Water electrolysis facility with a degassing chamber comprising a cyclone

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 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). Furthermore, in the device of the invention, the degassing chamber (14) comprises a cyclonic gas / liquid separator (2) supplied with a gas / liquid mixture by the pipe (11) for supplying a gas / liquid mixture to the degassing chamber (14).

Description

WATER ELECTROLYSIS PLANT WITH A DEGASSING CHAMBER INCLUDING A CYCLONE

[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 one of its aspects, the invention relates to an installation for the production of dihydrogen and dioxygen by electrolysis of water containing a degassing device.

[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. The document FR-A1-2949479 for example, describes such gas-liquid separators.

[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 manage to. be extracted from the liquid phase for evacuation via an ad hoc evacuation pipe on the top or side wall of the degassing chamber. This poses several problems. As already indicated above, the efficiency of the electrolyzer stack suffers from this loss of gas. Furthermore, in conventional electrolysis installations, the two fractions of lye 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 the incomplete separation, a potentially significant quantity 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 goes 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 which requires 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] Furthermore, degassing devices are known for separating by flotation a dispersed liquid phase and / or suspended solids from a continuous liquid phase containing free gas (for example from document WO-A1-2005 / 056483) or for separating (at least partially) oil, water, gas and solids from hydrocarbon production well fluids (for example from document WO-A1-2006 / 090140). These devices are not intended for use in an electrolysis installation intended to separate gases such as dihydrogen or dioxygen from lye.

[0015] Statement of the invention

[0016] The cyclonic gas-liquid separator is well known in the prior art. Its operation relies on centrifugal forces as the driving force for the separation of the liquid and gas phases, unlike gravity-driven gas-liquid separators. The operating principle of the cyclonic gas-liquid separator is based on swirling, in other words the rotation of the incoming gas-lye mixture. This swirl produces a centrifugal force that drives the densest phase, the lye, towards the walls of the cyclonic gas-liquid separator, while the less dense phase, the gas bubbles, remains in the center of said cyclonic gas-liquid separator. It is also well known that the efficiency of the cyclonic gas-liquid separator is highly dependent on the incoming flow rates. Indeed, at low incoming flow rates, the energy linked to the flow is not sufficient to effectively separate the gas bubbles.However, alkaline electrolysers aim to produce hydrogen with a low carbon footprint. They are therefore generally linked to renewable energy production, which can vary greatly depending on demand. As a result, the volume of gas-liquid mixture that must be separated is also variable. Thus, the cyclonic gas-liquid separator alone is not sufficient to meet the needs of this application.

[0017] According to the invention, this problem has been solved with a water electrolysis installation according to claim 1. The inventor has in fact noticed that by combining in an electrolysis installation a cyclonic gas-liquid separator and a gravity gas-liquid separator, it is possible to obtain a satisfactory separation of the gas and the liquid. When the cyclone gas-liquid separator is coupled to a gravity gas-liquid separator, the latter carries out an additional separation which makes it possible to separate the gaseous phase at the outlet of the cyclonic gas-liquid separator. At partial load, the efficiency of the cyclonic separation is lower, but the gravity separation is better due to an increase in the residence time.

[0018] The invention therefore relates to a water electrolysis installation comprising a particular degassing device as defined below. The electrolysis installation may comprise an alkaline electrolyser, a membrane electrolyser or a high-temperature electrolyser. Preferably, an alkaline electrolyser is used. As will be explained below, the degassing device according to the invention allows the use of a degassing device of reduced size. It has been observed that according to the invention, the degassing device can provide the expected result when the installation is used at full load (high discharge flow rate) or at reduced load (low discharge flow rate).

[0019] In the installation according to the invention, the cyclonic gas-liquid separator is arranged in the degassing chamber and is supplied by the gas-liquid mixture supply pipe to the degassing chamber.

[0020] Preferably, the cyclonic gas-liquid separator is provided with a first outlet opening for the gas emerging into the degassing chamber above the level of the gas-liquid interface of the degassing chamber; and a second outlet opening for the liquid emerging into the degassing chamber below the level of the gas-liquid interface of the degassing chamber. This configuration makes it possible to prevent liquid from being entrained into the gas phase by gas bubbles which would percolate through said liquid. Similarly, the discharge of the liquid phase below the level of the gas-liquid interface makes it possible to prevent the entrainment of gas into the liquid phase.

[0021] The inventor also observed that the presence of the cyclonic gas-liquid separator within the gas-liquid separator thus allows a first separation of the gaseous molecules from the gas-lye mixture. Since the gas-lye mixture is already undergoing strong degassing, the residence time of the gas-liquid mixture in the device can be significantly lower than in the case of a gravity gas-liquid separator alone. In this configuration, the size of said gravity gas-liquid separator can therefore be reduced compared to a conventional installation.

[0022] When the cyclone gas-liquid separator is coupled to a gravity gas-liquid separator, the latter performs an additional separation which allows the gas phase to be separated at the outlet of the cyclone gas-liquid separator.

[0023] According to an advantageous variant of the invention, to further improve the efficiency of the system, a deflector can be placed in the degassing chamber, under the liquid discharge opening of the cyclonic gas-liquid separator. Said plate thus prevents gas bubbles still possibly present in the liquid from being dispersed in the bottom of the degassing chamber. Without wishing to be bound by this hypothesis, the inventor considers that small bubbles (for example less than 100 μm) do not rise quickly enough to the surface to be able to be evacuated. On the contrary, it is believed that these small bubbles follow the current lines of the liquid phase. The presence of the deflector would make it possible to deflect the trajectory of these small bubbles towards the surface where they can more easily be extracted from the liquid phase.The deflector can be made of a flat, convex or concave plate which further multiplies this effect of deflecting the trajectory of small bubbles.

