WO2011110675A1 - Electrochemical process having improved efficiency and related electrochemical reactor such as a high temperature electrolyzer (hte) - Google Patents

Abstract

The invention relates to a novel electrochemical process with a view to producing a reaction gas having a molar mass lower than that of the starting component(s) in the form of a gas or vapor, according to which the gas or vapor of the starting component(s) is circulated and the reaction gas is recovered in the circulation path of the starting component(s). According to the invention, a least one vortex is created in a zone upstream of the reaction gas recovery zone, the vortex being capable of separating the product reaction gas from the starting component(s) still present in order to subject the latter to an electrochemical process in said upstream zone. The invention can be used for the electrolysis of water at high temperatures according to which the hydrogen produced is separated from the surplus water vapor using the vortex in order to subject the latter to electrolysis within the electrolyzer.

Description

 IMPROVED YIELD ELECTROCHEMISTRY PROCESS AND ELECTROCHEMICAL REACTOR SUCH AS ELECTROLYSURER

 HIGH TEMPERATURE (EHT) ASSOCIATED

DESCRIPTION

TECHNICAL AREA

The invention relates to an electrochemical process for producing a lower molar mass reaction gas than that of the initial constituent (s) (ux) in the form of gas or vapor, according to which the gas or vapor of the initial constituent (s) (ux) and the reaction gas is recovered in the flow path of the initial constituent (s) (ux).

 It relates to improving the efficiency of such a process.

 The main application targeted by the invention is the electrolysis of high temperature water (EHT) also called electrolysis of high temperature water vapor (EVHT).

PRIOR ART

An electrochemical reactor comprises a plurality of elementary cells formed by a cathode and an anode separated by an electrolyte, the elementary cells being connected electrically in series by means of interposed interconnecting plates, generally between an anode of an elementary cell and a cathode of the next elementary cell. Anode-anode connection followed by cathode-cathode connection is also possible. Interconnecting plates are electronic conductive components formed by one or more metal plates. These plates also ensure the separation between the cathodic fluid circulating at the level of an elementary cell of the anode fluid flowing in a next elementary cell.

 The anode and the cathode are porous material in which the gases can flow.

 In the case of the electrolysis of water to produce hydrogen at high temperatures, water vapor circulates at the cathode where hydrogen is generated in gaseous form, and a draining gas can circulate at the same time. level of the anode and thus collects oxygen generated in gaseous form at the anode. Most high temperature electrolysers use air as the draining gas at the anode.

 To date, the fluid circuits made by the compartments delimited by the interconnecting plates have a relatively simple architecture.

In general, the fluid at the outlet to the cathode comprises not only the hydrogen gas that is to be produced, but also the excess water vapor with respect to the electrochemical reaction of electrolysis itself. In other words, conversion rates of electrolysers at high temperatures are not 100%. Indeed, to promote a medium density of production, it is usually carried out voluntary overeating water vapor, which is to the detriment reaching a high rate of water vapor utilization (or hydrogen conversion rate).

 Then, when it is desired to approach the 100% conversion of water vapor into hydrogen, it appears necessary until now either to oversize the surface of the cells, or to optimize the distribution of fluids on the surface in such a way regardless of the path followed by the water vapor since its entry, the travel time is substantially the same. The first option has the disadvantage of a decrease in average production, while the second option has the disadvantage of an implementation (water vapor circuit to be realized) which can be complex.

 In addition, many EHT electrolyser designers tend to favor the level of production density to be achieved as early as the design phase and therefore at the expense of the conversion rate as stated above.

Finally, for these same designers, it is easy at the cathode outlet to separate the unconverted water vapor from the hydrogen produced, for example by implanting additional means downstream and outside the electrolyser. high temperatures, the function of these additional means being to separate the remaining water vapor of the hydrogen gas produced. In most electrolyser designs provided to date, these additional means consist of condensers arranged outside the electrolysers to separate water from hydrogen. It has also been mentioned as additional means, selective porous membranes also arranged outside the electrolysers which preferentially pass hydrogen over water vapor.

 So we can summarize to date the disadvantages of electrolysers at high temperatures according to the state of the art as described above: their performance is not perfect because there is still water vapor output and their operation requires the use of additional downstream means for separating the hydrogen gas produced from the excess steam of the actual electrolysis reaction.

