FUEL CELL AND PURGE PROCESS

Abstract

FUEL CELL AND PURGE PROCESS The fuel cell (10) comprises: - a programmable controller, - a cathode (20) with a fluid inlet duct (40), a fluid outlet duct (50), and a bypass duct (60) between the inlet and outlet ducts, the bypass duct (60) comprising a first valve (70) controllable by the controller. The controller is programmed to implement a cathode (20) purge process, said process comprising: - a first step during which the first valve (70) is opened, - a second step (190) following the first step, during which the first valve (70) is closed. Figure for the abbreviation: 2

Description

Title of the invention: FUEL CELL AND PURGE METHOD

[0001] TECHNICAL FIELD AND PRIOR TECHNOLOGY

[0002] The present invention relates to a hydrogen cell or fuel cell which allows to produce electrical energy from hydrogen and oxygen. In a proton exchange membrane fuel cell, a membrane is surrounded by two electrodes and preferably includes an electrolyte and a catalyst. Hydrogen (H2) is supplied to one of the two electrodes, forming the anode. It decomposes into two hydrogen protons (H+) and two electrons (e-). The two H+ protons pass through the membrane to the other side, forming the cathode, and encounter oxygen (O2). The oxygen is preferably supplied in the form of air, but any other fluid containing oxygen could be used. The electrons travel to the cathode via a circuit, allowing the corresponding electrical energy to be recovered. At the cathode, these electrons reduce the oxygen (O2) to two oxygen ions (O2-): O2 + 4 e- → 2 O2-. Water is formed by the combination of these two oxygen ions with the two hydrogen protons.During operation, the products exiting the cathode side consist mainly of water and some unconsumed oxygen.

[0003] When the fuel cell is shut down, the supply of hydrogen and oxygen is cut off. Advantageously, the fuel cell is isolated from its environment with respect to fluid exchange. Due to the properties of the membrane, hydrogen continues to migrate from the anode to the cathode inside the cell.

[0004] This process stops when the partial pressure of hydrogen on both sides of the membrane reaches equilibrium. As a result, a high concentration of hydrogen is found at the cathode when the fuel cell starts up. This high concentration of hydrogen is potentially dangerous if it escapes, for example, into a car's exhaust system.

[0005] It is therefore necessary to ensure that the concentration of hydrogen exiting the cathode of the fuel cell remains below a threshold.

[0006] This threshold is typically the threshold below which there is no risk of explosion. Description of the invention

[0007] It is therefore an object of the present invention to provide a fuel cell comprising:

[0008] - a programmable controller,

[0009] - a cathode with a fluid inlet conduit, a fluid outlet conduit and a bypass duct between the inlet duct and the outlet duct,

[0010] - the bypass duct comprising a first valve controllable by the controller,

[0011] - the controller being programmed to implement a purging process of the cathode, said process comprising:

[0012] - a first step during which the first valve is opened,

[0013] - a second step following the first step, during which the first valve is closed.

[0014] The fuel cell may also have one or more of the following characteristics, considered individually or in all technically possible combinations:

[0015] - the outlet conduit includes a second valve controllable by the controller, the bypass conduit establishing a fluidic connection between

[0016] - a part of the inlet duct and

[0017] - a portion of the outlet conduit located downstream of the second valve;

[0018] - the second valve is closed during a first sub-step of the first step;

[0019] - the second valve is open during the second step;

[0020] - the first step includes a second sub-step of hunting between the first sub-stage and the second stage, the first valve and the second valve being open during the second sub-stage of the hunt;

[0021] - the controller controls the first valve and the second valve so that, between the end of the first sub-step and the beginning of the second step:

[0022] - a first flow rate of fluid circulating in the bypass duct decreases gradually and / or

[0023] - a second flow of fluid passing through the cathode gradually increases;

[0024] - the controller measures a hydrogen concentration in the outlet duct and compares the measured concentration with a threshold, and the controller initiates the second step when the measured hydrogen concentration is below said threshold;

[0025] - the bypass duct includes a calibrated vent between the inlet duct and the first valve;

[0026] - the fuel cell includes an anode, and the controller is programmed to circulate hydrogen on the anode side following the end of the cathode purging process.

