Electrolysis facility with degassing device and related methods

Abstract

The present invention relates to the technical field of electrolysis, and most particularly to an electrolysis plant for the production of dihydrogen (H2) and dioxygen (O2) by water electrolysis. According to the invention, the installation comprises a degassing device (1) comprising a degassing chamber (14) equipped with: an opening for a first tube (11) for supplying a gas-liquid mixture; an opening for a liquid discharge pipe (12) arranged horizontally below 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, in which each of the pipes for discharging the gas-liquid mixture of each of the electrolyzer stacks is connected to the pipe (11, 21, 22, 23, 24) for supplying the gas-liquid mixture to the degassing chamber (14), flow regulation means are arranged on each of the supply pipes (11, 21, 22, 23) such that the jets injected into the degassing chamber (14) have substantially the same velocity at least in pairs.

Description

Description

[0001] The present invention relates to the field of electrolysis and more particularly to an electrolysis plant for producing dihydrogen (H2) and dioxygen (O2) by electrolysis of water. According to a first aspect of the invention, the present invention relates to a plant for producing dihydrogen and dioxygen by electrolysis of water. Another aspect of the invention relates to a method of degassing. State of the art

[0002] It is now well known that there is a need to reduce the production of greenhouse gases and to use renewable energy sources. Di-hydrogen 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] There are several known ways of producing gaseous di-hydrogen; the most advantageous is the electrolysis of water molecules because, unlike the processes of methane, coal and hydrocarbon reforming, which are used in large quantities, it is a high-yield reaction that does not directly produce CO2.

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

[0005] - Alkaline electrolyzers (AWE) characterized by the use of a liquid electrolyte that transfers hydroxyl ions (OH - ) from the cathode to the anode;

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

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

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

[0009] According to methods well known in the art, an electrolyte solution, called lye, is introduced through specific inlets into a set of electrolytic cells, called electrolyzer stacks. The electrolyte solution crosses the electrolyzer stacks. Water is decomposed into gaseous molecules, dihydrogen H2 at the cathode and dioxygen O2 at the anode. A diaphragm usually separates the anode from the cathode so that dihydrogen and dioxygen do not mix under normal conditions. The installation comprises outlets for dihydrogen and electrolyte circulating on the cathode side (cathode electrolyte) and outlets for dioxygen and electrolyte circulating on the anode side (anode electrolyte). In other words, there are two separate flows and therefore gas-liquid separators dedicated to separating dihydrogen from the cathode electrolyte and gas-liquid separators dedicated to separating dioxygen from the anode electrolyte. The liquid outlets of the two gas-liquid separators are then mixed before feeding the electrolyzer stacks again. In both flows, at the outlet of the electrolyzer stacks, the liquid phase (lye) is full of gas bubbles. At the outlet of the gas-liquid separators, only a small amount of gas bubbles remains in the lye exiting through the lower orifice of the gas-liquid separator dedicated to the liquid phase, while most of the gas phase is extracted from the gas-liquid separator through the upper orifice of the gas-liquid separator. It is important to separate the gas from the lye for various reasons. First, the more gas is separated from the electrolyte, the more gas is produced, which contributes to a good electrochemical yield of the process. Second, the H2 / O2 mixture is highly explosive. If the separation is not properly done, a significant amount of gas, usually called "residual gas", is entrained at the liquid outlet of the gas-liquid separator. Some of this gas enters the other compartment and therefore the wrong side during the next cycle in the electrolyzer stacks (the electrolyte is rotated in a closed loop).

