Patent Application
20120325677
The invention concerns an electrochemistry method to produce a reaction gas of a lesser molar mass than that of the initial constituent(s) in the form of gas or vapour, according to which the gas or vapour of the initial constituent(s) is made to flow, and the reaction gas is recovered in the path in which the initial constituent(s) is/are made to flow.
It relates to the improvement of the efficiency of such a method.
The principal application with which the invention is concerned is electrolysis of water at high temperature (EHT), also called high-temperature steam electrolysis (EVHT).
An electrochemical reactor includes multiple elementary cells formed by a cathode and an anode separated by an electrolyte, where the elementary cells are electrically connected in series by means of interconnecting plates which are generally interposed between an anode of an elementary cell and a cathode of the next elementary cell. An anode-anode connection followed by a cathode-cathode connection is also possible. The interconnecting plates are electronic conducting components formed by one or more metal plate(s). These plates also provide the separation between the cathodic fluid flowing in one elementary cell from the anodic fluid flowing in a following elementary cell.
The anode and the cathode are made of a porous material through which the gases can flow.
In the case of electrolysis of water to produce hydrogen at high temperatures, steam flows in the cathode where the hydrogen is generated in gaseous form, and a draining gas can flow in the anode, and by this means collect the oxygen generated in gaseous form at the anode. Most high-temperature electrolysers use air as the draining gas in the anode.
At the current time the fluid circuits produced by the compartments delimited by the interconnecting plates have a relatively simple architecture.
As a general rule the fluid at the outlet of the cathode includes not only hydrogen which it is sought to produce, but also surplus steam left over from the electrolysis electrochemical reaction itself. In other words, the conversion rates of high-temperature electrolysers are not 100%. Indeed, to favour an average production density, steam is usually deliberately produced in excess quantities, which occurs to the detriment of the attaining of a high rate of steam consumption (or high hydrogen conversion rate).
After this, when it is desired to come close to a 100% conversion of steam into hydrogen, it has hitherto appeared necessary either to oversize the surface of the cells, or to optimise the distribution of the fluids over the surface such that, whatever the path followed by the steam from its inlet, the passage time is roughly the same. A disadvantage of the first option is a reduction of average production, whereas a disadvantage of the second option is an implementation (the steam circuit which must be manufactured) which may be complex.
In addition, many designers of EHT electrolysers tend, from the design stage, to pay particular attention to the level of density of production to be attained, to the detriment, therefore, of the conversion rate, as set out above.
Lastly, in respect of these same designers, it is easy at the outlet of the cathode to separate the unconverted steam from the hydrogen produced by, for example, installing additional means downstream and outside the high-temperature electrolyser, where the function of these additional means is to separate the remaining steam from the hydrogen produced. In most designs of electrolysers which are currently manufactured these additional means are constituted by condensers fitted outside the electrolysers to separate the water from the hydrogen. Selective porous membranes have also been mentioned as additional means, also fitted outside the electrolysers, which allow the hydrogen to pass through preferentially, compared to the steam.
The disadvantages of high-temperature electrolysers according to the state of the art, as described above, can therefore be summarised as follows: their efficiency is not perfect due to the fact that steam remains at the outlet, and their operation requires the use of additional downstream means to separate the hydrogen produced from the steam left over from the electrolysis reaction itself.
One aim of the invention is therefore to compensate for all or some of the disadvantages of the prior art, and therefore to propose a solution which at least enables the hydrogen production efficiency to be improved in a high-temperature electrolyser.
A more general aim of the invention is to propose a solution which enables the efficiency of an electrochemistry method to be improved with a view to producing a reaction gas of lesser molar mass than that of the initial constituent(s) in the form of gas or vapour, according to which the gas or vapour of the initial constituent(s) is made to flow, and the reaction gas is recovered in the path in which the initial constituent(s) is/are made to flow.
To accomplish this, one aim of the invention is an electrochemistry method to produce a reaction gas of lesser molar mass than that of the initial constituent(s) in the form of gas or vapour, according to which the gas or vapour of the initial constituent(s) is/are made to flow, and the reaction gas is recovered in the path in which the initial constituent(s) is/are made to flow, characterised in that at least one vortex is created in a zone upstream from the reaction gas recovery zone, where the vortex is able to separate the produced reaction gas from the initial constituent(s) which is/are still present, in order to subject the latter to an electrochemical process in the said upstream zone.