[0027] According to a second aspect, the invention relates to a method for purging the cathode of a fuel cell having the above characteristics, comprising the following operations:

[0028] - in a first operation, the opening of the first valve;

[0029] - in a second operation, starting up a compressor in order to bring in a fluid in the inlet duct.

[0030] The process may also have one or more of the following characteristics, considered individually or in all technically possible combinations:

[0031] - the purging process includes an operation of closing the second valve before starting the compressor;

[0032] - the purging process includes a 3rd operation of opening the second valve, this opening should preferably be gradual;

[0033] - the purging process includes a 4th operation of closing the first valve, this closure should preferably be gradual;

[0034] - the purging process includes, in a 5th operation, a circulation of hydrogen via the anode of the fuel cell.

[0035] According to a third aspect, the invention relates to a computer program comprising instructions which lead the fuel cell having the above characteristics to execute the steps of the method having the above characteristics. Brief description of the drawings

[0036] The present invention will be better understood on the basis of the following description and the accompanying drawings in which:

[0037] [Fig-1] [Fig.1] shows a fuel cell according to a first example of realization.

[0038] [Fig.2] [Fig.2] shows a fuel cell according to a second example of realization.

[0039] [Fig.3] [Fig.3] shows a fuel cell according to a third example of realization.

[0040] [Fig.4] [Fig.4] shows a flow entering the mixer from the conduit of exit.

[0041] [Fig.5] [Fig.5] shows a flow passing through the bypass conduit.

[0042] [Fig.6] [Fig.6] shows a flow passing through the cathode of the fuel cell.

[0043] [Fig.7] [Fig.7] shows a flow of hydrogen passing through the cathode of the fuel cell fuel.

[0044] [Fig.8] [Fig.8] shows a composition of the fluid exiting through the mixer outlet.

[0045] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0046] Figure 1 shows a fuel cell (10) comprising a programmable controller (not shown). The fuel cell comprises a cathode side (20) and an anode side (30).

[0047] The cathode-forming side comprises a fluid inlet conduit (40) and a fluid outlet conduit (50). The anode-forming side comprises a hydrogen inlet conduit (130) and a hydrogen outlet conduit (140). The hydrogen outlet conduit (140) joins the fluid outlet conduit (50) in a mixer (150), which has an outlet (160).

[0048] A bypass conduit (60) is located between the fluid inlet conduit (40) and outlet conduit (50).

[0049] This bypass conduit includes a first valve (70). The bypass conduit may also include a calibrated vent (110) between the fluid inlet conduit (40) and the first valve (70).

[0050] The calibrated vent (110) is for example intended to expel the fluid to the outside in case of overpressure in the bypass conduit (60).

[0051] The fuel cell may also include a fluid humidifier (170) and a fluid compressor (120). The humidifier allows for moisture exchange between the fluid inlet and outlet lines.

[0052] The compressor allows a fluid to enter the inlet conduit (40) efficiently. The fluid is thus pressurized and / or a flow rate of the fluid (mass of fluid per unit time, M / T) is controlled.

[0053] Preferably, said fluid comprises air.

[0054] The fuel cell includes a second valve (80) located in the fluid outlet conduit (50). In this case, a portion of the outlet conduit located upstream (90) of the second valve can be distinguished from a portion of the outlet conduit located downstream (100) of the second valve: The upstream portion (90) is located between the cathode (20) and the second valve (80), the downstream portion (100) is located between the second valve (80) and the mixer (150).

[0055] The programmable controller is capable of and programmed to control the operation of the fuel cell. Thus, said controller controls at least the first valve (70), which can be open, closed, or in an intermediate state between "open" and "closed". The controller also controls the second valve between an "open", "closed", and "intermediate" state.

[0056] By "open," we mean a state in which the valve is fully open. By "closed," we mean a state in which the valve is closed so that no more fluid passes through. In an "intermediate" state, the fluid can still pass through the valve, but the valve offers resistance to the fluid. Thus, in the "intermediate" state, the valve offers greater resistance to the fluid than in the "open" state.

[0057] In operation, the fuel cell provides electricity, resulting from the reaction of the fluid at the cathode (20) with hydrogen arriving at the anode (30).