 An object of the invention is therefore to overcome all or part of the disadvantages of the prior art and therefore to provide a solution that at least improve the production efficiency of hydrogen in a high temperature electrolyzer.

A more general object of the invention is to propose a solution which makes it possible to improve the yield of an electrochemical process with a view to producing a reaction gas with a molar mass lower than that of the initial constituent (s) (ux). ) in the form of gas or vapor, according to which the gas or vapor of the initial constituent (s) (ux) is circulated and the reaction gas is recovered in the circulation path of the constituent (s) ) initial (ux). STATEMENT OF THE INVENTION

To do this, the subject of the invention is an electrochemical process for producing a reaction gas of molar mass lower than that of the initial constituent (s) (ux) in the form of gas or vapor, according to which the gas or vapor of the initial constituent (s) (ux) is circulated and the reaction gas is recovered in the circulation path of the initial constituent (s) (ux), characterized in that at least one vortex is created in an area upstream of the reaction gas recovery zone, the vortex being capable of separating the reaction gas produced from the initial constituent (s) (ux) still present ( s) in order to subject the latter (s) electrochemistry in said upstream zone.

 It goes without saying that an area upstream of the reaction gas recovery zone is to be considered in the broad sense as being a reaction zone in which the transformation of water vapor into hydrogen takes place.

 Thus, the invention essentially consists in slowing down the exit of the initial constituent (s) (ux) with respect to the gas resulting from the reaction which is lighter and can go out directly while the initial constituent (s) (s) ( ux) is going to be ejected tangentially to the outside of the vortex and thus again undergo electrochemistry in the upstream zone of the outlet.

In one aspect, the invention relates to a method of electrolysis of water at high temperatures according to the process described above and implemented by at least one elementary electrolysis cell formed of a cathode, anode and an electrolyte interposed between the cathode and the anode, in which at least water vapor is circulated in contact with with the cathode from an inlet end to an outlet end through which the produced hydrogen is recovered, and wherein at least one vortex is created in an area upstream of the outlet end, the vortex (s) being capable of separating the hydrogen produced from the still present water vapor in order to subject the latter to electrolysis in said upstream zone.

 According to the invention, means are thus integrated within a high temperature electrolyser to create a vortex which thus promotes the exit of the hydrogen and slow the exit of the water vapor by ejection outside the vortex.

 The creation of a vortex (or vortex) allows to achieve high centripetal accelerations and thus to exercise centrifugal forces of different intensities depending on the species. By "high temperatures" it is understood in the context of the invention, temperatures of at least 450 ° C, typically between 700 ° C and 1000 ° C.

Thanks to this integration, it is possible to design a high-temperature electrolyser (EHT) with an inlet for water vapor and a single outlet for the hydrogen produced since the excess water vapor near the outlet is transforms again into hydrogen. Thus, an electrochemical reactor for electrolysis of water completely transforms the input water vapor provided that it stays long enough. Therefore, by creating one or more vortices, the water molecules will be kept longer in the active electrochemical reaction zone by centrifugation, they will have an increased possibility of turning into hydrogen.

 The electrolysis of the water targeted by the invention is preferably carried out at temperatures of between 700 ° C. and 1000 ° C.

 Advantageously, to increase the performance, ie the electrochemical efficiency, a plurality of vortices are created in parallel or in series with each other in the zone upstream of the outlet end.

 Each vortex is preferably created with a tangential velocity of at least 80 m / s, preferably greater than 100 m / s.

More preferably, each vortex is created in such a way as to obtain an acceleration greater than 10 ⁶ m / s ² .

The invention also relates to an electrochemical reactor for producing a molar mase reaction gas lower than that of the initial constituent (s) in the form of gas or vapor, comprising a stack of cells. elementary electrochemical cells each formed of a cathode, an anode and an electrolyte interposed between the cathode and the anode, at least one interconnecting plate being arranged between two adjacent elementary cells and in electrical contact with an electrode of one of the two elementary cells and an electrode of the other of the two elementary cells, the interconnecting plate delimiting at least one cathode compartment and at least one anode compartment for the circulation of fluids respectively to the cathode and the anode, characterized in that it comprises means for creating at least one vortex in an area upstream of the outlet end of the cathode compartments and / or anode compartments, the vortex (s) being able to separate the gas reaction product product of the constituent (s) initial (ux) still present (s) to make it (s) last (s) an electrochemistry in said upstream zone.

