Degassing device for an electrolysis plant, and electrolysis plant

Abstract

The present invention relates to the technical field of electrolysis and very particularly to an electrolysis plant for producing dihydrogen (H2) and dioxygen (O2) by electrolysis of water. According to the present invention, the plant comprises a degassing device (1) which comprises an opening for a first gas-liquid mixture supply pipe (11), an opening for a liquid discharge pipe (12) arranged below the level of the gas-liquid interface (15) of the 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). Furthermore, the device of the invention comprises one or more additional openings for one or more additional gas-liquid mixture supply pipes (21, 22), said one or more additional gas-liquid mixture supply pipes (21, 22) being arranged such that the jets of gas-liquid mixture introduced into the degassing chamber (14) via the supply pipes (11, 21, 22) intersect within the gas-lye mixture in the degassing chamber (14).

Description

Degassing device for an electrolysis plant and electrolysis plant.

[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 a degassing device which can be used in an installation for the production of dihydrogen and dioxygen by electrolysis of water. Another aspect of the invention relates to an installation for the production of dihydrogen and dioxygen by electrolysis of water containing such a degassing device. Yet 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 do not mix. The installation includes an outlet for hydrogen and electrolyte flowing on the cathode side (catholyte) and an outlet for oxygen and electrolyte on the anode side (anolyte). In other words, these are two separate flows so that there is a gas-liquid separator dedicated to separating hydrogen from the catholyte, and a gas-liquid separator for separating oxygen from the anolyte. The liquid outlets of the two gas-liquid separators are then mixed before feeding back into the electrolyzer stack. In both flows, at the electrolyzer stack outlet, the liquid phase (lye) is loaded with gas bubbles. At the outlet of the gas-liquid separator, there are only a few gas bubbles left 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 several reasons, it is important to separate the gas from the lye. First, the more gas is separated from the electrolyte, the more gas is produced, which contributes to the good electrochemical efficiency of the process. Second, the H2 / O2 mixture is highly explosive. If the separation is not carried out correctly, a significant quantity of gas, commonly called "residual gas", is entrained at the liquid outlet of the gas-liquid separator. During the next circulation in the electrolyzer 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 surrounding the degassing chamber. The gas-liquid mixture from the channel can pass into the degassing chamber via a separation element. This assembly thus allows the mixture to be cooled in the degassing chamber.

[0010] The principle of gas bubble extraction from the liquid phase is based on Archimedes' principle. The efficiency of the separation depends mainly on gravity and the difference in density between the liquid and gas phases, but also on 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 a degassing device that allows for virtually complete degassing of the exhausts (hydrogen / lye and oxygen / 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 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] Statement of the invention

[0015] According to the invention, this problem has been solved with a degassing device according to claim 1. According to the prior art, the lye-dihydrogen mixtures from several electrolyzer stacks are combined in a single pipe before being sent in a single jet into the degassing device. Similarly, the lye-dioxygen mixtures from several stacks are combined in a single pipe before being sent in a single jet into the degassing device. The inventor considered that it was possible not to combine these jets, to take advantage of their number and to inject them separately into the degassing device. In the case of a single electrolyzer stack, the inventor considered that it was possible to divide the lye-dihydrogen or lye-dioxygen mixture jet into two or more jets before injecting them into the respective degassing devices.It is then appropriate to arrange the supply pipes of the degassing chamber with gas-liquid mixture in such a way that the jets of gas-liquid mixture introduced into the degassing chamber by these supply pipes interact with each other. By the expression "interact with each other", it is meant that the jets of gas-liquid mixture intersect within the gas-lye mixture in the degassing chamber, the gas bubbles contained in the gas-lye mixture then being able to collide more likely, quickly and regularly than with a device according to the prior art so as to promote the creation of larger gas bubbles within the gas-lye mixture itself. In other words, the coalescence of the gas bubbles is accentuated following the crossing of the jets in the gas-lye mixture contained in the gas-liquid separation device.As a consequence, the contents of the gas-lye mixture in the gas-liquid separator contain gas bubbles which are more easily extracted from the gas-lye mixture as a result of their increased size. The extraction mechanism follows the same pattern as described in the prior art, namely that i) the gas bubbles rise to the gas-liquid interface due to gravity and the liquid-gas density ratio, pass into the gas volume above the interface and end their course by escaping through the gas discharge pipe of the degassing chamber and ii) the liquid phase flows through the liquid discharge pipe arranged at the bottom of the separation device. With identical dimensions of the gas-liquid separator, this liquid phase contains significantly fewer gas bubbles compared to that which can be extracted from a conventional gas-liquid separator with a single feed.