[0058] During operation, the first valve (70) is closed. The fluid enters the cathode (20) of the fuel cell through the inlet duct (40). Advantageously, the compressor (120) delivers the fluid at a controlled flow rate (mass per unit time). Simultaneously, hydrogen enters the anode side of the fuel cell (10) through the hydrogen inlet duct (130). Through the membrane (210), the hydrogen on the anode side (30) reacts with oxygen from the fluid, which arrives at the cathode side (20). Any remaining hydrogen, unconsumed during the reaction with the oxygen in the fluid, exits the anode and enters the hydrogen outlet duct (140). This remaining hydrogen is then conveyed to the mixer (150).

[0059] On the cathode side (20), a residual fluid, mixed with water vapor, exits. This mixture enters the fluid outlet conduit (50) and is conveyed to the mixer (150). The mixer blends the fluids arriving through the fluid outlet conduit (50) and the hydrogen outlet conduit (140), and the mixture exits through the outlet (160).

[0060] In the event that a humidifier (170) is present, it extracts some of the water vapor from the fluid contained in the fluid outlet duct (50) and transfers it to the fluid contained in the fluid inlet duct (40), where the extracted water is mixed with the fluid flowing towards the cathode of the fuel cell.

[0061] In a stopped state of the fuel cell, the fluid flow through the fluid inlet and the hydrogen flow through the hydrogen inlet are stopped. The hydrogen inlet (130) and hydrogen outlet (140) can be closed. If the second valve (80) is present, it can be closed.

[0062] During this shutdown state, the hydrogen remaining on the anode side passes through the membrane (210) and accumulates on the cathode side of the cell.

[0063] When the fuel cell is started from a standstill and without prior purging, the fluid entering through the inlet duct (40) pushes the hydrogen accumulated on the cathode side into the fluid outlet duct (50). This hydrogen then exits through the mixer outlet (160). In other words, a high concentration of hydrogen exits the mixer outlet (160). This is a potentially dangerous effect that must be avoided. For example, in an automotive application, the mixer outlet is connected to an exhaust pipe, which vents outside the car. In this case, the hydrogen can create a hazard in the immediate vicinity of the car, for example, through combustion or explosion.

[0064] The fuel cell cathode purging process ensures that the hydrogen concentration at the mixer outlet (160) remains below a threshold predetermined. The fuel cell controller is programmed to implement this purging process.

[0065] The purging process is implemented starting from the fuel cell when it is stopped. This process precedes the fuel cell's operating state. Preferably, the purging process is implemented before hydrogen is circulated to the anode side.

[0066] In a first step of this purging process, the first valve (70) is in the "open" state.

[0067] Part of the fluid conveyed by the inlet conduit (40) thus circulates, without passing through the cathode, through the bypass conduit to reach the outlet conduit (50).

[0068] Another part of the fluid conveyed through the inlet conduit (40) flows into the cathode, then into the outlet conduit (50).

[0069] During this first stage, the accumulated hydrogen, which enters the outlet duct (50) from the cathode (20), is diluted by the fluid passing through the bypass duct. In other words, the hydrogen concentration in the downstream section (100) is reduced due to mixing with the fluid arriving from the bypass duct (60). This results in a significantly reduced hydrogen concentration, which no longer poses a danger.

[0070] Preferably, the controller starts the compressor (120) during said first step. The mixing between the fluid passing through the bypass duct and the hydrogen exiting the cathode is then even more efficient.

[0071] Following the first step, the controller implements a second step, during which the first valve (70) is closed. Preferably, the second step is initiated by the controller when, following cathode purging, the hydrogen concentration in the outlet duct has fallen below a threshold. The controller can also measure the hydrogen concentration in the outlet duct and compare it with a threshold. The controller initiates the second step when the hydrogen concentration has fallen below said threshold.

[0072] According to a preferred embodiment, the fluid outlet conduit (50) includes a second valve (80).

[0073] The bypass conduit (60) is provided between the fluid inlet conduit (40) and the portion of the fluid outlet conduit (50) located upstream (90) of said second valve (80). This embodiment is illustrated in [Fig. 1]. In this case, the second valve (80) is open during the first step as well as during the second step.