 The means for creating the vortex (s) advantageously consist of holes drilled in the at least one interconnecting plate upstream of the outlet end of the cathode compartments. This solution is simple to implement and can be easily applied in any type of interconnect plates.

 With the usual flow rates encountered in an EHT electrolyser and the dimensions of the electrolyser cells, the diameter of the holes is preferably less than 1 mm.

The invention finally relates to a plate, intended to be used as an interconnecting plate in a reactor described above, consisting of an assembly of two partially stamped sheets forming grooves in the form of grooves, the assembly comprising at least an opening through each of the two sheets assembled and made in a differently stamped end region of the grooves and holes passing through only one of the two sheets also made in the area differently stamped end of the grooves and being distributed at the periphery of the opening; the diameter of the holes being of the order of 1 mm or less and the assembly of the two sheets in the differently stamped area delimits a passage between the two sheets and between the holes and the opening on the periphery of which they are made.

 Preferably, the number of holes is even. This promotes rotation of the vortex alternately.

 More preferably, the end of the grooves is made such that a jet of gas or mixture of gas and vapor is created in said end, the jet further having a flow tangential to one of the holes. The vortex phenomenon is promoted by bringing the jet tangentially.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages will become more apparent on reading the following detailed description given with reference to the figures among which:

 FIG. 1 is a side view of an embodiment of a reactor for high temperature electrolysis according to the present invention,

FIG. 1A is a sectional view of the reactor, FIG. 1 along plane AA, FIG. 1B is a sectional view of the reactor, FIG. 1 along plane BB,

 FIG. 2 is a view from above of an interconnecting plate according to the invention used in a reactor for high temperature electrolysis,

 FIG. 2A is a detailed sectional view of FIG. 2 along the axis A-A;

 FIG. 3 is a schematic representation of the physical phenomenon according to the invention,

 FIG. 4 is a graphical representation of the evolution of the average production as a function of the inlet water vapor flow rate, of an EHT electrolyser according to the state of the art and according to the invention respectively. DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The invention is described in connection with a type of high temperature water electrolyser architecture to produce hydrogen. It goes without saying that the invention can be applied to other architectures as well as to other chemical or electrochemical reactors in which there is on the one hand a reaction product lighter than the initial product or products, that the transformation reaction requires time "and reconcentration" and that the device can be inserted therein. The high temperatures at which the illustrated electrolyser operates are between 700 ° C and 1000 ° C.

It is specified that the terms "upstream" and "downstream" are used by reference with the meaning of circulation of water vapor and hydrogen produced at the cathode.

 It is specified that the representations of the different elements are not to scale.

 In Figure 1, there is shown an EHT electrolyser according to the present invention comprising a plurality of elementary cells C1, C2 ... stacked.

 Each elementary cell comprises an electrolyte disposed between a cathode and an anode.

 In the remainder of the description, we will describe in detail the cells C1 and C2 and their interface.

 The cell C1 comprises a cathode 2.1 and an anode 4.1 between which is disposed an electrolyte 6.1, for example a solid generally of thickness 100 μιη for the so-called cells with electrolyte support and a few μιη thickness for so-called cathode support cells.

 Cell C2 comprises a cathode 2.2 and anode 4.2, between which an electrolyte 6.2 is disposed. All electrolytes are of solid type.

 The cathodes 2.1, 2.2 and the anodes 4.1, 4.2 are made of porous material and have for example a thickness greater than 500 μιτι, typically of the order of mm and 40 μιη respectively.

The anode 4.1 of the cell C1 is electrically connected to the cathode 2.2 of the cell C2 by an interconnecting plate 8 coming into contact with the anode 4.1 and the cathode 2.2. Moreover, she allows the power supply of the anode 4.1 and the cathode 2.2.

 An interconnecting plate 8 is interposed between two elementary cells C1, C2.

