Electrolysis facility with degassing device and associated method

Abstract

The present invention relates to the technical field of electrolysis and, most particularly, to an electrolysis facility for producing dihydrogen (H2) and dioxygen (O2) by water electrolysis. According to the present invention, the facility comprises a degassing device (1) which comprises a degassing chamber (14) provided with: an opening for a first pipe (11) for supplying a gas / liquid mixture; an opening for a liquid-discharge pipe (12) arranged below the level of the gas / liquid interface (15) of the degassing chamber (14); and an opening for a gas-discharge pipe (13) arranged above the level of the gas / liquid interface (15) of the degassing chamber (14). According to the invention, the degassing chamber (14) further comprises one or more additional openings for one or more additional pipes (21, 22, 23, 24) for supplying a gas / liquid mixture, wherein each of the pipes for discharging the gas / liquid mixture of each of the electrolyser stacks is connected to a pipe (11, 21, 22, 23, 24) for supplying a gas / liquid mixture to the degassing chamber (14), a flow-regulating device being configured on each of the supply pipes (11, 21, 22, 23) so that the jets injected into the degassing chamber (14) have substantially identical speeds, at least in pairs.

Description

Installation of and method of de

[0001] Description

[0002] The present invention relates to the technical field of electrolysis and more particularly to an electrolysis installation for the production of dihydrogen (H2) and dioxygen (O2) by electrolysis of water. According to a first of its aspects, the invention relates to an installation for the production of dihydrogen and dioxygen by electrolysis of water. Another aspect of the invention relates to a degassing method.

[0003] Indication of prior art

[0004] The need to reduce greenhouse gas production and use renewable energy is now well known. Dihydrogen is an alternative to hydrocarbons because it is an easily storable energy vector, unlike electricity, and its oxidation releases a very high energy content (285 kJ / mol).

[0005] There are several known ways to produce gaseous dihydrogen; the most advantageous is to electrolyze the water molecule because it is a high-yield reaction that does not directly produce CO2, unlike the widely used processes of reforming methane, coal and hydrocarbons.

[0006] There are three main types of electrolyzers for water electrolysis: - alkaline electrolysers (AWE), which are characterised by the use of a liquid electrolyte which allows the transfer of hydroxyl ions (OH') from the cathode to the anode, - high-temperature electrolysers, whose electrolyte is a ceramic; and - membrane electrolysers (PEM), whose electrolyte is a proton-conducting ion exchange membrane.

[0007] In all three cases, the system must be supplied with water of very high purity (supplying, in the case of alkaline electrolysers, an electrolytic solution of sodium hydroxide (NaOH) or potassium hydroxide (KOH)). In the remainder of the description, for reasons of brevity, reference will be made to an alkaline electrolyser, but it is understood that the present invention also applies to the membrane electrolyser (for example a proton exchange membrane).

[0008] According to the well-known method of the prior art, an electrolytic solution (known by the English term lye) is brought into a set of electrolytic cells (known as an electrolyzer stack) through a specific inlet. The electrolytic solution passes through the electrolyzer stack. The water is decomposed into gaseous molecules of dihydrogen, H2, at the cathode), and dioxygen, O2, at the anode. A diaphragm generally separates the anode from the cathode so that, under normal conditions, dihydrogen and dioxygen do not mix. The installation includes an outlet for dihydrogen and electrolyte flowing on the cathode side (catholyte) and an outlet for dioxygen and electrolyte flowing on the anode side (anolyte). In other words, these are two separate flows so that there is a gas-liquid separator dedicated to the separation of dihydrogen from the catholyte, and a gas-liquid separator for the separation of dioxygen from the anolyte. The liquid outputs of the two gas-liquid separators are then mixed before feeding back into the electrolyzer stack. In both streams, at the outlet of the electrolyzer stack, the liquid phase (lye) is loaded with gas bubbles. At the outlet of the gas-liquid separator, only a few gas bubbles remain in the lye evacuated through the lower orifice of the gas-liquid separator dedicated to the liquid phase while the majority of the gas phase is extracted from the gas-liquid separator through the upper orifice of the gas-liquid separator. For various reasons, it is important to separate the gas from the lye. First of all, the more the gas is separated from the electrolyte, the more gas is produced, which contributes to the good electrochemical efficiency of the process. Secondly, the H2 / O2 mixture is highly explosive.If the separation is not carried out correctly, a significant amount of gas, commonly called "residual gas", is carried away at the liquid outlet of the gas-liquid separator. During the next circulation in the electrolyser stack (the electrolyte rotates in a closed loop) some of this gas passes into the other compartment and therefore to the wrong side.