[0024] The degassing chamber of the gas-liquid separator can have a horizontal or vertical main axis.

[0025] Ideally, the liquid-gas mixture feed opening of the degassing chamber is located opposite, along the main axis of the degassing chamber, at least one of the outlet openings of the degassing chamber. This allows the liquid or gas respectively to follow longer paths in the degassing chamber before being evacuated and the separation is more efficient.

[0026] 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.

[0027] It is possible to provide a sensor to detect 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 evacuated from the degassing chamber where it is mixed with the liquid phase coming from the other gas-liquid separator.

[0028] 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.

[0029] Fig. 1 a degassing device for an electrolysis installation according to the prior art arranged horizontally

[0030] Fig. 2 a degassing device for an electrolysis installation according to the prior art arranged vertically

[0031] Fig. 3 a degassing device for an electrolysis installation according to the invention arranged horizontally

[0032] Fig. 4 a degassing device for an electrolysis installation according to the invention arranged vertically

[0033] In Figs. 1 to 4, different degassing devices 1 for an electrolysis installation 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. However, it can be seen that in all the cases shown, the discharge pipe 12 or 13 has been arranged opposite, i.e. 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.We also see 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 construction requirements for example.

[0034] The devices of the prior art electrolysis installations of Figs. 1 and 2 are generally larger in size than the devices of the electrolysis installations according to the invention of Figs. 3 and 4 because their efficiency is lower and a longer residence time in the degassing device is necessary.

[0035] The degassing devices 1 of the electrolysis installations according to the present invention contain a cyclonic gas-liquid separator 2 whose feed opening 21 is connected to the gas-liquid mixture feed pipe 11 of the degassing chamber 14. The cyclonic gas-liquid separator 2 is provided with a first outlet opening 23 for the gas emerging into the degassing chamber 14 above the level of the gas-liquid interface 15 of the degassing chamber 14 and with a second outlet opening 22 for the liquid emerging into the degassing chamber 14 below the level of the gas-liquid interface 15. A deflector 3 is arranged under the liquid outlet so as to intercept the jet of liquid discharged from the cyclonic gas-liquid separator 2. This prevents the residual gas bubbles from being dispersed in the liquid present in the degassing chamber 14, more particularly in the bottom of said degassing chamber 14.The deflector 3 may consist of a flat, convex or concave plate. The deflector 3 is supported by an arm (not shown) which may be connected to one of the walls (for example, the bottom or side) of the degassing chamber 14 or to the cyclonic gas-liquid separator 2 or to any construction element present in the degassing chamber 14. A flat deflector is shown in Fig. 3 and a concave deflector in Fig. 4. The reverse configuration could just as well have been shown. It can be seen that in Figs. 3 and 4, the liquid discharge pipe 13 is shown in the top wall of the degassing chamber 14. The pipe 13 could just as well have been shown in a side wall of the degassing chamber 14. The liquid discharge pipe 12 is shown in the bottom wall in Fig. 3 and in a side wall in Fig. 4. We could just as well have represented the reverse configuration.

[0036] List of drawing references: 1 Gas-liquid separator 11 Gas-liquid mixture supply line 12 Liquid discharge pipe 13 Gas discharge pipe 14 Gas-liquid separation chamber 15 Gas-liquid interface 2 Cyclonic gas-liquid separator 21 Cyclonic gas-liquid separator feed opening 22 Cyclonic gas-liquid separator liquid discharge opening 23 Gas discharge opening of the cyclonic gas-liquid separator 3 Deflector A Main axis of the gas-liquid separator

Claims

Claims 1. Water electrolysis installation comprising a degassing chamber (14) provided - an opening for a 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) further comprises - a cyclonic gas-liquid separator (2) supplied with gas-liquid mixture by the gas-liquid mixture supply pipe (11) from the degassing chamber (14).

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

3. Electrolysis installation according to one of the preceding claims in which the cyclonic gas-liquid separator (2) has - a supply opening (21) connected to the supply pipe (11) for gas-liquid mixture to the degassing chamber (14); - a first outlet opening (23) for the gas emerging into the degassing chamber (14) above the level of the gas-liquid interface (15) of the degassing chamber (14); and - a second outlet opening (22) for the liquid emerging into the degassing chamber (14) below the level of the gas-liquid interface (15) of the degassing chamber (14).

4. Electrolysis installation according to the preceding claim in which a deflector (3) is arranged under the liquid outlet opening (22).

5. Electrolysis installation according to the preceding claim in which the deflector (3) consists of a flat or concave plate.

6. Electrolysis installation according to any one of the preceding claims, in which the degassing chamber (14) has a horizontal main axis (A).

7. Electrolysis installation according to any one of claims 1 to 6, in which the degassing chamber (14) has a vertical main axis (B).

8. Electrolysis installation according to any one of claims 6 or 7, in which the supply pipe (11) for liquid-gas mixture of the degassing chamber (14) is located opposite, along the main axis (A) of the degassing chamber (14), at least one of the discharge pipes (23, 13) of the degassing chamber (14).

9. Electrolysis installation according to claim 8, in which the supply pipe (11) for liquid-gas mixture of the degassing chamber (14) is located opposite, along the main axis (A) of the degassing chamber (14), the discharge pipes (23, 13) of the degassing chamber (14).

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