 In the example shown, it is interposed between an anode of an elementary cell and the cathode of the adjacent cell. But one could predict that it is interposed between two anodes or two cathodes.

 The interconnecting plate 8 defines with the adjacent anode and cathode channels for the circulation of fluids. More specifically, they define anode compartments 9 dedicated to the flow of gases at the anode 4 and cathode compartments 11 dedicated to the flow of gas at the cathode 2.

 In the example shown, an anode compartment 9 is separated from a cathode compartment 11 by a wall 9.11. In the example shown, the interconnecting plate 8 further comprises at least one duct 10 delimiting with the wall 9.11, the anode compartments 9 and the cathode compartments 11.

In the example shown, the interconnecting plate comprises a plurality of conduits 10 and a plurality of anode 9 and cathode compartments 11. Advantageously, the conduit 10 and the compartments have hexagonal honeycomb sections, which allows to increase the density of compartments 9, 11 and ducts 10. As shown in FIG. 1A, steam is circulated to each cathode 2.1, 2.2.

 The arrows 12 in FIG. 1A thus clearly represent the path in the anode 9 and cathode compartments 11.

 As represented in FIG. 1B, the architecture of the electrolyser further makes it possible to connect the first end 10.1 of the conduit 10 to a supply of water vapor via another conduit not shown and to connect the second end 10.2 of the conduit 10 to the cathode compartment 11. The arrow 14 symbolizes the return flow of water vapor since its flow in the conduit 10 (arrow 16) to the cathode compartment 11.

 It is also possible to provide for the circulation of a draining gas in the anode compartments 9 to evacuate the oxygen (see arrows 13). The arrows

12 and 13 of FIGS. 1A and 1B thus clearly represent the simultaneous path in the anode and cathode compartments 11. It goes without saying that in the context of the invention the symbolized flow can just as easily be done in the other direction (arrows 12 and

13 in opposite direction).

 The inventor found that at the outlet end of each cathode, water vapor mixed with the produced hydrogen remained: this water vapor is therefore surplus compared to the electrolysis reactions which take place upstream.

It is known to treat this surplus water vapor by separating it from the hydrogen produced, the most of the time by means of condensers arranged downstream of the electrolyser.

 The inventor then thought to create one or more vortices upstream of the outlet, that is to say upstream of the outlet opening dedicated to the collection of the product hydrogen.

Indeed, the relative density between the water vapor and the hydrogen produced in the mixture arriving near the outlet of each elemental electrolysis cell is equal to 9 since the molar mass of hydrogen is equal to 2 g. -mol ^-1 while that of water vapor is equal to 18 g-mol ^-1 .

 Thus, by creating one or more vortices in the circulation flow of the mixture consisting of the hydrogen produced and the excess water vapor, the two types of molecules (¾ and ¾0) are subjected to a differentiated centrifugal force. is to promote the centrifugation of heavy molecules (¾0) and the extraction of light molecules (¾).

 This phenomenon of ejection of the molecules of the water vapor at the exit is all the more intense as one approaches the exit.

 FIGS. 2 and 2A show the means for creating the vortices to which the inventor has thought in the architecture of electrolysers with interconnection plates 8 previously described.

Each interconnecting plate 8 is constituted by an assembly of two stamped sheets 8.1, 8.2 partially forming stamping recesses in the form of grooves 80. As shown in Figures 2 and 2A, the assembly 8 comprises at least one opening 84 through each of the two assembled sheets.

 This opening 84 and made in a zone Z differently stamped than the recesses, at the end of the grooves 80. This zone Z differently stamped recesses may be unsworn.

 In zone Z, which is differently pressed at the end of grooves 80, holes 83 pass through only one of the two plates 8.1 and are regularly distributed around the periphery of opening 84.

 The diameter of the holes 83 is of the order of 1 mm but it can be lower. Preferably, the number of holes 83 is even so as to promote rotation of the vortices alternately. Thus, as shown in FIG. 2, the holes 83 are twelve in number and regularly spaced around the opening 84.

 The assembly of the two plates 8.1, 8.2 in the differently stamped zone Z delimits a passage 840 between the two plates 8.1, 8.2 and between the holes 83 and the opening 84 (FIG. 2A).

