Water electrolysis plant comprising one or more degamers connected in series, with static mixer in supply pipe

Abstract

The present invention relates to the technical field of electrolysis and, in particular, to a degassing device for an electrolysis plant for producing dihydro (H2) and dioxygen (O2) by electrolyzing water. According to the invention, the apparatus comprises a degassing device (1, 101) comprising a degassing chamber (14, 114), the degassing chamber (14, 114) is provided with an opening for a gas-liquid mixture supply pipe (11, 111), an opening for a liquid discharge pipe (12, 112) arranged below the level of the gas-liquid interface (15, 115) of the degassing chamber (14, 114), and an opening for a gas discharge pipe (13, 113) arranged above the level of the gas-liquid interface (15, 115) of the degassing chamber (14, 114). Furthermore, a static mixer (21, 121) is inserted into the gas-liquid mixture supply tube (11, 111).

Description

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[0001] This invention relates to the field of electrolysis technology, and more specifically to an electrolysis apparatus for producing dihydrogen (H2) and hydrogen peroxide (O2) by water electrolysis. According to one aspect of the invention, the invention relates to a degassing device that can be used in an apparatus for producing dihydrogen and hydrogen peroxide by water electrolysis. Existing technology

[0002] It is now widely recognized that there is a need to reduce greenhouse gas emissions and utilize renewable energy sources. Dihydrogen is a substitute for hydrocarbons because, unlike electricity, it is an energy carrier that can be easily stored, and its oxidation releases a very large amount of energy (285 kJ / mol).

[0003] Several known methods exist for producing gaseous dihydrogen; the most advantageous is the electrolysis of water molecules because, unlike the widely used processes of methane, coal, and hydrocarbon reforming, it is a high-yield reaction that does not directly produce CO2.

[0004] Three main types of electrolyzers are known for water electrolysis:

[0005] - An alkaline electrolyzer (AWE) is characterized by the use of a liquid electrolyte that causes hydroxyl ions (OH-) to form... - The material is transferred from the cathode to the anode.

[0006] - High-temperature electrolyzers, whose electrolyte is ceramic; and

[0007] - A membrane electrolyzer (PEM) whose electrolyte is a proton-conducting ion-exchange membrane.

[0008] In all three cases, very high purity water must be supplied to the system (in the case of an alkaline electrolyzer, an electrolyte solution of sodium hydroxide (NaOH) or potassium hydroxide (KOH) must be supplied). Although the remainder of this specification will refer to alkaline electrolyzers for the sake of brevity, it should be understood that the invention is also applicable to membrane electrolyzers (e.g., proton exchange membranes).

[0009] According to methods well-known in the prior art, an electrolyte solution (called alkali) is introduced into a set of electrolytic cells (called an electrolyzer stack) through a specific inlet. The electrolyte solution flows through the electrolyzer stack. Water is broken down into gaseous molecules, dihydrogen (H2) at the cathode and hydrogen peroxide (O2) at the anode. A diaphragm typically separates the anode and cathode so that dihydrogen and O2 do not mix under normal conditions. The device includes outlets for dihydrogen and the electrolyte circulating on the cathode side (cathode electrolyte) and for O2 and the electrolyte circulating on the anode side (anode electrolyte). In other words, there are two separate streams, and therefore there are gas-liquid separators specifically for separating dihydrogen from the cathode electrolyte and for separating O2 from the anode electrolyte. The liquid outlets of the two gas-liquid separators are then mixed and fed back into the electrolyzer stack. In both streams, at the outlet of the electrolyzer stack, the liquid phase (alkali) is filled with bubbles. At the outlet of the gas-liquid separator, only a small number of bubbles remain in the alkali solution discharged through the lower orifice dedicated to the liquid phase, while most of the gas phase is extracted from the separator through the upper orifice. Separating the gas from the alkali solution is important for several reasons. First, the more gas separated from the electrolyte, the more gas is produced, which contributes to a good electrochemical yield for the method. Second, the H2 / O2 mixture is highly explosive. If separation is not performed correctly, a significant amount of gas (often referred to as "residual gas") is entrained at the liquid outlet of the gas-liquid separator. During the next cycle in the electrolyzer stack (where the electrolyte rotates in a closed loop), some of this gas enters another compartment, and thus, the wrong side.

