FR2941094A1 - Electricity supplying system for motor vehicle, has supply circuit comprising set of elements that are arranged between valve and network of fluid distribution channels, and fuel gas supply circuit provided with additional storage chamber - Google Patents

Abstract

The system has an internal network of fluid distribution channels formed on an active surface of each of a stack of electrochemical cells forming a fuel cell (1) i.e. polymer electrolyte fuel cell. A supply circuit delimited by the network and a shut-off valve (110) has a set of elements that are arranged between the valve and the network. The circuit has an oxidizing gas supply circuit (12) provided at an oxidizing gas supply side, and a fuel gas supply circuit (11) that is provided at a fuel gas supply side and provided with an additional storage chamber i.e. tank (116). The shut-off valve is provided outside the fuel cell, and the network is provided inside the fuel cell.

Description

DO: YOU ARE IN THE EVENT 1 EVTIO.V

The present invention relates to fuel cells, in particular but not exclusively to electrolyte type fuel cells in the form of a polymer membrane (ie of the PEFC type for Polymer Electrolyte Fuel Cell).

STATE OF THE ART It is known that fuel cells allow the direct production of electrical energy by an electrochemical oxidation-reduction reaction from hydrogen (the fuel) and oxygen (the oxidant), without going through a conversion into mechanical energy. This technology seems promising especially for automotive applications. A fuel cell generally comprises the series combination of unitary elements, which each consist essentially of an anode and a cathode separated by a polymer membrane allowing the passage of ions from the anode to the cathode .

In general, the extinction of a battery is achieved by extending the normal electrochemical reaction of the battery until the collapse of the voltage due to the complete consumption of at least one of the residual gas. In order to limit the degradation mechanisms, in particular the corrosion of the carbon generally used as support for the PEFC stack catalyst, it must be ensured that the oxygen is depleted before the hydrogen. It must therefore be ensured that the battery is supplied with hydrogen until the end of extinction.

For safety reasons, fuel cells are usually equipped with shutoff valves in H2 and 02 that remain closed during shutdowns. In this case, it is not possible to remove the H2 from the tank during the shutdown procedure. The battery must therefore operate with only the residual hydrogen in its channels, the pipes, the internal dehumidification tanks and other elements of the supply line going from the safety valve to the fuel cell itself, these elements -2 -

being hereinafter referred to generally as the fuel cell supply circuit.

As a result of the stoichiometric relationship of the electrochemical reaction, the consumption of gas is twice as high on the hydrogen side, that is to say on the anode side. In the absence of any particular arrangement, the hydrogen is therefore normally lacking before the oxygen, especially if the natural gas volumes normally available for extinguishing in the anode and cathode supply circuits are substantially equal.

According to the patent application EP 2003719, a first solution is to guarantee the excess of hydrogen by purging the excess oxygen in the atmosphere. However, this requires that the cathode pressure is sufficiently high, which can not always be guaranteed. The object of the invention is to achieve a controlled and rapid shutdown of the fuel cell, ie to stop internal electrochemical processes so as to ensure that the volume of hydrogen at normal conditions available for the extinction is always at least twice the volume of residual oxygen under normal conditions.

BREI'E DESCRIPTION OF L'E \ 'TIOV

Continuing a different approach, it is proposed here a solution allowing to always store in the fuel cell gases in proper proportion to eliminate any risk of under-supply of hydrogen during extinguishings of the fuel cell thus limiting corrosion of the electrodes and bringing it to the right conditions for an extended stop and for a future restart.

The invention proposes an electricity supply system comprising a fuel cell and a supply of fuel gas and oxidizing gas.

fuel being formed by a stack of electrochemical cells having an anode and a cathode, each electrochemical cell having, both anode side and cathode side, an internal network of fluid distribution channels over the entire active surface of said cell, said network internal fluid distribution channels being disposed on a fluid distribution plate, the system comprising, both on the fuel gas supply side and on the oxidizing gas supply side, a supply circuit delimited by a cut-off valve on the outer side to the cell and, internally to the cell, by said internal network of fluid distribution channels, said supply circuit comprising a plurality of elements interposed between said shut-off valve and said internal network of fluid distribution channels, in which of said plurality of elements interposed between said shut-off valve and said key internal network fluid distribution channels, only the fuel gas supply duct has an additional accumulation chamber.