It is self-evident that a zone upstream from the reaction gas recovery zone must be considered in the broad sense as being a reaction zone in which the transformation from steam to hydrogen takes place.
Thus, the invention essentially consists in slowing the output of the initial constituent(s) compared to the gas derived from the reaction which, since it is less dense, will be able to be output directly, whereas the initial constituent(s) will be ejected tangentially towards the outside of the vortex, and therefore be subjected once again to an electrochemical process in the zone upstream from the outlet.
From one standpoint the invention relates to a method of high-temperature electrolysis of water according to the method described above, and implemented by at least one elementary electrolysis cell formed of a cathode, an anode and an electrolyte inserted between the cathode and the anode, according to which steam at least, in contact with the cathode, is made to flow from an inlet end to an outlet end, through which end the produced hydrogen is recovered, and according to which at least one vortex is created in a zone upstream from the outlet end, where the vortex/vortices is/are able to separate the produced hydrogen from the steam which is still present in order to subject the latter to an electrolytic process in the said upstream zone.
According to the invention, means to create a vortex are therefore incorporated into the high-temperature electrolyser itself, which therefore favour the output of the hydrogen, and which slow the output of the steam by ejection to outside the vortex.
The creation of a vortex (or swirl) enables high centripetal accelerations to be attained, and therefore centrifugal forces to be exerted, of different intensities depending on the species. The term “high temperatures” is understood to mean, in the context of the invention, temperatures at least equal to 450° C., and typically of between 700° C. and 1000° C.
Due to this integration it is possible to envisage manufacturing a high-temperature electrolyser (EHT) with an inlet for steam and a single outlet for the produced hydrogen, since the surplus steam in the vicinity of the outlet is once again transformed into hydrogen. An electrochemical reactor for electrolysis of water thus completely transforms the steam provided at the inlet, provided that the steam remains for a sufficiently long time. Therefore, by creating one or more vortices, the water molecules will be kept for a longer period in the active electrochemical reaction zone by centrifugation; and they will have an increased possibility of being transformed into hydrogen.
The electrolysis of water concerned by the invention is preferably accomplished at temperatures of between 700° C. and 1000° C.
Advantageously, in order to improve performance, i.e. the electrochemical efficiency, multiple vortices in parallel or in series relative to one another are created in the zone upstream from the outlet end.
Each vortex is preferably created with a tangential speed at least equal to 80 m/s, and preferably greater than 100 m/s.
Also preferably, each vortex is created such that it is possible to obtain an acceleration of greater than 106m/s2.
The invention also concerns an electrochemical reactor, intended to produce a reaction gas of lesser molar mass than that of the initial constituent(s) in the form of gas or vapour, including a stack of elementary electrochemical cells, each formed from a cathode, an anode and an electrolyte inserted between the cathode and the anode, where at least one interconnecting plate is fitted between two adjacent elementary cells and in electrical contact with one electrode of one of the two elementary cells and one electrode of the other of the two elementary cells, where the interconnecting plate delimits at least one cathodic compartment and at least one anodic compartment for the flow of fluids respectively at the cathode and at the anode, characterised in that it includes means to create at least one vortex in a zone upstream from the outlet end of the cathodic compartments and/or of the anodic compartment, where the vortex/vortices is/are able to separate the produced reaction gas from the initial constituent(s) which is/are still present, in order to subject the latter to an electrochemical process in said upstream zone.
The means to create the vortex/vortices advantageously consist of holes pierced in the at least one interconnecting plate upstream from the outlet end of the cathodic compartments. This solution is simple to implement and can be applied easily in all types of interconnecting plates.
With the habitual flow rates found in an EHT electrolyser and the dimensions of the cells of electrolysers, the diameter of the holes is preferably less than 1 mm.
