# Patent

## Title
Method and installation for blowing out water in a fuel cell hydrogen circuit

## Abstract

The installation comprises cells which are comprised each of two anode compartments (41 and 42), a connection between the outlet (91) of the first anode compartment and the inlet (82) of the second anode compartment, a connection between the outlet (92) of the second anode compartment and the inlet (81) of the first anode compartment, a circuit (10) for supplying hydrogen to the anode circuits of the cells by two branches in parallel (111 and 112) controlled by two opening-closing members (121 and 122), elements periodically control the reversal of the condition of the members.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This is the 35 USC 371 national stage of international application PCT/FR01/03360 filed on 29 Oct. 2001, which designated the United States of America.
FIELD OF THE INVENTION
The present invention relates to the technical field of fuel cells and relates more particularly to cells of the type using, as combustion supporter, air enriched or not in oxygen, or even pure oxygen and, as fuel, hydrogen.
The structures of fuel cells of the above type are known as well as their principle of operation which involves the consumption of hydrogen in the anode compartment.
BACKGROUND OF THE INVENTION
Such operation is characterized by the production in the anode circuit of water, nitrogen diffusing through the membrane separating the anode compartment from the cathode compartment, as well as possibly impurities initially present in the hydrogen and which tend to concentrate.
So as to maintain optimum operating conditions, water, nitrogen and impurities are eliminated by proceeding generally to regular purges of the hydrogen circuit.
The frequency of the necessary purges depends on the characteristics of the cell as well as the operating cycles and can range from several seconds to several minutes.
One of the operating characteristic of such cells is also to leave, at the outlet of the anode circuit, a residual quantity of unconsumed hydrogen which is thus lost if the elimination of water, nitrogen and impurities is carried out by periodic purges.
So as to avoid a loss of hydrogen, the prior art ensured a recirculation of the mixture from the outlet of the anode compartment to reinject it at the inlet of the same compartment of the cell. Such a reinjection ensures continued mixing of the gases and improves the operation in the presence of impurities and nitrogen but however does not solve the problem of recovery of the water which is to be recovered so as to promote the hydraulic balance of the operation, particularly to ensure moistening and/or cooling of the cells.
The choice of proceeding with recirculation of the mixture requires using particular technical means and, particularly, the presence of a circulator which constitutes a rotary machine that is relatively complicated and subject to sensitive operating conditions, particularly in the presence of liquid water.
Such a rotary machine constitutes costly equipment, requiring substantial maintenance and, as a result, substantially increasing the purchase price as well as the operating cost of a fuel cell.
Moreover, it has been noted that the recirculation of mixture does not always improve the conditions effective to eliminate water, particularly when the speed of the principal gaseous mixture is not sufficient. This drawback could be overcome at least in part by subjecting the mixture to more rapid recirculation, but then the problems inherent in the presence of the circulator proportionately increase.
No matter what the operational conditions described above, it is moreover always necessary to have a particularly effective phase separator so as to be able to ensure the separation of the water. However, such a separator constitutes a relatively burdensome accessory, occupying a substantial volume and giving rise to problems of inertia in the case of stopping or starting the operation of a fuel cell.
SUMMARY OF THE INVENTION
The present invention relates to a process and installation seeking to eliminate the above drawbacks by using a technical means of small size, low cost, low maintenance and which are adapted to bring about, by alternate circulation, a purge of the water included in the hydrogen circuit of a fuel cell.
To achieve the above object, the purge process, according to the invention, is characterized in that it consists in:

    
    
        making each cell so as to comprise a pair of first and second anode compartments,
        connecting the outlet of the first anode compartment to the inlet of the anode circuit of the second anode compartment,
        connecting the outlet of the second anode compartment to the inlet of the first anode compartment,
        connecting the inlets of the anode circuits of the cells with a hydrogen supply circuit through two parallel branches controlled by two opening-closing members,
        periodically controlling the reversal of the conditions of said members.
    
    


The invention also has for its object an installation for the practice of the above process, such an installation being characterized in that it comprises

    
    
        cells which are each comprised of a pair of first and second anode compartments,
        a connection between the outlet of the first anode compartment and the inlet of the second anode compartment,
        a connection between the outlet of the second anode compartment and the inlet of the first anode compartment,
        a hydrogen supply circuit for the anode circuits of the cells by means of two parallel branches and controlled by two opening-closing members,
        means to control periodically the reversal of the conditions of said members.
    
    





BRIEF DESCRIPTION OF THE DRAWINGS
The various other characteristics will become apparent from the description given below with reference to the accompanying drawings which show, by way of non-limiting example, embodiments of the structure and method of the invention.
FIG. 1 is a schematic view showing the invention in a simplified embodiment of a fuel cell.
FIG. 2 is a schematic view relating to a fuel cell embodiment comprised by n cells, but depicting only the hydrogen IN/OUT circuits.
FIG. 3 is a schematic view analogous to FIG. 1 but showing one phase of the process.
FIGS. 4 and 5 are schematic views analogous to FIGS. 1 and 3, but corresponding to a modified embodiment of the invention.