[0010] These gas-liquid separators well known in the art comprise a degassing chamber having an opening for a gas-liquid mixture supply pipe, an opening for a liquid discharge pipe arranged horizontally below the gas-liquid interface of the degassing chamber, and an opening for a gas discharge pipe arranged above the gas-liquid interface of the degassing chamber. Each of the outlets of the electrolyzer stacks for dihydrogen-lye and dioxygen-lye mixtures is connected to such a gas-liquid separator, respectively. Figure 1 and 2A known gas-liquid separator is schematically depicted, aligned along a horizontal or vertical main axis A, respectively. For example, document FR-A1- 2949479 describes such a gas-liquid separator. Another gas separator is known from document EP-A1-4001464. In this installation, the electrolysis products are highly corrosive (alkaline) and at high temperature. 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 in which the gas-liquid mixture to be degassed is introduced in several fractions. The hotter fractions are introduced directly into the part of the degassing chamber above the gas-liquid interface, while the colder fractions are introduced into a channel surrounding the degassing chamber. The gas-liquid mixture from the channel can enter the degassing chamber via a separation element. This assembly thus makes it possible to cool the gas-liquid mixture in the degassing chamber.

[0011] The principle of extraction of the gas bubbles from the liquid phase is based on the Archimedes principle. The efficiency of the separation depends mainly on the gravity and on the difference in density between the liquid and the gas phases, but also on the viscosity (friction of the bubbles in the liquid part). The gas-liquid mixture must therefore remain in the degassing chamber for a sufficiently long time to allow all the gas bubbles to be extracted from the alkaline liquid. In the remainder of this description, this type of gas-liquid separator will be designated by the term gravity gas-liquid separator. These gravity gas-liquid separators are characterized by a very large size. In some gas-liquid separators, devices can be inserted to accelerate the separation (for example, honeycomb structures) or to homogenize the flow and to make all the flow lines have a uniform residence time. The gas bubbles still present in the liquid phase can be significant in number; in other words, not all the gas bubbles manage to be extracted from the liquid phase in order to be discharged through a specific discharge pipe on the upper or lateral wall of the degassing chamber. This poses a number of problems. As already indicated above, the output of the electrolyser stack is affected by this loss of gas. In addition, in a conventional electrolysis installation, the two alkaline liquid fractions discharged from the gas-liquid separator are combined and mixed in an intermediate tank, then fed back into the electrolyser stack in a closed circuit. Due to the incomplete separation, a potentially significant amount of residual dihydrogen and residual dioxygen can be fed back into the electrolyser stack, making the residual dioxygen at the cathode side and the dihydrogen directed to the anode. As already indicated, it is known that the dihydrogen / dioxygen gas mixture is explosive even at quite low concentrations, and this situation is dangerous for the personnel and the installation. The gas thus produced also has a very general purity, which requires an additional purification step.

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

[0013] It would therefore be desirable to provide a water electrolysis plant comprising a degassing device that allows for almost complete degassing of the effluents (dihydrogen / alkali and dioxygen / alkali of the electrolytic cells). Ideally, this type of degassing device should be able to provide the expected results when the system is operated at full load (high effluent flow rate) or at reduced load (low effluent flow rate).

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

[0015] Another problem concerns the surface area occupied by the electrolysis plant. In particular, in the known devices, each electrolyzer stack is connected to a separate degassing device. This configuration tends to lead to the design of very large plants. The inventors have observed that if one tries to supply a degassing device via the gas-alkali effluent pipes of several electrolyzer stacks, the liquid contained in the degassing device is subjected to a current of liquid with asymmetric forces from the several supply pipes in line, causing a rotation of the flow (recirculation effect). Bubbles are trapped in this recirculation, which limits the movement of the bubbles. It is no longer possible to ensure optimal flow, i.e. uniform flow along the length of the gas-liquid separator, which impairs the separation performance. The recirculation phenomenon in turn creates recirculation pockets. There is a bubble present at the inlet of the gas-liquid separator, at the height of the gas-liquid interface, which is drawn toward the lower part of the degassing device.