Thus, the invention allows an approach allowing, by a simple adaptation to calculate and implement, to ensure by the insertion of this additional accumulation chamber that the fuel gas supply circuit always has sufficient gas for the extinction of the battery results from the depletion of oxygen at the supply circuit of oxidizing gas.

This is remarkable because, in fuel cells supplied with atmospheric air to supply oxygen to the electrochemical reaction, due to the presence of nitrogen in the atmospheric air, the internal volume of the combustion gas supply circuit is very much higher than the internal volume of the fuel gas supply circuit, which does not go beyond the meaning of the rule proposed above. This is due to internal channels and pipes more widely dimensioned to convey nitrogen and the presence of a compressor in the circuit. In the end, despite a volume filled to 4/5 nitrogen, the residual H2 / O2 proportion is in general contrary to the teaching of the present invention.30 In fact, what is important for the smooth running and the good end of the extinction of a battery with corabibable, without causing damage to the electrochemical cells, it is the quantity of gas (expressed for example in moles) available for extinction. This quantity is certainly related to the volume of the circuit but it also depends on the pressure therein. Therefore, preferably, a system according to the invention is configured such that, in normal operation, the pressure in the combustion gas supply circuit and the pressure in the fuel gas supply circuit are such that than. given the internal volume of the combustion gas supply circuit and the internal volume of the fuel gas supply circuit, the number of gas fuel moles always available at the beginning of the extinguishing process in the fuel supply circuit. fuel gas is greater than or equal to twice the number of moles of residual oxygen in the combustion gas supply circuit.

In the case of fuel cells supplied with pure oxygen, the usual constructional arrangements generally do not lead to a number of moles of residual hydrogen in the fuel gas supply circuit greater than twice the number of moles of fuel. residual oxygen in the combustion gas supply circuit.

The rule of good practice set forth above, proposing the addition to the fuel gas circuit of an additional accumulation chamber, is very useful for the construction of a fuel cell allowing an efficient stopping of its operation.

In the remainder of the description, the invention is illustrated by considering an electrolyte type fuel cell in the form of a polymer membrane (that is to say of the PLFC type for Polymer Electrolyte Fuel Cell), supplied with oxygen. pure as an oxidizing gas. These two aspects are not limiting but this is a favorable embodiment for applications to transport vehicles, in particular -5

motor vehicles. Indeed, the under-supply of hydrogen is a problem to which the PEFC type fuel cells are quite sensitive.

BREI'E DEKRIPTION OF FIGURES

The remainder of the description makes it possible to fully understand all the aspects of the invention by means of the accompanying drawings in which: FIG. 1 is a diagram of an electric energy production system using a fuel cell powered in pure oxygen; Figure 2 shows a first embodiment of a specific element of the invention; Figure 3 shows a second embodiment of a specific element of the invention of the invention; FIG. 4 shows a third embodiment of a specific element of the invention of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE EMBODIMENT In FIG. 1, a fuel cell 1 of the electrolyte type is shown in the form of a polymer membrane (that is to say of the type shown in FIG. PEFC for Polymer Electrolyte Fuel Cell). The fuel cell 1 is supplied by two gases, namely the fuel (hydrogen stored or manufactured on board the vehicle) and the oxidizer (pure oxygen) which feed the electrodes of the electrochemical cells. For simplicity, Figure 1 shows only the elements of the gas circuits useful for understanding the invention.