[0074] Alternatively, as illustrated in [Fig.2], the bypass conduit (60) is provided between the fluid inlet conduit (40) and the portion of the outlet conduit located downstream (90) of the second valve and upstream of the mixer (150).

[0075] Figure 3 shows the same configuration as Figure 2, but with a humidifier (170) positioned differently. Thus, the humidifier can be placed to allow moisture transport from a portion of the outlet duct located upstream of the second valve to a portion of the inlet duct (40) located before the bypass duct.

[0076] In the embodiment according to [Fig. 2] or 3, the second valve (80) is preferably closed during a first substep (180) of the first step. Closing the second valve during the first substep establishes a stable fluid flow through the inlet conduit (40), the bypass conduit (60), and the downstream portion of the outlet conduit. With the second valve closed, the hydrogen accumulated on the cathode side is not forced into the outlet conduit (50) during the first substep.

[0077] Following the establishment of a stable fluid flow during the first substep (180), the controller can implement a second flushing substep (200) before the second step (190). During the second flushing substep (200), the first valve (70) and the second valve (80) are opened. A portion of the fluid entering through the inlet pipe passes through the bypass pipe. A second portion of the fluid entering through the inlet pipe passes through the cathode. This second portion of the fluid pushes the hydrogen that has accumulated in the cathode toward the outlet pipe (50). In the outlet pipe, the hydrogen mixes with the first portion of the fluid that passed through the bypass pipe. The hydrogen concentration is thus reduced. A significantly reduced hydrogen concentration exits the mixer outlet.

[0078] The embodiment shown in [Fig. 2] advantageously allows for precise control of the two flows, one passing through the bypass duct and the other through the fuel cell cathode. This precise control enables reliable monitoring of the hydrogen concentration in the downstream section (100) of the outlet duct and in the mixer outlet (160).

[0079] Thus, following the first substep (180) and up to the beginning of the second step (190), the controller can control the first and second valves so that a first flow rate of fluid through the bypass conduit (60) gradually decreases and / or a second flow rate of fluid passing through the cathode (20) gradually increases. For example, the controller can first gradually open the second valve and then gradually close the first valve. The controller can also, at the same time, gradually open the second valve and close the first valve. The first valve and / or the second valve are capable of adopting at least one "intermediate" state, between the "open" state and the "closed" state.

[0080] Preferably, during the second step (190), the second valve is open and the first valve is closed. The fluid enters through the inlet conduit (40), passes through the cathode and exits through the outlet conduit (50) and the outlet of the mixer (160).

[0081] Following the second step (190), the fuel cell can be put into operation to produce electricity. In other words, following the purging process, the controller circulates hydrogen to the anode of the fuel cell in order to begin electricity production.

[0082] A purging process and the start-up of the fuel cell are described in more detail below according to the embodiment examples in Figures 1 to 3.

[0083] Figures 4, 5, 6, 7, and 8 show a mass flow rate (M) per unit time (T) as a function of elapsed time (t). These figures illustrate the purging process implemented by the fuel cell according to [Fig. 2] or 3. The fluid entering through the inlet duct (40) is preferably air, but it may be another fluid containing oxygen. To distinguish this fluid from hydrogen, it will be referred to as air.

[0084] Figure 4 shows an incoming flow into the mixer (150) from the conduit outlet (50). This is air or a mixture of air and hydrogen.

[0085] Fig. 5 shows an airflow through the bypass duct (60).

[0086] Figure 6 shows a flow rate passing through the cathode of the fuel cell. This is of a flow rate of the same fluid as that which enters through the inlet duct (40). It is therefore preferably a flow rate of air.

[0087] Figure 7 shows a flow of hydrogen passing through the cathode of the fuel cell. fuel. This refers to the hydrogen accumulated during the shutdown of the fuel cell.

[0088] Fig. 8 shows a composition of the fluid exiting through the mixer outlet (160).

[0089] Figure 1 represents a flow rate in the outlet conduit (50) at the inlet of the mixer (150).

[0090] Trace 2 represents the flow rate of a fluid mixture passing through the cathode of the fuel cell. This is a mixture of hydrogen accumulated during shutdown and the fluid entering the cathode (20) of the fuel cell.

[0091] Trace 3 represents a flow of accumulated hydrogen, exiting the cathode of the fuel cell.