 The grooves 80 are the grooves dedicated to the collection of the hydrogen produced. Similarly, the opening 84 is the opening dedicated to the recovery of the hydrogen produced by the electrolysis reaction: it usually constitutes part of a collection assembly called clarinet and in which a pierced pipe (not shown) has climbed.

Due to the presence of the holes 83 of diameter less than or equal to 1 mm and the flow rate of At the entrance to zone Z, the mixture (excess water vapor and produced hydrogen) that arrives in this zone Z undergoes several vortices in parallel with tangential velocities greater than 100 m / s.

 The mixture therefore undergoes an acceleration which is calculated with the following formula:

 Y R

 in which :

 γ: Acceleration,

 V: tangential velocity,

 R: Exit hole radius.

100x100 _η7 , _2s

 Let v = = 10 m / s, that is to say one

 0001

acceleration close to 1 million times the terrestrial acceleration.

 With such an acceleration, the lighter hydrogen molecules tend to be evacuated through the holes 83 in fluid communication with the recovery opening 84 (see arrow 15 in FIG. 2A). The water molecules in the vapor of Excess water heavier than those of hydrogen tend to be ejected outwards and are therefore available to undergo electrolysis in zone Z, that is to say within the same electrolyser.

As shown in FIG. 2, provision is made to advantageously make the end 800 of the grooves 80 upstream of zone Z such that a jet of hydrogen and water vapor is created in said end 800. in addition, the jet has at the outlet of this end a flow tangential to the axis of each of the holes 83. The phenomenon of vortices created by the holes 83 is furthermore favored.

 FIG. 3 schematically shows the shape of the vortex-induced hydrogen gas stream V created by a hole 83, the arrows representing the direction of ejection of the water molecules.

 FIG. 4 illustrates the increase in the overall yield provided by the invention in an EHT electrolyser:

 the curve 3 in continuous lines represents the evolution of the average production as a function of the increase in the flow of water vapor in an electrolyser EHT according to the state of the art,

 the curve 5 in broken lines represents the evolution of the average production as a function of the increase in the flow rate of water vapor in an EHT electrolyser according to the invention,

the straight line L _T in dashed lines schematizes the evolution of the average production as a function of the increase in the flow of water vapor in the theoretical case where 100% of water vapor conversion is perfectly obtained; hydrogen.

It is clear that thanks to the invention the curve 5 is closer than the curve 3 of the theoretical straight line L _T. In other words, thanks to the creation of vortices according to the invention, it tends to approach a rate of conversion to water vapor close to 100%.

The invention that has just been thus consists in creating one or more vortices in an area upstream of the recovery zone, that is to say one or vortices tangentially to the axis of the recovery holes of the gases resulting from the electrochemical reaction, by slowing down the evacuation of the reaction gas (H2 in the example) and by promoting again an electrochemistry with gas or vapor which constitutes the (s) constituent (s) initial (ux).

 It is pointed out that compared to the various state-of-the-art vortex-forming processes that serve to separate two constituents, here there is only one gas / vapor inlet and one gas outlet, the vortex being created (s) tangentially to the axis of the recovery hole of the reaction gas. And unlike vortices created according to the state of the art by which we eject the lighter molecules to the outside, it creates according to the invention vortices to eject the heavier molecules to the outside, it is ie those of the initial constituent (s).

 The advantages of the invention which has just been described are numerous.

 Indeed, by integrating vortex creation means directly within an elementary cell of electrolysis, the advantages are as follows:

 - increase in overall yield: indeed, for the same production, it is not necessary to put more water in motion, there is less water to condense,

- increased efficiency, simplicity of implementation: simple holes to be made within the high temperature electrolyser,

 - Improved compactness by the fact that there is less water vapor to circulate, and condense output and thereby it reduces the size of the heat exchangers.

 Although described with reference to a high temperature electrolyser, the solution according to the invention is applicable to any electrochemical process in which the reaction gas has a molar mass lower than the initial constituent (s) (ux) in vapor form or of gas, insofar as the vortex (s) according to the invention makes it possible (tentatively) to separate by centrifugation the heavier molecules of the initial constituent (s) (ux) from the reaction gas. The constituent (s) initial (ux) suffered (ssen) t therefore again the electrochemical reaction in the upstream zone immediately near the outlet by which the reaction gas is recovered.