[0009] These gas-liquid separators, well known in the art, comprise a degassing chamber provided with an opening for a gas-liquid mixture supply pipe, an opening for a liquid discharge pipe arranged below the level of the gas-liquid interface of the degassing chamber and an opening for a gas discharge pipe arranged above the level of the gas-liquid interface of the degassing chamber. Each of the outlets of the electrolyzer stack for the dihydrogen-lye mixtures on the one hand and dioxygen-lye on the other hand is connected to such a gas-liquid separator. Figs. 1 and 2 schematically represent known gas-liquid separators aligned respectively along a horizontal or vertical main axis A. Document FR-A1-2949479 for example, describes such gas-liquid separators. Another gas separator is known from document EP-A1-4001464.In this installation, the electrolysis products are highly corrosive (alkaline) and heated to high temperatures. The degassing installation must therefore be able to withstand these extreme conditions, which requires the use of very expensive materials such as nickel alloys. This document proposes a solution whereby the gas-liquid mixture to be degassed is introduced in several fractions. The hottest fractions are introduced directly into the part of the degassing chamber above the gas-liquid interface while colder fractions are introduced into a channel circumscribing the degassing chamber. The gas-liquid mixture from the channel can pass into the degassing chamber via a separation element. The assembly thus makes it possible to cool the gas-liquid mixture in the degassing chamber.

[0010] The principle of extracting gas bubbles from the liquid phase is based on Archimedes' principle. The efficiency of separation depends mainly on gravity as well as the difference in density between the liquid and gas phases but also in viscosity (friction of the gas bubbles in the liquid part). The gas-liquid mixture must therefore remain in the degassing chamber for a sufficient period of time to allow all the gas bubbles to be extracted from the lye. In the following description, such gas-liquid separators will be referred to as gravity gas-liquid separators. These gravity gas-liquid separators are characterized by substantial dimensions. In some gas-liquid separators, equipment can be inserted to accelerate the separation (for example a honeycomb structure) or to standardize the flow and have a uniform residence time for all the streamlines.Gas bubbles still present in the liquid phase can be quantitatively significant, i.e. not all gas bubbles can be extracted from the liquid phase for evacuation via a dedicated evacuation pipe on the top or side wall of the degassing chamber. This poses several problems. As already mentioned above, the efficiency of the electrolyzer stack suffers from this gas loss. Furthermore, in conventional electrolysis plants, the two lye fractions evacuated from the gas-liquid separator are combined and mixed in an intermediate tank before being reinjected into the electrolyzer stack in a closed loop.Due to incomplete separation, a potentially significant amount of residual hydrogen and oxygen may be reinjected into the electrolyzer stack, so that the residual oxygen ends up on the cathode side while the hydrogen moves towards the anode. As already mentioned, it is well known that the hydrogen / oxygen gas mixture is explosive even at a fairly low concentration, and this situation is dangerous for personnel and the installation. The gases thus produced also have very poor purity, requiring an additional purification step.

[0011] One solution to this problem is to increase the size of the gas-liquid separators, which in turn creates new problems related to the additional cost, complexity of manufacturing and transporting these gas-liquid separators, as well as the increase in the size of the production plant.

[0012] It would therefore be desirable to be able to provide an electrolysis installation including a degassing device allowing practically complete degassing of the exhausts (dihydrogen / lye and dioxygen / lye from the electrolytic cells). Ideally, such a degassing device should be able to provide the expected result when the system is used at full load (high exhaust flow rate) or at reduced load (low exhaust flow rate).