[0010] These gas-liquid separators, well known in the art, include a degassing chamber having an opening for a gas-liquid mixture supply pipe, an opening for a liquid discharge pipe disposed horizontally below the gas-liquid interface of the degassing chamber, and an opening for a gas discharge pipe disposed horizontally above the gas-liquid interface of the degassing chamber. Each of the outlets of the electrolyzer stack for the dihydrogen-alkali solution and the hydrogen peroxide-alkali solution mixture is respectively connected to such a gas-liquid separator. Figure 1 and 2 The diagrams schematically represent known gas-liquid separators aligned along either the horizontal or vertical main axis A. For example, document FR-A1-2949479 describes such a separator. Document WO-A1-2020 / 254211 is another example.

[0011] The principle of extracting bubbles from the liquid phase is based on Archimedes' principle. The efficiency of separation depends primarily on gravity and the density difference between the liquid and gas phases, and also on viscosity (friction of bubbles in the liquid portion). Therefore, the gas-liquid mixture must remain in the degassing chamber for a sufficient time to allow all bubbles to be extracted from the alkali solution. In the remainder of this specification, this type of gas-liquid separator will be designated by the term gravity gas-liquid separator. These gravity gas-liquid separators are characterized by their large size. In some gas-liquid separators, devices can be inserted to accelerate separation (e.g., honeycomb structures) or to homogenize the flow and ensure that all streamlines have a uniform residence time. The number of bubbles remaining in the liquid phase can be significant; in other words, not all bubbles can be extracted from the liquid phase to be discharged through specially designed exhaust pipes on the upper or side walls of the degassing chamber. This presents several problems. As noted above, the output of the electrolyzer stack is affected by this gas loss. Furthermore, in conventional electrolysis equipment, the two alkaline fractions discharged from the gas-liquid separator are combined and mixed in an intermediate tank, and then fed back to the electrolyzer stack in a closed loop. Due to incomplete separation, potentially significant amounts of residual dihydrogen and residual hydrogen peroxide may be fed back to the electrolyzer stack, resulting in residual hydrogen peroxide on the cathode side and dihydrogen being directed to the anode. As already noted, dihydrogen / hydrogen peroxide gas mixtures are known to be explosive even at relatively low concentrations, and this situation is hazardous to personnel and equipment. The resulting gas also has a very general purity, requiring additional purification steps.

[0012] One solution to this problem is to increase the size of the gas-liquid separator, which in turn raises new issues related to additional costs, the complexity of manufacturing and transporting these gas-liquid separators, and the increased size of production operations.

[0013] Therefore, it is desirable to provide a water electrolysis device that allows for near-complete degassing of the effluents (dihydrogen / alkali and hydrogen peroxide / alkali from the electrolyzer). Ideally, this type of water electrolysis device should be able to provide the desired results when the system is operating at full load (high discharge flow rate) or at reduced load (low discharge flow rate).

[0014] In practice, it should also be considered that the gas-liquid separator in the electrolyzer does not always produce dihydrogen and hydrogen peroxide at its nominal load (unlike similar systems used in other industries or applications), and that the system must be efficient regardless of the amount of gas to be separated. This is because the purity of the gas decreases as the gas volume decreases, since the coalescence of larger and more easily extracted bubbles is proportionally different.

[0015] Mixers designed to promote close mixing of two components are known in the prior art (see, for example, document WO-A1-2013 / 126346). Summary of the Invention

[0016] According to the invention, this problem is solved using the apparatus as defined in claim 1. A static mixer is an apparatus for continuously mixing a fluid or a fluid and a material in another phase (solid or gas). Such an apparatus allows mixing of these elements, but it can also be used with gases or for mixing gases and liquids. Particularly surprisingly, such a mixing apparatus can be used to achieve the opposite effect, i.e., to separate gases from liquids rather than mix them. The inventors have observed that, under the action of a static mixer, the gas-alkali mixture passing through the static mixer undergoes very strong turbulence. In the present case, this turbulence cannot disrupt the already formed bubbles and thus produces the opposite effect. Therefore, using the proposed solution, only small bubbles remain in the static mixer. Furthermore, this turbulence causes the bubbles contained in the mixture to coalesce, which promotes the formation of larger bubbles, which can then be more easily extracted from the liquid in a gravity gas-liquid separator downstream of the static mixer. The gas separation mechanism follows the same scheme developed in gravity gas-liquid separators, i) bubbles rise to the gas-liquid interface due to gravity and the liquid-gas density ratio, and end their journey by being discharged through a dedicated gas discharge pipe located in the upper part of the degassing chamber; and ii) the liquid phase flows through a liquid discharge pipe located in the lower part of the degassing chamber.