The installation has a fuel supply circuit 11 on the anode side. A tank of pure hydrogen H2 is connected to the inlet of the anode circuit of the fuel cell 1 by means of a supply pipe which passes through a shutoff valve 110 and then by an ejector 113. A probe pressure 11 1 is installed on the pipe just before entering the fuel cell 1. Part of the fuel gas supply circuit 1 1 a recycling circuit 11R, connected to the output of the anode circuit of the battery to Fuel 1. The ejector 113 and a recirculation pump 115 ensure the recycling of unconsumed gases through a water separator 1IL- and fresh gas mixture from the tank. We also see an additional accumulation chamber 116 disposed on the piping of the fuel gas supply circuit 11, between the shutoff valve 110 and a pressure regulating valve 117. Thus, the additional accumulation chamber is in this case. preferred embodiment placed where the pressure is highest in the supply circuit.

Note that the additional accumulation chamber 116 could be disposed at any point in the fuel gas supply system, i.e. at any point between the shutoff valve 110 and the fuel cell. fuel 1, even on the recycling circuit 1 IR, or on the circuit between the water separator 114 and the ejector 113. However it is interesting to place it at a point of the circuit where the pressure is higher in order to to reduce the volume.

The installation also includes a combustion gas supply circuit 12 on the cathode side. A pure oxygen reservoir 02 is seen connected to the input of the cathode circuit of the fuel cell 1 by means of a supply pipe which passes through a shut-off valve 120 and then by a pressure regulating valve 127 , then by an ejector 123. A pressure sensor 121 is installed on the pipe just before entering the fuel cell 1. Part of the combustion gas supply circuit 11 a recycling circuit 12R, connected to the output The ejector 123 and a recirculation pump 125 recycle the unconsumed gases through a water separator 124 and the fresh gas mixture from the reservoir. Just at the gas outlet of the fuel cell 1, there is a purge vi-nne 122 for venting the oxygen circuit.30 Finally, an electric charge 14 is connected to the fuel cell 1 by an electric line 10.

It is a question of voluntarily increasing the volume of the supply circuit of the anode side by acting on the volume of the supply line going from the valve of cutoff to the fuel cell to guarantee permanently a reserve of H2 sufficient to ensure extinction without risk of under-supply of hydrogen. This part of the circuit being at a higher pressure than that of the battery, typically 12 to 15 bar. the volume needed to accumulate the amount of hydrogen needed remains moderate. 10 Let's see how to calculate the volume. Let vo be the amount of oxygen, in liter under standard conditions (ie at the temperature of 0 ° C and at the pressure of 1013 mbar), to be fully consumed during the entire extinction. . This is the residual oxygen in the cathode volume at the beginning of the extinction, minus the amount that can be purged, plus the amount that is introduced in the case of air suction as described by example in the patent application W006 / 012954.

For fuel cells using air as an oxidant, the partial pressure of oxygen must be considered for the estimation of the quantity v ,,,. Since gas consumption is twice as high on the hydrogen side. the additional volume V'd whose hydrogen feed line is increased must be calculated to ensure that: (lemdd, Ph2) + v ,. > 2 x v ,, 25 with v ,,, quoting the volume of hydrogen, in liter under standard conditions, always available at the beginning of extinction in the internal volume of the fuel gas supply system before installation of the volume additional (pipes, channels, bipolar plates, original supply line downstream of the shutoff valve 110) and Ph2 the pressure prevailing at the beginning of extinction in the part of the fuel gas supply circuit where the additional volume must be installed. This is a simplified approach 20 -8-

since it would normally be necessary to take into account the temperature of the gas and the non-linearity of the density of hydrogen as a function of the pressure, parameters a priori unknown. However it is sufficient for the desired accuracy.

The hydrogen supply pressure P112 may be substantially variable, in particular at the end of the tank. The calculation must be performed for the lowest possible hydrogen supply pressure. As a result, there may be too much hydrogen for higher pressure. If for questions of regulations or other horns. It is not desired that the cell be stored with too much residual hydrogen. In the end, it is possible to purge excess hydrogen. However it is possible to purge only if the pressure is higher than that of the atmosphere.