[0013] It is also necessary to take into account the fact that the gas-liquid separators of electrolysers do not always produce dihydrogen and dioxygen at their nominal load (unlike similar systems for other industries or applications) and that the system must be efficient regardless of the quantity of gas to be separated. Indeed, when the As the volume of gas decreases, the purity of the gases deteriorates because proportionally the coalescence of the larger and easier to extract gas bubbles is not the same.

[0014] Another problem is the surface area occupied by the electrolysis installation. Indeed, in known devices, each electrolyzer stack is connected to a separate degassing device. This configuration therefore tends to generate the design of very large installations. The inventor observed that if one tried to feed a degassing device through the gas-lye outlet pipes of several electrolyzer stacks, the liquid contained in the degassing device is subjected to currents coming from several feed pipes according to asymmetrical forces, and a phenomenon of rotation of the flow (recirculation effect) appears. Gas bubbles are trapped in this recirculation, which constrains their movements. The optimal flow, which would be a uniform flow in the direction of the length of the gas-liquid separator, can no longer be ensured, which reduces the separation performance.The recirculation phenomenon in turn creates recirculation pockets. The gas bubbles present at the inlet of the gas-liquid separator at the gas-liquid interface are drawn towards the lower part of the degassing device.

[0015] Ultimately, this recirculation phenomenon within the gas-lye mixture causes the quantity of gas bubbles at the bottom of the gas-liquid separator to increase drastically, which means that the "residual" liquid phase, leaving the degassing device through the opening for the liquid discharge pipe located on the lower face of the device, contains more gas bubbles and therefore accentuates all the consequences described previously with regard to the introduction of the residual gas at the liquid outlet of the degassing device into the electrolyser stack. In other words, the gas bubbles could not naturally follow the conventional path by first reaching the gas-liquid interface before being spontaneously extracted through the orifice located on the upper face of the gas-liquid separator.

[0016] The inventor therefore set about eliminating this recirculation phenomenon that he had discovered.

[0017] Statement of the invention

[0018] This objective is achieved by implementing an electrolysis installation comprising at least two electrolyser stacks and a degassing device as defined in claim 1. Indeed, it has been observed that by sizing, aligning and orienting the supply pipes of the degassing device appropriately, it is possible to obtain better homogenization of the flow, i.e. to eliminate or at least very significantly limit the formation of these recirculation currents) and that, quite surprisingly, it is possible to open into a degassing chamber supply pipes with a lye-gas mixture coming from several electrolyser stacks. without negative consequences on the efficiency of gas-lye separation. As a consequence, it is possible to reduce the overall size of the electrolysis installation.

[0019] Advantageously, the gas-liquid mixture supply pipes to the degassing chamber are present in an even number and are sized, aligned and oriented in the degassing chamber in an identical manner in pairs. It has indeed been observed that it is not absolutely essential to ensure that all the supply pipes are configured in an identical manner to obtain the desired effect and that it is sufficient for the supply pipes to the degassing chamber to be paired in pairs. In addition to the configurational aspect, this pairing corresponds to the fact that the supply pipes have identical diameters, gas flow rates and lye flow rates.To achieve this, the paired feed lines are both connected to electrolyzer stacks producing the same gas flow rate and in which the circulating lye flow rate is similar while considering that the diameter of the feed lines is identical. Even more advantageously, the feed lines of the degassing chamber are paired in a linear progression starting from the central pair. This means that the central pair is paired and that, starting from this central pair, each of the following feed lines is paired with the feed line which is symmetrical to it with respect to the central pair.

[0020] According to another advantageous embodiment of the invention, the gas-liquid mixture supply pipes of the degassing chamber are present in odd numbers and are sized, aligned and oriented in the degassing chamber in an identical manner two by two considering a single central supply pipe. The notion of pairing defined previously considering an even number of supply pipes remains valid in the present case with an odd number of supply pipes. Even more advantageously, the supply pipes of the degassing chamber are paired following a linear progression starting from the single central pipe.This means that the central pipe is unpaired and that, starting from this central pipe, each of the following supply pipes is paired with the supply pipe which is symmetrical to it with respect to the central pipe.

[0021] According to a preferred embodiment of the invention, the gas-liquid mixture supply pipes are aligned along a substantially vertical axis in a wall of the degassing chamber and open into the degassing chamber along a substantially vertical axis.