[0092] Consequently, the difference between diagram 1 and diagram 2 corresponds to the flow rate circulating in the bypass duct. The difference between diagram 2 and diagram 3 corresponds to the flow rate of the fluid entering through the fluid inlet duct (40) but not passing through the bypass duct.

[0093] The purging process in the exemplary embodiment of [Fig. 1] begins at time t0. At this time t0, the fuel cell is off. Hydrogen has accumulated on the cathode side. During the off time, hydrogen has passed through the membrane (210) and accumulated on the cathode side. The hydrogen inlet (130) and outlet (140) conduits can be closed.

[0094] In a first operation, the first valve (70) is opened. Then, in a second operation, a compressor (120) is started and forces a fluid, preferably air, into the inlet duct (40).

[0095] The air entering through the inlet duct passes through the bypass duct or the cathode of the fuel cell. The air passing through the cathode mixes with the hydrogen accumulated on the cathode side and displaces the accumulated hydrogen. Then, passing through the outlet duct (50), it mixes with the air arriving through the bypass duct. The hydrogen concentration is, due to this mixing, greatly reduced. The mixture entering the mixer (150) thus has a low hydrogen concentration that presents no danger. After a given time, at time t6, the first valve (70) is closed. After t6, all the air entering through the inlet duct (40) passes through the cathode of the fuel cell.

[0096] The second valve (80) is constantly held open.

[0097] The controller then passes hydrogen through the anode of the fuel cell in order to start the fuel cell to begin electricity production.

[0098] A method for purging a fuel cell is described below according to the embodiment example of [Fig.2] or 3.

[0099] The purging process begins at time t0, shown in Figures 4 to 8. At this time t0, the fuel cell is off. There is an accumulation of hydrogen at the cathode of the fuel cell. The hydrogen inlet (130) and outlet (140) conduits can be closed.

[0100] In a first operation, the first valve (70) is open. Preferably, the second valve (80) was closed when the fuel cell was shut down and is thus in a "closed" state. Preferably, the state of the second valve is detected before the first operation, and the second valve is closed if this detection shows that it was not closed.

[0101] In a second operation, a compressor (120) is started up in order to introduce a fluid, preferably air, into the inlet duct.

[0102] The first and second operations take place between times t0 and t1. At time t1, the first valve (70) is thus in the open state. Between t1 and t2, all the air entering through the inlet duct (40) passes through the bypass duct and enters the mixer (150) from the outlet duct (50). Consequently, Figures 4 and 5 show a flow rate at the same level. [Fig. 8] shows that this flow rate does not include hydrogen. The time between times t1 and t2 corresponds to the first substep (180) during which the first valve is open, as described previously.

[0103] In a third operation, between times t2 and t3, the second valve (80) is opened. Preferably, the second valve can be opened progressively between t2 and t3. At time t3, the second valve is in an open state.

[0104] Between times t3 and t4, the airflow entering through the inlet duct (40) is divided between the bypass duct and the cathode. Figures 5 and 6 thus show a reduced flow rate through the bypass duct and an increased flow rate through the cathode. The airflow passing through the cathode mixes with the accumulated hydrogen within the cathode and pushes the hydrogen out. Figure 7 thus shows a hydrogen flow rate.

[0105] The flow entering the mixer from the outlet duct thus consists of an air-hydrogen mixture from the fuel cell cathode (areas B and C in [Fig. 8]) and air passing through the bypass duct (area A in [Fig. 8]). The hydrogen concentration in this mixture is reduced and below a threshold that does not present a danger at the mixer outlet.

[0106] Between times t4 and t5, the hydrogen accumulated in the cathode is depleted: The volume of accumulated hydrogen has been successively diluted and discharged through the mixer outlet. Consequently, the hydrogen concentration in the flow entering the mixer decreases between times t4 and t5, as shown by area C in [Fig. 8]. At time t5, the hydrogen concentration in the flow entering the mixer is close to zero.

[0107] The duration between times t3 and t5 corresponds to the hunting substep (200) as described previously.

[0108] Advantageously, the controller measures the hydrogen concentration in the outlet duct entering the mixer and compares said measured concentration with a threshold. In this case, time t5 corresponds to the moment when the hydrogen concentration in the outlet duct has fallen below said threshold.