[0016] Finally, this recirculation phenomenon within the gas-alkali mixture leads to a sharp increase in the amount of bubbles at the bottom of the gas-liquid separator, which means that the "residual" liquid phase leaving the degassing device through the opening of the liquid effluent pipe located on the lower face of the device contains more bubbles and, therefore, highlights all the consequences mentioned above regarding the introduction of residual gas at the liquid outlet of the degassing device into the electrolyzer stack. In other words, the bubbles cannot naturally follow the conventional path, first reaching the gas-liquid interface and then being spontaneously extracted through the orifice located on the upper face of the gas-liquid separator.

[0017] The present inventors therefore set out to eliminate this recirculation phenomenon that they had discovered. SUMMARY

[0018] This object is achieved by implementing an electrolysis plant as defined in claim 1, comprising at least two electrolyzer stacks and a degassing device. In particular, it has been observed that by properly sizing, aligning and orienting the supply pipes of the degassing device, a better homogenization of the flow is obtained, in other words, the formation of these recirculation liquid flows is eliminated or at least very significantly limited, and, rather surprisingly, it is possible to make the supply pipes supplying the alkali-gas mixture from several electrolyzer stacks open into the degassing chamber without negatively affecting the efficiency of the gas-alkali separation. As a result, the overall size of the electrolysis plant can be reduced.

[0019] Advantageously, the supply pipes supplying the gas-liquid mixture to the degassing chamber are present in an even number and are identically sized, aligned and oriented in pairs in the degassing chamber. It has in fact been observed that it is not absolutely necessary to ensure that all the supply pipes are identically configured to obtain the desired effect and that it is sufficient that the supply pipes to the degassing chamber are coupled in pairs. In addition to the configuration aspect, this pairing corresponds to the fact that the supply pipes have the same diameter, gas flow rate and alkali flow rate. To this end, the supply pipes of a pair are both connected to an electrolyzer stack, produce the same gas flow rate and in which the circulation alkali flow rate is similar, taking into account that the diameter of the supply pipes is the same. Even more advantageously, the supply pipes to the degassing chamber are paired in a linear progression starting from a central pair. This means that the two pipes in the center are paired and starting from this central pair, each of the subsequent supply pipes is paired with the supply pipe symmetric to it with respect to the central pair.

[0020] According to another advantageous embodiment of the present application, the supply pipes supplying the gas-liquid mixture to the degassing chamber are present in an odd number and are identically sized, aligned and oriented in pairs in the degassing chamber, with a single central supply pipe. The concept of pairing defined above with respect to an even number of supply pipes is also valid in the current case for an odd number of supply pipes. Even more advantageously, the supply pipes to the degassing chamber are paired in a linear progression starting from a single central pipe. This means that the central pipe is not paired and starting from this central pipe, each of the subsequent supply pipes is paired with the supply pipe symmetric to it with respect to the central pipe.

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

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

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

[0024] According to another preferred embodiment of the application, the supply pipes supplying the gas-liquid mixture to the degassing chamber are at least in pairs equidistant (in other words, the pairs of supply pipes are arranged about the center pair symmetrically).

[0025] According to another variant of the application, the supply pipes supplying the gas-liquid mixture to the degassing chamber open into the degassing chamber at least in pairs at the same distance from the wall (in other words, the pairs of supply pipes open into the degassing chamber at a certain distance from the wall about the center pair symmetrically).

[0026] According to another aspect of the application, the application relates to a degassing method as defined in claim 8.

[0027] Advantageously, at least some of these supply pipes supplying the gas-liquid mixture to the degassing chamber exist in even numbers and are identically dimensioned, aligned and oriented in pairs in the degassing chamber, and said some of these supply pipes are supplied in pairs with flows having identical characteristics.

[0028] Even more advantageously, the supply pipes for supplying the gas-liquid mixture to the degassing chamber are supplied in pairs with flows having identical caustic flow rates, gas flow rates, temperatures and pressures.