[0022] According to a preferred embodiment of the invention, the gas-liquid mixture supply pipes are aligned along a substantially horizontal axis in a wall of the chamber degassing and open into the degassing chamber along a substantially horizontal axis.

[0023] According to another embodiment of the invention, the gas-liquid mixture supply pipes to the degassing chamber open into the degassing chamber orthogonally to the wall.

[0024] According to another preferred embodiment of the invention, the gas-liquid mixture supply pipes of the degassing chamber are equidistant, at least two by two (i.e. the paired supply pipes are arranged symmetrically with respect to the central pair).

[0025] According to another variant of the invention, the gas-liquid mixture supply pipes of the degassing chamber open into the degassing chamber at an identical distance from the wall, at least two by two (i.e. the paired supply pipes open into the degassing chamber at a distance from the wall symmetrically with respect to the central pair).

[0026] According to another of its aspects, the invention relates to a degassing method as defined in claim 8.

[0027] Advantageously, at least some of the gas-liquid mixture supply pipes to the degassing chamber are present in even number and are sized, aligned and oriented in the degassing chamber in an identical manner two by two and said some of the supply pipes are supplied with flows having identical properties two by two.

[0028] Even more advantageously, the supply pipes with gas-liquid mixture of the degassing chamber are supplied by flows with a lye flow rate, a gas flow rate, a temperature and a pressure which are identical two by two.

[0029] Preferably, the installation is configured so that the fastest jets are furthest from the central pair of supply pipes and the slowest jets originate from the central pair. Even more preferably, the paired pairs of supply pipes follow a progression in which the speed of the jets increases from the center outward.

[0030] Brief description of the figures

[0031] The invention will now be described by means of figures which have no other purpose than to illustrate the present invention. These figures schematically represent:

[0032] Fig. 1 a degassing device according to the prior art

[0033] Figs. 2 and 3, degassing devices according to the invention

[0034] Figs. 4 to 8, details of the wall of the degassing chamber of the degassing device showing the configuration of the supply pipes

[0035] Fig. 9, a degassing device according to the invention seen from above

[0036] In Figs. 1 to 9, different degassing devices 1 are shown. All contain a degassing chamber 14. For example gas-water or gas-lye. The gas can be dihydrogen or dioxygen. The degassing chamber 14 is supplied by a supply pipe 11 of the gas-liquid mixture coming from the electrolyzer stack. In certain cases (not shown in the figures), the degassing chamber 14 can also be supplied with gas-liquid mixture coming from the liquid discharge pipe 12 of the degassing chamber 14 by means of a loop controlled by a valve if a sensor has detected that the quantity of gas present in the discharge of the degassing chamber 14 was greater than a predetermined value. The degassing chamber 14 also comprises a gas discharge pipe which can then either be discharged from the installation or combined with the same gas coming from the electrolyzer stack.It will be noted that the gas discharge pipe 13 is always arranged above the gas-liquid interface 15. It may be located, for example, in the upper wall or in the side wall(s) of the degassing chamber 14. Similarly, the liquid discharge pipe 12 is always arranged below the gas-liquid interface 15. It may be located, for example, in the lower wall (bottom wall) or in the side wall(s) of the degassing chamber 14. The precise location of the discharge pipe 12 or 13 is not critical. It can be seen, however, that in all the cases shown, the discharge pipe 12 or 13 has been arranged opposite, that is to say at the furthest distance from the supply pipe 11 of the degassing chamber 14 in order to allow a longer path for the liquid in the degassing device 1. The degassing device 1 can be arranged along a horizontal axis A (Figs.1 to 3) or vertical (not shown) depending on construction requirements for example.

[0037] The degassing devices 1 according to the invention shown in Figs. 2 to 9 show at least one additional supply line 21 through which the degassing chamber 14 is supplied with gas-liquid mixture. The degassing chamber 14 is therefore supplied with gas-liquid mixture by the two supply lines 11 and 21. Figs. 4 to 9 also show further additional supply lines 22 and 23 (and 24 in Fig. 8) through which the degassing chamber 14 is supplied with gas-liquid mixture. The degassing chamber 14 of the device of Figs. 4 to 7 and 9 is therefore supplied with gas-liquid mixture by the four supply lines 11, 21, 22 and 23 and that of Fig. 8 by the five supply lines 11, 21, 22, 23 and 24. The configurations could have been reversed or even further supply lines for the gas-liquid mixture could have been added to the degassing chamber 14.