[0109] The controller initiates a fourth operation at time t5, when the hydrogen concentration has fallen below the threshold. In this fourth operation, the first valve (70) is closed. At time t6, the first valve is thus in a closed state. Advantageously, the first valve can be closed progressively between t5 and t6. From time t6 onward, all the flow entering the inlet duct passes through the fuel cell cathode. As illustrated in [Fig. 5], no flow passes through the bypass duct after time t6. Consequently, as illustrated in Figures 7 and 8 (area B), the flow entering the mixer and exiting through the mixer outlet no longer contains accumulated hydrogen.

[0110] The duration following the time t6 corresponds to the second step (190) as described above.

[0111] In a fifth operation, at the end of the second step, the controller circulates hydrogen through the anode of the fuel cell in order to start generating electricity.

[0112] The purging process is executed by a suitable controller programmed to control the fuel cell. This computer program, executable by the controller, comprises instructions that lead the fuel cell to perform the steps described above. This program may be stored on a computer-readable medium.

Claims

Demands

1. Fuel cell (10) comprising: - a programmable controller, - an anode (30); - a cathode (20) with a fluid inlet duct (40), a fluid outlet duct (50) and a bypass duct (60) between the inlet duct and the outlet duct, - the bypass duct (60) comprising a first valve (70) controllable by the controller, - the controller being programmed to implement a cathode (20) purging process, implemented before circulating hydrogen on the anode side, the controller being programmed to: - keep the first valve (70) open during a first stage, - keep the first valve (70) closed during a second stage (190) following the first stage.

2. Fuel cell according to claim 1, wherein: the outlet conduit (50) includes a second valve (80) controllable by the controller, the bypass conduit (60) establishing a fluidic connection between - a portion of the inlet conduit and - a portion of the outlet conduit located downstream (100) of the second valve (80).

3. Fuel cell according to claim 2, wherein: the controller is programmed to keep the second valve (80) open during the second stage (190).

4. Fuel cell according to claim 2 or 3, wherein: the controller is programmed to close the second valve (80) during a first sub-step (180) of the first step.

5. Fuel cell according to claim 4, wherein: the controller is programmed to keep the first valve (70) and the second valve (80) open during a second hunting substage (200) of the first stage, between the first substage (180) and the second stage (190).

6. Fuel cell according to claim 4 or 5, wherein the controller is programmed to control the first valve (70) and the second valve (80) so that, between the end of the first sub-step (180) and the beginning of the second step (190): - a first flow of fluid circulating in the bypass conduit (60) gradually decreases and / or - a second flow of fluid passing through the cathode (20) gradually increases.

7. Fuel cell according to any one of claims 1 to 6, wherein: - the controller measures a hydrogen concentration in the outlet duct and compares the measured concentration with a threshold, - the controller is programmed to engage the second stage (190) when the measured hydrogen concentration is below said threshold.

8. Fuel cell according to any one of claims 1 to 7, wherein: the bypass duct (60) includes a calibrated vent (110) between the inlet duct and the first valve (70).

9. Fuel cell according to any one of claims 1 to 8, wherein: - the controller is programmed to circulate hydrogen on the anode side following the end of the cathode purging process (20).

10. A method for purging the cathode (20) of a fuel cell according to any one of claims 1 to 9, the purging method being carried out before circulating hydrogen on the anode side (30) and comprising the following operations: - in a first operation, opening the first valve (70); - in a second operation, starting a compressor (120) in order to introduce a fluid into the inlet conduit.

11. A method according to claim 10 wherein the fuel cell is according to claim 2, the purging method comprising an operation of closing the second valve (80) before starting the compressor (120).

12. Method according to claim 11 comprising a 3rd operation of opening the second valve (80), this opening preferably being progressive.

13. Method according to claim 12 comprising a 4th closing operation of the first valve (70), this closing preferably being progressive.

14. A method according to claim 13 comprising:

15. - in a 5th operation, a circulation of hydrogen through the anode (30) of the fuel cell. Computer program comprising program code instructions that cause the fuel cell according to claim 2 to perform the steps of the method according to any one of claims 10 to 14 when said program is executed on a computer.

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