[0016] The configuration providing the best interactions between the jets entering the degassing chamber is to arrange the feed pipes so that the jets intersect at an angle a between 15 and 180°. Below 15°, the jets are almost parallel and their interactions are less strong. From an angle a of 90°, the interactions are optimal. At 180° the jets meet head-on and the interactions are maximum.

[0017] According to the invention, gas-liquid jets can therefore be injected into the degassing chamber of the device in two or more jets. As many jets as desired can be provided. However, it should be taken into account that by dividing a jet into several jets, the quantity of lye-gas mixture and the energy of the incoming jets are divided accordingly. It is therefore advisable to keep this number reasonable. For example, it is considered reasonable not to divide the incoming jet into more than three jets. However, this constraint can be overcome by supplying energy to the jets entering the degassing chamber, for example by propelling or accelerating them using a pump or an injector, or by reducing the inlet section, namely by reducing the section of the supply pipes.

[0018] The degassing chamber of the gas-liquid separator can have a horizontal or vertical main axis.

[0019] Ideally, the liquid-gas mixture feed opening of the degassing chamber is located opposite, along the main axis of said degassing chamber, at least one of the outlet openings of the degassing chamber. Thus the liquid or the gas respectively follow longer paths in the degassing chamber before being evacuated and the separation is more efficient.

[0020] Apart from this, it should also be noted that the precise location of the discharge openings of the degassing chamber is not critical, i.e. the design of the degassing device may have some flexibility in choosing the location of these openings. Of course, the discharge opening for the degassed liquid phase must be located below the gas-liquid interface of the degassing chamber, for example through the bottom wall or one of the side walls of the degassing chamber. Similarly, the discharge opening for the gaseous phase must be located above the gas-liquid interface of the degassing chamber, for example through the top wall or one of the side walls of the degassing chamber.

[0021] According to another of its aspects, the invention relates to a water electrolysis installation comprising a degassing device as defined above. The electrolysis installation may comprise an alkaline electrolyser, a membrane electrolyser or a high-temperature electrolyser. Preferably, an alkaline electrolyser is used. It is possible to provide a sensor for detecting the quantity of residual gas at the outlet of the degassing chamber. The information measured by the sensor is supplied to a control module of a valve allowing, depending on the level of gas detected in the liquid, to reinject the liquid evacuated from the degassing chamber into the degassing chamber in order to refine the separation or to supply an intermediate tank with the liquid discharged from the degassing chamber where it is mixed with the liquid phase coming from the other gas-liquid separator.

[0022] According to yet another of its aspects, the invention also relates to a method for degassing a gas-liquid mixture from an electrolysis installation as described above. According to this method of the invention, - part of the gas-liquid mixture is introduced through the first supply pipe into the degassing device, - one or more other portions of the gas-liquid mixture is (are) introduced through one or more additional feed pipes into the degassing chamber. According to the invention, the jets of gas-liquid mixture introduced into the degassing chamber through the feed pipes intersect within the gas-liquid mixture in the degassing chamber. Advantageously, at least one of the jets injected into the degassing chamber is accelerated, propelled or ejected into the degassing chamber.

[0023] Brief description of the figures

[0024] The invention will now be described by means of figures which have no other purpose than to illustrate the present invention. These figures represent schematically.

[0025] Fig. 1 a degassing device according to the prior art arranged horizontally

[0026] Fig. 2 a degassing device according to the prior art arranged vertically

[0027] Fig. 3 a degassing device according to the invention arranged horizontally

[0028] Fig. 4 a degassing device according to the invention arranged vertically

[0029] In Figs. 1 to 4, 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 includes a gas discharge pipe, gas having been separated from the liquid phase, which can then either be discharged from the installation or combined with the same gas from the electrolyser 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. We see. however, 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. It can also be seen that the degassing device can be arranged along a horizontal axis A (Figs. 1 and 3) or vertical axis (Figs. 2 and 4) depending on the construction requirements for example.