[0038] Fig. 2 therefore shows a degassing device 1 with two supply pipes 11, 21 for gas-lye mixture. As can be seen, the two supply pipes 11, 21 open into the same wall of the degassing chamber 14. They are aligned along a substantially vertical axis and open into the degassing chamber 14. degassing 14 at a substantially identical distance from the wall. It can also be seen that the two feed pipes 11, 21 open orthogonally to the wall of the degassing chamber 14 and have symmetrical flows (dotted arrow). This makes it possible to obtain flows producing a homogeneous circulation of the liquid in the degassing chamber 14 (i.e., the substantial elimination of any recirculation current) following the pairing of the feed pipes 11 and 21. Consequently, the residual gas bubbles of the lye-gas mixture are not trapped in recirculation pockets and can escape from the liquid phase, which makes it possible to obtain good separation. It should be noted that the configuration shown in Fig. 3 is also particularly advantageous.

[0039] Fig. 3 therefore shows a degassing device 1 with four supply pipes 11, 21, 22 and 23 for gas-lye mixture. As can be seen, the four supply pipes 11, 21, 22 and 23 open into the same wall of the degassing chamber 14, having the following pairing, 11 with 23 and 21 with 22. They are aligned along a substantially vertical axis and open into the degassing chamber 14 at a substantially identical distance from the wall. It can also be seen that the four supply pipes 11, 21, 22 and 23 open orthogonally to the wall of the degassing chamber 14. The pair of supply pipes 21 and 22 constitute the central pair.

[0040] Figs. 4 to 7 each show the details of a different configuration of the supply pipes 11, 21, 22 and 23 opening into the degassing chamber 14. These Figs show four supply pipes opening into the degassing chamber 14, but the invention could just as well have been illustrated with six, eight, ten, etc. supply pipes following the principles illustrated. In other words, the inventor has clearly demonstrated that, regardless of the geometric configuration proposed (even or odd number of supply pipes opening into the degassing chamber 14), the paired supply pipes are supplied by flows whose properties are identical.

[0041] In all these Figs., the supply pipes 11, 21, 22 and 23 open into the degassing chamber 14. In Figs. 4 to 6, the supply pipes 21, 22 of the central pair are relatively close and the supply pipes 11, 23 of the external pair open on either side of the central pair 21, 22 at a distance from the nearest supply pipe of the central pair which is further away than that between the two supply pipes of the central pair. Fig. 4 illustrates a configuration in which the four supply pipes open into the degassing chamber 14 at an identical distance from the wall. Fig. 5 illustrates a configuration in which the two supply pipes of the central pair open at a greater distance from the wall than the two supply pipes of the outer pair and Fig. 6, the reverse configuration. Fig. 7 illustrates a configuration in which the supply pipes 21, 22 of the central pair are relatively far apart and the supply pipes 11, 23 of the outer pair open on either side of the central pair 21, 22 at a distance from the nearest supply pipe of the central pair which is closer than that between the two supply pipes of the central pair.

[0042] In order to allow homogeneous circulation of the liquids in the degassing device 1, it is also possible to provide in the electrolysis installation that a flow regulating device (not shown) is configured on each of the supply pipes 11, 21, 22, 23 so that the jets injected into the degassing chamber 14 have substantially identical speeds, at least two by two.

[0043] Fig. 8 illustrates an embodiment in which, in addition to the paired supply lines 11, 21, 22 and 23, the device comprises an additional supply line 24 which is central.

[0044] Fig. 9 shows another embodiment of the degassing device in which the supply pipes 11, 21, 22 and 23 which open into the degassing chamber are aligned along a substantially horizontal axis.