FIGS. 2 to 4 show different embodiments of the additional accumulation chamber 116. The additional volume that it is desired to have can be achieved for example by adding a small reservoir, in series or in parallel, to the supply line or by increasing the section and / or the length of the supply pipe for this purpose. In a practical embodiment, it is an additional accumulation chamber with an internal volume of 2 to 3 dl. The volume of the additional accumulation chamber is calculated with the formula above, placing itself in the most pessimistic scenario (minimum hydrogen pressure, minimum oxygen purge, maximum oxygen reintroduction, etc.). This is how the volume of 2dl was calculated for a cell whose cubic capacity at the anode circuit is equal to the cubic capacity of the cathode circuit and is equal to 2 liters.

In Figure 2, we see that the additional accumulation chamber takes the form of a tank 116A. This can be placed in series in a section of the supply piping. Alternatively, the tank could have only one port and could be connected to the pipe by a T-fitting. In FIG. 3, the additional accumulation chamber takes the form of an over-length of pipe 116B. In FIG. 4, the additional accumulation chamber takes the form of an enlarged diameter pipe section 116C with respect to the pipe diameter of the remainder of the supply line.

The procedure for controlling the extinction of the battery is not part of the present invention. Let us simply mention that the devices proposed by the present invention can be used both with a quenching procedure such as that described in the patent application WO06 / 012954 (see comments above), and with a quenching procedure such as that described in patent application EP 2017916, where 1G the gas pressure tends to that of water vapor, the amount of residual hydrogen can be calculated in advance to be able to purge if necessary before the pressure does not fall below the threshold of atmospheric pressure. Another solution is to use a vacuum pump to lower the amount of residual hydrogen below the desired threshold. 15

Claims (7)

REVENDICATIONS1. An electricity supply system comprising a fuel cell (1) and a supply of fuel gas and oxidizing gas, the fuel cell being formed by a stack of electrochemical cells having an anode and a cathode, each electrochemical cell comprising, at both anode side and cathode side, an internal network of fluid distribution channels over the entire active surface of said cell, said internal network of fluid distribution channels being disposed on a fluid distribution plate, the system comprising, at both on the fuel gas supply side and on the oxidizing gas supply side, a supply circuit (11, 12) delimited by a shut-off valve on the outside of the battery and, on the inside of the battery, by said internal network of fuel channels. distribution of the fluid, said supply circuit comprising a plurality of elements interposed between said shutoff valve and said internal network d e fluid distribution channels, characterized in that, among said plurality of elements interposed between said shut-off valve and said internal network of fluid distribution channels, only the fuel gas supply circuit comprises an accumulation chamber additional (116). 2. Electricity supply system according to claim 1, wherein in normal operation the pressure in the fuel gas supply circuit (pO2) and the pressure in the fuel gas supply circuit. (pH2) are such that, given the internal volume (voa) of the combustion gas supply circuit (12) and the internal volume (v ,,,) of the fuel gas supply circuit (1l), the number fuel gas moles always available at the start of the extinguishing process in the fuel gas supply circuit is greater than or equal to twice the number of moles of residual oxygen in the combustion gas supply circuit. 3. Electricity supply system according to one of claims 1 or 2, wherein the battery is supplied with pure oxygen as an oxidizing gas. An electricity supply system according to one of claims 1 to 3, wherein the fuel cell is of the electrolyte type in the form of a polymer membrane. 5. Electricity supply system according to one of claims 1 to 4, wherein the additional accumulation chamber is a reservoir (116A). An electricity supply system according to one of claims 1 to 4, wherein the additional accumulation channel is formed by an over-length of pipe (116B). 15 Electricity supply system according to one of claims 1 to 4, wherein the additional accumulation chamber is formed by a section of expanded diameter pipe (116C) with respect to the pipe diameter of the rest of the line. power. 10