DETAILED DESCRIPTION OF THE INVENTION
In the simplified embodiment shown in FIG. 1, a fuel cell designated by 1 comprises a cell 2 which is constituted by two half-cells 21 and 22 having the same constituent characteristics. Each half-cell comprises a cathode compartment 31, 32 and an anode compartment 41, 42 each containing a cathode electrode and an anode electrode which are separated by a permeation and reaction membrane 51, 52.
In a conventional manner, the compartments 31 and 32 are connected to a circuit 6 for the supply of an oxidizer such as pure oxygen or air enriched or not in oxygen. Also conventionally, the anode compartments 41 and 42 are connected to a supply circuit for fuel, which is to say hydrogen, which, according to the invention, gives rise to the following structural arrangements.
The hydrogen supply circuit of the half-cell 21 is designated by reference 71 and comprises an inlet 81 and an outlet 91, whilst the corresponding circuit for the half-cell 22 comprises an inlet 82 and an outlet 92.
According to the invention, the outlet 92 of the cell 22 is connected to the inlet 81 of the compartment 41 of the first half-cell. Similarly, the outlet 91 of the compartment 41 is connected to the inlet 82 of the compartment 42 of the second half-cell 22.
The circuits 71 and 72 are moreover connected to a circuit 10 for supplying hydrogen by means of two branches 111 and 112 in parallel and which are controlled by two opening-closing members 121 and 122.
Preferably, but not necessarily, the members 121 and 122 are of the all or nothing type by being reversely conjugated and are controlled to reverse their conditions in a synchronous manner by suitable technical means, such as particularly a timer.
The means which are described with respect to the cell 2 are transposable, with the necessary changes having been made, to a fuel cell 1 comprised of n cells 2 as per FIG. 1, such as cells 2′, 2′′ . . . 2′′′′, shown in FIG. 2, where only the hydrogen circuits connected to the anode compartments of the cells are depicted.
In such a case, the inlets and outlets of the different cells 2 are connected by collectors 13, 14, 15 and 16, whilst the circuit portions 71 and 72 are connected to the common supply 10 by means of two parallel branches 111 and 112. It must be considered that the equivalent means can be used to assume the same function and that, in certain cases, it is possible to envisage the use of a circuit supplying the two branches and the two members 12 for each cell 2.
In service, as shown in FIG. 1, the member 121 is open whilst the member 122 is closed. As a result, hydrogen under the pressure of the supply circuit 10 flows through branch 111, passes through the open member 121 and enters the circuit 71 to supply hydrogen to the anode compartment 41.
The operative reaction takes place in the usual way in the half-cell 21 whose cathode compartment is supplied with oxidizer.
During this operating phase, the essentially gaseous mixture which leaves the anode compartment 41 flows through the outlet 91 to follow the circuit 72 and to be recycled into the anode compartment 42 of the half-cell 22 whose cathode compartment 32 is also supplied with oxidizer.
The residual hydrogen which is thus recycled is consumed in the half-cell 22 whose compartment 42 is subject, despite non-optimum operating conditions, to mixing or circulation of the gaseous mixture by the recycling of the latter from the outlet of the anode compartment 41.
After an operating phase characterized by timing of a predetermined duration which may be adjustable, the condition of the members 121 and 122 is reversed as shown in FIG. 3 such that hydrogen is then supplied to the anode compartment 42 whose outlet 92 ensures recycling toward the inlet of compartment 41 of the half-cell 21, of the mixture of gas from the reaction taking place within the half-cell 22.
The same advantages are thus obtained and permit ensuring, under the best conditions, the separation of the included water by interposing, for example at the outlet 91 or 92, or even beyond these two outlets, at least two and preferably two separators 14 having an outlet 15 for the elimination of water.
It must be considered that the members 121 and 122 can be constituted by valves or similar devices and that they can also be replaced by flap valves or other members sensitive to pressure, if desired associated with non-return technical means.
In such a case, the pressure variations which take place as a function of the cyclic supply of one half-cell, and then the other one, permit, as a function of the threshold of adjustment imposed on the members 121 and 122, an automatic reversal of their condition, either by separate control or by conjoint control.
There can also be used, to ensure the same function, detectors of the partial pressure of hydrogen 17 controlling the change of condition of the members 121 and 122.
FIGS. 4 and 5 show a modified embodiment in which the outlets 91 and 92 are controlled by members 181 and 182, such as valves, which are controlled reversely in direct relation to the members 121 and 122, by being subjected to analogous conditions of operation. The valves 181 and 182 can also be of the automatic sequence type or, on the contrary, under timed control or under the control of the detection of pressure thresholds, particularly by detectors 17. In such an arrangement, when the supply of the anode compartment 41 is ensured by opening the member 121, the valve 18 is then preferably closed, whilst the valve 181 can be optionally open or closed.
During reversal of supply, the member 121 is closed whilst the member 122 is open and, simultaneously, the valve 181 is closed as shown in FIG. 5.
FIG. 4 shows that at least one separator 17 can be disposed between the outlet 92 and the valve 182 or between the outlet 91 and the valve 181.
It should be considered that a separator 17 can also be disposed downstream of each of the valves 181, 182.
The invention is not limited to the examples described and shown, because various modifications can be given to it without departing from its scope.

## Claims

1. A fuel system comprising:
at least a pair of a first cell and a second cell, each cell having an anode compartment with an inlet and an outlet and a cathode compartment with an inlet and an outlet;
a hydrogen circuit comprising:
a first distinct loop interconnecting the outlet of the anode compartment of the second cell to the inlet of the anode compartment of the first cell without any connection to any inlet of the second cell,
a second distinct loop interconnecting the outlet of the anode compartment of the first cell to the inlet of the anode compartment of the second cell without any connection to any inlet of the first cell,
a supply line selectively connectable to the first and second loops through first and second valve means

and control means for alternatively operating said first and second valve means.

2. The system of claim 1, wherein said control means include timing means.

3. The system of claim 1, wherein said control means include pressure sensing means.

4. The system of claim 1, wherein said control means include hydrogen partial pressure measuring means.

5. The system of claim 1, wherein said first and second loop each include a valve downstream of the respective anode outlet, operable under control of said control means.

6. The system of claim 5, wherein said control means operate to alternatively actuate said valves in said first and second loops.

7. The system of claim 1, wherein said first and second loops each include a water separator.