[0045] List of drawing references: I Degassing device II Gas-liquid mixture supply line 12 Liquid discharge pipe 13 Gas discharge pipe 14 Gas-liquid separation chamber 15 Gas-liquid interface 21 Additional supply line 22 Additional supply line 23 Additional supply line 24 Additional supply line

Claims

Claims 1. Electrolysis installation comprising at least two electrolyser stacks and a degassing device (1) comprising a degassing chamber (14) provided - an opening for a first supply pipe (11) for gas-liquid mixture; - an opening for a liquid discharge pipe (12) arranged below the level of the gas-liquid interface (15) of the degassing chamber (14); - an opening for a gas discharge pipe (13) arranged above the level of the gas-liquid interface (15) of the degassing chamber (14); the degassing chamber (14) comprising - one or more additional opening(s) for one or more additional supply pipe(s) (21, 22, 23, 24) for gas-liquid mixture, in which each of the gas-liquid mixture discharge pipes of each of the electrolyser stacks is connected to a supply pipe (11, 21, 22, 23, 24) for gas-liquid mixture of the degassing chamber (14), a flow regulating device being configured on each of the paired supply pipes (11, 21, 22, 23) so that the jets injected into the degassing chamber (14) have substantially identical speeds, at least two by two.

2. Electrolysis installation according to claim 1, in which the pairs of supply pipes (11, 21, 22, 23) of gas-liquid mixture to the degassing chamber (14) are paired in a linear progression starting from the most central pair (21, 22).

3. Electrolysis plant according to claim 1 or 2, in which an additional supply line (24) is arranged in the center of the paired supply lines (11, 21, 22, 23).

4. Electrolysis installation according to any one of the preceding claims, in which the supply pipes (11, 21, 22, 23, 24) of gas-liquid mixture to the degassing chamber (14) are aligned along a substantially vertical or horizontal axis in a wall of the degassing chamber (14).

5. Electrolysis installation according to any one of the preceding claims, in which the supply pipes (11, 21, 22, 23, 24) of gas-liquid mixture from the degassing chamber (14) open into the degassing chamber (14) orthogonally to the wall.

6. Electrolysis installation according to any one of the preceding claims, in which the paired supply pipes (11, 21, 22, 23) of gas-liquid mixture to the degassing chamber (14) are equidistant from the center, at least two by two.

7. Electrolysis installation according to any one of the preceding claims, in which the paired supply pipes (11, 21, 22, 23) of gas-liquid mixture from the degassing chamber (14) open into the degassing chamber (14) at an identical distance from the wall, at least two by two.

8. Method for degassing a gas-liquid mixture from an electrolysis installation according to any one of the preceding claims in which - a part of the gas-liquid mixture is introduced through the first supply pipe (11) into the degassing chamber (14) of the degassing device, - the liquid is evacuated from the degassing chamber (14) by a liquid evacuation pipe (12) arranged below the level of the gas-liquid interface (15) of the degassing chamber (14); - the gas is evacuated from the degassing chamber (14) by a gas evacuation pipe (13) arranged above the level of the gas-liquid interface (15) of the degassing chamber (14); - one or more other part(s) of the gas-liquid mixture is (are) introduced by one or more additional supply pipe(s) (21, 22, 23, 24) of gas-liquid mixture from the degassing chamber (14), characterized in that the gas-liquid mixture is injected into the degassing chamber (14) by the supply pipes (11, 21, 22, 23, 24) with substantially identical speeds, at least two by two.

9. Degassing method according to claim 8 in which at least some of the supply pipes (11, 21, 22, 23, 24) for supplying gas-liquid mixture to the degassing chamber (14) are present in even number and are sized, aligned and oriented in the degassing chamber (14) in an identical manner two by two and in which said some of the supply pipes (11, 21, 22, 23, 24) are supplied with flows having identical properties two by two.

10. Degassing method according to claim 9 in which the supply pipes (11, 21, 22, 23, 24) are supplied with gas-liquid mixture from the degassing chamber (14) by flows with a lye flow rate, a gas flow rate, a temperature and a pressure which are identical in pairs.

11. A degassing method according to any one of claims 8 to 10 wherein the fastest jets are found furthest from the center of the feed pipes and the slowest jets come from the central pair (21, 22) or the single unpaired central feed pipe (24).

12. A degassing method according to the preceding claim wherein the pairs of paired feed pipes follow a progression in which the jet speed increases from the central pair to the outermost pair.

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