Lastly, the invention concerns a plate, intended to be used as an interconnecting plate in a reactor as described above, consisting of an assembly of two partially buckled plates forming dished recesses in the form of grooves, where the assembly includes at least one aperture, each of which traverses both assembled metal plates, and made in a differently dished zone at the end of the grooves, and holes traversing a single one of both metal plates, also made in the differently dished zone at the end of the grooves, and where the holes are distributed on the periphery of the aperture; where the diameter of the holes is of the order of 1 mm or less, and the assembly of both metal plates in the differently dished zone delimits a passage between the two metal plates, and between the holes and the aperture on the periphery of which they are made.
There is preferably an even number of holes. By this means alternate rotation of the vortices is favoured.
Again preferably, the end of the grooves are made such that a gas jet or blend of gas and vapour is created in the said end, where the jet also has an outflow tangential to one of the holes. The vortices phenomenon is favoured by bringing about the jet tangentially in this manner.
Other characteristics and advantages will be seen more clearly on reading the detailed description made with reference to the figures, among which:
The invention is described in relation to a type of architecture of high-temperature water electrolyser to generate hydrogen. It is self-evident that the invention can be applied to other architectures, and also to other chemical or electrochemical reactors, in which there is, firstly, a reaction product which is less dense than the initial product(s), where the transformation reaction requires time “and reconcentration”, and where the device can be inserted into it. The high temperatures at which the represented electrolyser operates are between 700° C. and 1000° C.
It is stipulated that the terms “upstream” and “downstream” are used with reference to the direction of flow of the steam and of the hydrogen produced at the cathode.
It is stipulated that the representations of the different elements are not to scale.
In
Each elementary cell includes an electrolyte positioned between a cathode and an anode.
In the remainder of the description we shall describe cells C1 and C2 and their interface in detail.
Cell C1 includes a cathode 2.1 and an anode 4.1 between which is positioned an electrolyte 6.1, for example a solid electrolyte, generally 100 μm thick in the case of cells called “electrolyte support” cells and several μm thick in the case of cells called “cathode support” cells.
Cell C2 includes a cathode 2.2 and an anode 4.2 between which an electrolyte 6.2 is positioned. All the electrolytes are of the solid type.
Cathodes 2.1, 2.2 and anodes 4.1, 4.2 are made of a porous material and are, for example, more than 500 μm thick, typically the order of 1 mm and 40 μm respectively.
Anode 4.1 of cell C1 is connected electrically to cathode 2.2 of cell C2 by an interconnecting plate 8 which comes into contact with anode 4.1 and cathode 2.2. In addition, it allows anode 4.1 and cathode 2.2 to be powered electrically.
An interconnecting plate 8 is interposed between two elementary cells C1, C2.
In the represented example it is interposed between an anode of an elementary cell and the cathode of the adjacent cell. But it could be interposed between two anodes or two cathodes.
Interconnecting plate 8 defines, with the adjacent anode and adjacent cathode, channels through which fluids flow. More specifically, they define anodic compartments 9 dedicated to the flow of the gases in anode 4 and cathodic compartments 11 dedicated to the flow of the gases in cathode 2.
In the represented example an anodic compartment 9 is separated from a cathodic compartment 11 by a wall 9.11. In the represented example, interconnecting plate 8 also includes at least one duct delimiting, with wall 9.11, anodic compartments 9 and cathodic compartments 11.
In the represented example the interconnecting plate includes multiple ducts 10 and multiple anodic compartments 9 and cathodic compartments 11. Advantageously, duct 10 and the compartments have hexagonal honeycomb sections, which enables the density of compartments 9, 11 and ducts 10 to be increased.
As represented in
Arrows 12 of
As represented in
It may be decided to cause a draining gas to flow in anodic compartments 9 to evacuate the oxygen (see arrows 13). Arrows 12 and 13 of
The inventor found that at the outlet end of each cathode steam blended with the produced hydrogen remained: this steam is therefore left over from the electrolysis reactions which took place upstream.
It is known to treat this surplus steam by separating it from the produced hydrogen, most often by means of condensers fitted downstream from the electrolyser.
The inventor then had the idea of creating one or more vortex/vortices upstream from the outlet, i.e. upstream from the outlet aperture dedicated to collecting the produced hydrogen.
Indeed, the relative density between the steam and the produced hydrogen in the blend arriving close to the outlet of each elementary electrolysis cell is equal to 9 since the molar mass of hydrogen is equal to 2 g·mol−1, whereas that of steam is equal to 18 g·mol−1.