[0017] Many static mixers exist that can be used according to the present invention. The operating principle of a static mixer is described in document US 3286992. Many geometries may be suitable for such mixers: spiral, twisted, perforated strip, with barbs or spikes, as well as wire windings, fins, and vortex generators, also known as cyclones, etc. Advantageously, static mixers are formed by spiral inserts. According to another advantageous variant of the invention, the static mixer is formed by a cyclone. The reason is that both types of static mixers convert a portion of the translational energy of the flow into rotational energy and allow for strong merging of bubbles, which can then be more easily extracted from the liquid.

[0018] Therefore, the present invention relates to a water electrolysis apparatus comprising one or more electrolyzer stacks and a degassing device as described above, the degassing device being defined by a connection between a static mixer and a separator (gravity or cyclone) downstream of the static mixer. The degassing device is supplied by a supply pipe connected to a liquid phase discharge pipe of at least one electrolyzer stack. As explained above, such an apparatus allows for efficient and rapid separation of gas-liquid mixtures to a degree that reduces the size of the degassing device.

[0019] According to an advantageous variant of the invention, the apparatus includes an additional degassing device upstream or downstream of the degassing device defined above. A first degassing device is supplied by a supply pipe connected to the discharge pipe of at least one electrolyzer stack. There, only large bubbles are discharged, and their breakup in the static mixer is eliminated. Thus, the first gas-liquid separator is small in size, separating only bubbles larger than 300 µm (ideally larger than 200 or 100 µm). The liquid discharge pipe of this first degassing device is connected to the supply pipe of a second degassing device. Therefore, the two degassing devices are arranged in series. The static mixer is arranged in the supply pipe of the first degassing device, the supply pipe of the second degassing device, or both supply pipes.

[0020] Two degassing devices installed in series can be aligned along the horizontal or vertical main axis A in all possible combinations (horizontal-horizontal, horizontal-vertical, vertical-horizontal, or vertical-vertical).

[0021] It is also possible to provide one or more additional degassing devices.

[0022] The preferred and simplest solution is that the gas / liquid flow reaches a first gas-liquid separator, where the largest bubbles and the largest volume of gas are extracted, and then merging is achieved in a conduit (equipped with a static mixer) connecting this gas-liquid pre-separator to a second gas-liquid separator. The static mixer can then generate very strong agitation without the risk of the large bubbles that have already formed bursting. The two gas outlets can be connected together and processed together. In this case, due to the connected containers, the two levels of the gas-liquid separator must be identical. Attached Figure Description

[0023] The invention will now be described with reference to the accompanying drawings, which serve no purpose other than to illustrate the invention. In these drawings, schematically:

[0024] Figure 1 This refers to a degassing device for a horizontally arranged water electrolysis unit, based on existing technology.

[0025] Figure 2 This refers to a degassing device for a vertically arranged water electrolysis unit, based on existing technology.

[0026] Figure 3 A degassing device for a horizontally arranged water electrolysis apparatus according to the present invention;

[0027] Figure 4 This describes a degassing device for a vertically arranged water electrolysis apparatus according to the present invention;

[0028] Figure 5 and 6This represents two parts of an electrolysis device with two degassing units connected in series (the preferred solution in terms of efficiency and the simplest).