[0030] The degassing devices according to the invention shown in Figs. 3 and 4 show an additional supply pipe 21 through which the degassing chamber 14 is supplied with a gas-liquid mixture. The degassing chamber 14 is therefore supplied with a gas-liquid mixture by the two supply pipes 11 and 21. Fig. 4 also shows another additional supply pipe 22 through which the degassing chamber 14 is supplied with a gas-liquid mixture. The degassing chamber 14 is therefore supplied with a gas-liquid mixture by the three supply pipes 11, 21 and 22. The supply pipes 11 and 21 intersect at least partially within the gas-liquid mixture in the degassing chamber 14. The trajectories of the jets emerging from these pipes therefore have a partial or, preferably, total intersection. An additional supply line 22 is visible in Fig. 4.In this figure, the three jets intersect in the same area of ​​the degassing device; this embodiment is advantageous but is not essential. Furthermore, the configurations could have been reversed or even other gas-liquid mixture supply lines could have been added to the degassing chamber 14. In the illustrated embodiment of the invention, the supply lines are positioned in the same vertical plane. In another embodiment of the invention, the supply lines are positioned in the same horizontal plane.

[0031] As explained above, a pump can be provided to accelerate the jet injected into the degassing chamber 14 via the pipe 11, or via the pipe 21 or 22 or via several of them.

[0032] It can be seen in Fig. 3 that the jets of gas-liquid mixture introduced by the pipes 11 and 21 are arranged so as to cross at an angle a of 90°. The jets of gas-liquid mixture introduced by the pipes 11 and 22 are arranged so as to cross at an angle a of 90°. It can be seen in Fig. 3 that the degassing chamber 14 contains two additional gas-liquid mixture supply pipes (21 and 22). Said pipes (21 and 22) are arranged in such a way that the jets coming from pipes 11 and 21 intersect at an angle of approximately 90°, that the jets coming from pipes 11 and 22 intersect at an angle of approximately 135° and that the jets coming from pipes 21 and 22 intersect at an angle of approximately 45°. It would also have been possible to envisage intersecting the three jets at an angle of 90°. In Fig.4 only one additional pipeline 21 has been shown; it is understood that other pipelines can still be added. In others. embodiments of the invention, other configurations characterized by other angular values ​​are also to be taken into consideration.

[0033] List of drawing references: 1 Degassing device 11 Gas-liquid mixture supply pipe 12 Liquid discharge pipe 13 Gas discharge pipe 14 Gas-liquid separation chamber 15 Gas-liquid interface 21 Additional supply lines 22 Additional supply lines A Main axis of the gas-liquid separator

Claims

Claims 1. Degassing device (1) for an electrolysis installation 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); characterized in that the degassing chamber (14) comprises - one or more additional opening(s) for one or more additional supply pipe(s) (21, 22) for gas-liquid mixture, said one or more additional supply pipe(s) (21, 22) for gas-liquid mixture being arranged in such a way that the jets of gas-liquid mixture introduced into the degassing chamber (14) by the supply pipes (11, 21, 22) intersect within the gas-liquid mixture in the degassing chamber (14).

2. Degassing device (1) according to the preceding claim in which the degassing chamber (14) comprises an additional opening for an additional supply pipe (21) of gas-liquid mixture.

3. Degassing device (1) according to the preceding claim further comprising a pump configured to accelerate at least one of the jets injected into the degassing chamber (14).

4. Degassing device (1) according to one of claims 2 or 3, further comprising a reduction in the section of the supply pipe configured to accelerate at least one of the jets injected into the degassing chamber (14).

5. Degassing device (1) according to any one of the preceding claims in which at least two jets intersect at an angle (a) of between 15° and 180°.

6. Degassing device (1) according to the preceding claim in which at least two jets intersect at an angle (a) of between 90° and 180°.

7. Electrolysis installation comprising a degassing device according to any one of the preceding claims.

8. Electrolysis installation according to the preceding claim in which the electrolysis cell operates on the principle of alkaline electrolysis.

9. Method for degassing a gas-liquid mixture from an electrolysis installation according to claim 7 in which - a part of the gas-liquid mixture is introduced through the first supply pipe (11) into the degassing device, - one or more other part(s) of the gas-liquid mixture is (are) introduced through one or more additional supply pipe(s) (21, 22) into the degassing chamber (14), in which the jets of gas-liquid mixture introduced into the degassing chamber (14) through the supply pipes (11, 21, 22) intersect within the gas-lye mixture in the degassing chamber (14).

10. A degassing method according to claim 9, wherein at least one of the jets injected into the degassing chamber (14) is accelerated, propelled or ejected into the degassing chamber (14).

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