[0029] Preferably, the installation is configured so that the fastest jets are farthest from the center pair of supply pipes and the slowest jets come from this center pair. Even more preferably, the pairs of supply pipes pairs follow a progression whereby the jet velocity increases from the center outward. BRIEF DESCRIPTION OF DRAWINGS

[0030] The application will now be described by means of the attached drawings, which have no other purpose than to illustrate the application. In these drawings, schematically:

[0031] Figure 1 a degassing device according to the prior art is depicted

[0032] Figure 2 and Figure 3 a degassing device according to the application is depicted

[0033] Figures 4 to 8 a detail of the wall of the degassing chamber of the degassing device is depicted, showing the configuration of the supply pipes

[0034] Figure 9 a degassing device according to the application is depicted, seen from above

[0035] Figures 1 to 9Various degassing devices 1 are depicted. All comprise a degassing chamber 14. The gas can be dihydrogen or dioxygen. The degassing chamber 14 is supplied by a supply pipe 11 for a gas-liquid mixture from the electrolyser stack. In some cases (not shown in the figures), the degassing chamber 14 can also be supplied with a gas-liquid mixture from the liquid discharge pipe 12 of the degassing chamber 14 through a circuit controlled by a valve, if the sensor has detected that the amount of gas present in the discharge from the degassing chamber 14 is greater than a predetermined value. The degassing chamber 14 also comprises a pipe for discharging gas, which can then be discharged from the installation or recombined with the same gas from the electrolyser stack. It is noted that the gas discharge pipe 13 is always arranged above the gas-liquid interface 15. It can for example be located in the upper wall or in the side wall of the degassing chamber 14. Similarly, the liquid discharge pipe 12 is always arranged below the gas-liquid interface 15. It can for example be located in the lower wall (bottom wall) or in the side wall of the degassing chamber 14. The precise position of the discharge pipes 12 or 13 is not critical. However, as can be seen, in all the cases shown, the discharge pipes 12 or 13 have been arranged on opposite sides, that is to say at the greatest 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. Depending on the structural requirements, the degassing device 1 can for example be arranged along a horizontal (not shown) or vertical (shown) axis A. Figures 1 to 3

[0036] The degassing device 1 according to the application depicted in Figures 2 to 9 shows at least one additional supply pipe 21 through which a gas-liquid mixture is supplied to the degassing chamber 14. Thus, the degassing chamber 14 is supplied with a gas-liquid mixture through two supply pipes 11 and 21. Figures 4 to 9 Other additional supply pipes 22 and 23 (and 24 in Figure 8 ) are also shown, through which a gas-liquid mixture is supplied to the degassing chamber 14. Thus, the degassing chamber 14 of the device is supplied with a gas-liquid mixture through four supply pipes 11, 21, 22 and 23 in Figures 4 to 7 and Figure 9 , and through five supply pipes 11, 21, 22, 23 and 24 in Figure 8 . The configuration can be reversed, or even additional gas-liquid mixture supply pipes can be added to the degassing chamber 14.

[0037] Thus, Figure 2 ​A degassing device 1 is shown having two supply pipes 11, 21 for a 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 at substantially the same distance from the wall. It can also be seen that the two supply pipes 11, 21 open orthogonally to the wall of the degassing chamber 14 and have symmetrical flows (dashed arrows). This makes it possible to obtain, after pairing of the supply pipes 11 and 21, a flow in the degassing chamber 14 that generates a homogeneous circulation of the liquid (i.e. substantially eliminates any recirculation flow). Thus, the residual gas bubbles from the gas-lye mixture are not trapped in recirculation pockets and can escape from the liquid phase, thus achieving good separation. It is noted that, Figure 3 The configuration shown in the

[0038] Thus, Figure 3 A degassing device 1 is shown having four supply pipes 11, 21, 22 and 23 for a 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, paired as follows: 11 with 23 and 21 with 22. They are aligned along a substantially vertical axis and open into the degassing chamber 14 at substantially the same distance from the wall. As can also be seen, 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 constitutes the central pair.