 For example, in a PEMFC proton fuel cell, the reaction that occurs at the cathode is written as follows:

0 ₂ + 4H ⁺ + 4th ^" -> 2H ₂ 0.

 By creating vortices according to the invention at the cathode outlet, it is possible to better evacuate the water vapor produced than the supply oxygen.

Claims

An electrochemical process for producing a reaction gas of lower molecular weight than that of the initial constituent (s) in the form of gas or vapor, wherein the gas or vapor is circulated of the initial constituent (s) (ux) and the reaction gas is recovered in the circulation path of the initial constituent (s) (ux), characterized in that at least one vortex is created in a zone upstream of the recovery zone of the reaction gas, the vortex being capable of separating the reaction gas produced from the initial constituent (s) (ux) still present (s) in order to make this ( s) last (s) an electrochemistry in said upstream zone. 2. A method of electrolysis of water at high temperatures according to claim 1, implemented by at least one elemental electrolysis cell (C1, C2 ..., Cn) formed of a cathode (2.1, 2.2). , an anode (4.1, 4.2) and an electrolyte (6.1, 6.2) interposed between the cathode and the anode, in which at least water vapor is circulated in contact with the cathode, an inlet end at an outlet end through which the produced hydrogen is recovered, and in which at least one vortex is created in an area upstream of the outlet end, the vortex being suitable for ) to separate the hydrogen produced water vapor still present in order to subject it to electrolysis in said upstream zone. 3. Electrolysis method according to claim 2 at temperatures between 700 ° C and 1000 ° C. 4. Electrolysis method according to claim 2 or 3, wherein a plurality of vortices are created in parallel with each other in the zone upstream of the outlet end. The electrolysis method of claim 2 or 3, wherein a plurality of vortices are formed in series from each other in the region upstream of the outlet end. 6. Electrolysis method according to one of the preceding claims, wherein each vortex is created with a tangential velocity at least equal to 80 m / s, preferably greater than 100 m / s. 7. Electrolysis method according to one of the preceding claims, wherein each vortex is created in such a way as to obtain an acceleration greater than 10 ⁶ m / s ² . Electrochemical reactor comprising a stack of elementary electrochemical cells (C1, C2 ... Cn) each formed of a cathode (2.1, 2.2), an anode (4.1, 4.2) and an electrolyte (6.1). , 6.2) interposed between the cathode and the anode, at least one interconnecting plate (8) being arranged between two adjacent elementary cells and in contact an electrode with an electrode of one of the two elementary cells and an electrode of the other of the two elementary cells, the interconnecting plate delimiting at least one cathode compartment (11) and at least one anode compartment (9) for the circulation of fluids respectively at the cathode and the anode, characterized in that it comprises means (83) for creating at least one vortex in a zone Z2 upstream of the outlet end (82) of the cathode compartments and / or anode compartments . 9. The electrochemical reactor of claim 8, wherein the means for creating the vortex (s) are constituted by holes (83) drilled in the at least one interconnecting plate upstream of the outlet end of the cathode compartments. 10. Reactor according to claim 9, wherein the diameter of the holes is less than 1 mm. 11. Plate (8), intended to be used as an interconnecting plate in a reactor according to one of claims 8 to 10, consisting of an assembly of two plates (8.1, 8.2) partially stamped forming stamped recesses. in the form of grooves (80), the assembly comprising at least one opening (84) each passing through the two assembled sheets and made in a zone Z which is differently stamped than the recesses at the end (800) of the grooves and holes (83). ) passing through only one (8.1) of the two sheets also made in the area differently stamped end of the grooves and being distributed at the periphery of the opening (84); the diameter of the holes being of the order of 1 mm or less and the assembly of the two sheets in the differently embossed zone delimits a passage (840) between the two sheets (8.1, 8.2) and between the holes (83) and the opening (84) at the periphery of which they are made. The plate of claim 11, wherein the number of holes (83) is even. 13. Plate according to claim 11 or 12, wherein the end (800) of the grooves is made in such a way that a jet of gas or gas and vapor mixture is created in said end, the jet having in in addition to a flow tangential to one of the holes (83).