[0029] Figures 1 to 4 This represents various degassing devices 1 used in water electrolysis equipment. All include a degassing chamber 14. For example, a gas-water or gas-alkali mixture. The gas can be dihydrogen or hydrogen peroxide. The degassing chamber 14 is supplied by a supply pipe 11 for a gas-liquid mixture from the electrolyzer stack. In some cases (not shown), if a sensor has detected that the amount of gas present in the discharge from the degassing chamber 14 is greater than a predetermined value, a gas-liquid mixture from a liquid discharge pipe 12 of the degassing chamber 14 can also be supplied to the degassing chamber 14 via a valve-controlled loop. The degassing chamber 14 also includes a gas discharge pipe from which the gas has been separated from the liquid phase; this gas can then be discharged from the equipment or recombined with the same gas from the electrolyzer stack. It should be noted that the gas discharge pipe 13 is always arranged above the gas-liquid interface 15. It can be located, for example, in the upper wall or side wall of the degassing chamber 14. Similarly, the liquid discharge pipe 12 is always arranged below the gas-liquid interface 15. It can be located, for example, in the lower wall (bottom wall) or side wall of the degassing chamber 14. The precise location of the discharge pipe 12 or 13 is not critical, but care must be taken to ensure that vortices that could entrain gas are not formed there. A vortex-breaking device is advantageous in preventing this phenomenon. However, it can be seen that in all the cases shown, the discharge pipe 12 or 13 has been arranged on the opposite side, that is, at the furthest distance from the supply pipe 11 to the degassing chamber 14, in order to allow for a longer path for the liquid in the degassing device 1. It can also be seen that, for example, depending on construction requirements, the degassing device can be along a horizontal axis (…). Figure 1 and Figure 3 ) or vertical axis A ( Figure 2 and Figure 4 Arrangement.

[0030] Figure 3 and Figure 4 The degassing device shown has a static mixer 21 in its supply pipe.

[0031] Figure 5 and 6 This represents an assembly of two degassing units installed in series. The first of the two degassing units 1 includes a degassing chamber 14. For example, a gas-water or gas-alkali mixture may be used. The gas may be dihydrogen or hydrogen peroxide. The degassing chamber 14 is supplied by a supply pipe 11 for a gas-liquid mixture from the electrolyzer stack. The degassing chamber 14 also includes a gas discharge pipe 13 and a liquid discharge pipe 12. Figure 5 and Figure 6The assembly also includes a second degassing device 101 mounted in series with the first degassing device 1. The second degassing device 101 includes a degassing chamber 114 supplied by a supply pipe 111 for a gas-liquid mixture from a liquid discharge pipe 12 of the first degassing device 1. The degassing chamber 114 also includes a gas discharge pipe 113 and a liquid discharge pipe 112. Figure 5 and Figure 6 As seen in the image, the gas-liquid mixture supply pipe 111 of the second degassing device 101 includes a static mixer 121.

[0032] exist Figure 6 As seen in the diagram, the gas-liquid mixture supply pipe of the first degassing device 1 also includes a static mixer 21. Two gas outlets can be connected for common processing. In this case, due to the double connection (gas and liquid), the two free surface areas will be carefully adjusted.

[0033] List of reference numerals in the attached diagram:

[0034] 1. Gas-liquid separator

[0035] 11 Gas-liquid mixture supply pipe

[0036] 12 Liquid discharge pipe

[0037] 13 Gas exhaust pipe

[0038] 14 Gas-Liquid Separation Chamber

[0039] 15 Gas-Liquid Interface

[0040] 21 Static Mixer

[0041] 101 Gas-Liquid Separator

[0042] 111 Gas-Liquid Mixture Supply Pipe

[0043] 112 Liquid Discharge Pipe

[0044] 113 Gas Emission Pipe

[0045] 114 Gas-Liquid Separation Chamber

[0046] 115 Gas-Liquid Interface

[0047] 121 Static Mixer

[0048] The main shaft of separator A.

Claims

1. A water electrolysis apparatus or any other component comprising one or more electrolyzer stacks and degassing devices (1, 101), wherein, The degassing device (1, 101) includes a degassing chamber (14, 114), the degassing chamber having - Openings for gas-liquid mixture supply pipes (11, 111); - An opening for a liquid discharge pipe (12, 112), the opening being arranged horizontally below the gas-liquid interface (15, 115) of the degassing chamber (14, 114); - An opening for a gas discharge pipe (13, 113) arranged horizontally above the gas-liquid interface (15, 115) of the degassing chamber (14, 114), a static mixer (21, 121) inserted into the gas-liquid mixture supply pipe (11, 111), wherein the degassing device (1, 101) is supplied via the supply pipe (11, 111) which is connected to the gas-electrolyte mixture discharge pipe of at least one electrolyzer stack.

2. The water electrolysis apparatus as described in the preceding claim, wherein, The static mixer (21, 121) is formed by a spiral insert.

3. The water electrolysis equipment as described in claim 1, wherein, The static mixer (21, 121) is formed by a cyclone separator.

4. A water electrolysis apparatus comprising one or more electrolyzer stacks as claimed in any of the preceding claims, comprising two or more degassing units (1, 101) connected in series.

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