Therefore, by creating one or more vortex/vortices in the flow stream of the blend constituted by the produced hydrogen and the surplus steam, both types of molecules (H2 and H2O) are subjected to a differentiated centrifugal force, which amounts to favouring the centrifugation of the heavy molecules (H2O) and the extraction of the light molecules (H2).
This phenomenon of ejection of the steam molecules at the outlet is more intense the closer it occurs to the outlet.
In
Each interconnecting plate 8 consists of an assembly of two metal plates 8.1, 8.2 which have been partially buckled, forming dished recesses in the form of grooves 80.
As represented in
This aperture 84 is made in a zone Z which is dished in a different manner to the recesses, at the end of grooves 80. This zone Z which is dished in a different manner to the recesses can be non-dished.
In zone Z which is dished in a different manner at the end of grooves 80, holes 83 traverse a single one of the two metal plates 8.1, and are regularly distributed on the periphery of aperture 84.
The diameter of holes 83 is of the order of 1 mm, but it may be less. There is preferably an even number of holes 83, so as to favour alternate rotation of the vortices. Thus, as represented in
The assembly of the two metal plates 8.1, 8.2 in differently dished zone Z delimits a passage 840 between the two metal plates 8.1, 8.2 and between holes 83 and aperture 84 (
Grooves 80 are the grooves dedicated to the collection of the produced hydrogen. Similarly, aperture 84 is the aperture dedicated to the recovery of the hydrogen produced by the electrolysis reaction: it habitually constitutes a portion of a collection assembly called a supply manifold, and in which a pierced pipe (unrepresented) is installed.
Due to the presence of holes 83 of diameter less than or equal to 1 mm, and to the flow rate at the inlet to zone Z, the blend (surplus steam and produced hydrogen) which arrives in this zone Z passes through several vortices in parallel with tangential speeds of over 100 m/s.
The blend is therefore subject to an acceleration which is calculated using the following formula:
Or
i.e. an acceleration close to 1 million times terrestrial acceleration.
With such an acceleration the lighter hydrogen molecules tend to be evacuated through holes 83 which are in fluid communication with recovery aperture 84 (see arrow 15 in
As represented in
It is clear that due to the invention curve 5 is closer than curve 3 to theoretical straight line LT. In other words, the creation of vortices according to the invention causes a movement towards to a steam conversion rate of close to 100%.
The invention described above therefore consists in creating one or more vortex/vortices in a zone upstream from the recovery zone, i.e. one or more vortex/vortices tangentially to the axis of the holes for recovery of the gases produced from the electrochemical reaction, by slowing the evacuation of the reaction gas (H2 in the example), and by tending to subject the gas or vapour which constitutes the initial constituent(s) to another electrochemical process.
It is stipulated that, compared to the various methods of creation of vortices in the state of the art used to separate two constituents, in this case there is a single inlet of gas/vapour and a single outlet of gas, and the vortex/vortices is/are created tangentially to the axis of the reaction gas recovery hole. And, unlike the vortices created according to the state of the art, in which the lightest molecules are rejected towards the outside, in the invention vortices are created to eject the heaviest molecules, i.e. those of the initial constituent(s), to the outside.
The invention described above has many advantages.
Indeed, by incorporating vortex-creation means directly within an elementary electrolysis cell itself, the advantages are as follows:
Although described with reference to a high-temperature electrolyser, the solution according to the invention is applicable to all electrochemistry methods in which the reaction gas has a lesser molar mass than the initial constituent(s) in a vapour or gas form, provided the vortex/vortices according to the invention enable(s) the heaviest molecules to be separated by centrifugation from the initial constituent(s) of the reaction gas. The initial constituent(s) are thus subject once again to the electrochemical reaction in the upstream zone in immediate proximity to the outlet from which the reaction gas is recovered.
For example, in a fuel cell of the PEMFC type, the reaction which occurs at the cathode is written as follows:
O2+4H++4e−→2H2O.
By creating vortices in accordance with the invention at the cathode outlet it is conceivable to evacuate the steam produced more easily than the supplied oxygen.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 51786 | Mar 2010 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/053724 | 3/11/2011 | WO | 00 | 9/12/2012 |
