve (22) is controllable, in particular, as a function of an operating parameter (PAR) of the fuel cell (1).

9. Assembly according to one of claims 1 to 8, in which the acid capture device (2) comprises at least one condensation enclosure (30) comprising a liquid (L) into which the exhaust gases (Ga, Gc) are injected so as to condense and dilute the acid.

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

11. Assembly according to one of claims 1 to 10, in which the acid capture device (2) comprises at least one heat exchanger (23) configured to cool the deacidified exhaust gases (Ga*, Gc*).

12. Assembly according to one of claims 1 to 11, in which the acid capture device (2) comprises at least one phase separator (40) configured to recover the liquid phase comprising the acid and the water from the exhaust gases (Ga, Gc) and to evacuate a deacidified gaseous phase.

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

14. An assembly comprising a first acid capture device (2) according to claim 4 mounted at the anode outlet (Sa) and a second acid capture device (2) according to claim 9 mounted at the cathode outlet (Sc).

15. Method of using an assembly according to one of claims 1 to 14, comprising steps consisting of: • extracting at least part of the acid present in the exhaust gases (Ga, Gc) from at least one of the outlets (Sa, Sc) of the fuel cell (1) and • discharging deacidified exhaust gases (Ga*, Gc*).

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