[0039] Figures 4 to 7 Each shows the details of a different configuration of the supply pipes 11, 21, 22 and 23 opening into the degassing chamber 14. These figures show four supply pipes opening into the degassing chamber 14, but according to the principle illustrated, the invention can equally well be illustrated with six, eight, ten, etc. supply pipes. In other words, the inventors have clearly demonstrated that, whatever the proposed geometric configuration (an even or odd number of supply pipes opening into the degassing chamber 14), the paired supply pipes are supplied with flows having identical characteristics.

[0040] In all these figures, the supply pipes 11, 21, 22 and 23 open into the degassing chamber 14. In Figures 4 to 6 In the central pair of supply pipes 21, 22 is relatively close, and the outer pair of supply pipes 11, 23 opens on either side of the central pair 21, 22 at a distance from the nearest supply pipe of the central pair that is further than the distance between the two supply pipes of the central pair. Figure 4 A configuration is shown in which the four supply pipes open into the degassing chamber 14 at the same distance from the wall. Figure 5 A configuration is shown 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 Figure 6 The opposite configuration is shown. Figure 7A configuration is shown 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 at a distance from the nearest supply pipe of the central pair, on either side of the central pair, which distance is closer than the distance between the two supply pipes of the central pair.

[0041] To allow for uniform circulation of the liquid in the degassing device 1, a flow regulating device (not shown) can also be provided in the electrolysis plant, which flow regulating device is configured on each of the supply pipes 11, 21, 22, 23, such that the jets injected into the degassing chamber 14 have at least in pairs substantially the same speed.

[0042] Figure 8 An embodiment is shown in which, in addition to the pairs of supply pipes 11, 21, 22 and 23, the device also comprises an additional supply pipe 24 located centrally.

[0043] Figure 9 Another embodiment of the degassing device is shown, in which the supply pipes 11, 21, 22 and 23 leading to the degassing chamber are aligned along a substantially horizontal axis.

[0044] List of reference signs:

[0045] 1 degassing device

[0046] 11 gas-liquid mixture supply pipe

[0047] 12 liquid discharge pipe

[0048] 13 gas discharge pipe

[0049] 14 gas-liquid separation chamber

[0050] 15 gas-liquid interface

[0051] 21 additional supply pipe

[0052] 22 additional supply pipe

[0053] 23 additional supply pipe

[0054] 24 additional supply pipe.

Claims

1. An electrolysis plant comprising at least two electrolyzer stacks and a degassing device (1) comprising a degassing chamber (14) having - 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 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 openings for one or more additional gas-liquid mixture supply pipes (21, 22, 23, 24), wherein, each of the gas-liquid mixture discharge pipes from each of the electrolyzer stacks is connected to a supply pipe (11, 21, 22, 23, 24) for supplying gas-liquid mixture to the degassing chamber (14), flow regulating means being configured on each of the pairs of supply pipes (11, 21, 22, 23) such that the jets injected into the degassing chamber (14) have at least in pairs substantially the same velocity.

2. The electrolysis plant of claim 1, wherein, The pairs of supply pipes (11, 21, 22, 23) supplying gas-liquid mixture to the degassing chamber (14) are in linear progression starting from the most central pair (21, 22).

3. The electrolysis plant of claim 1 or 2, wherein, An additional supply pipe (24) is arranged at the center of the pairs of supply pipes (11, 21, 22, 23).

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

5. The electrolysis plant of any one of the preceding claims, wherein, The supply pipes (11, 21, 22, 23, 24) supplying gas-liquid mixture to the degassing chamber (14) open into the degassing chamber (14) orthogonally to the wall.

6. The electrolysis plant of any one of the preceding claims, wherein, The pairs of supply pipes (11, 21, 22, 23) supplying gas-liquid mixture to the degassing chamber (14) are at least in pairs equidistant with respect to the center.

7. The electrolysis plant of any one of the preceding claims, wherein, The pairs of supply pipes (11, 21, 22, 23) supplying gas-liquid mixture to the degassing chamber (14) open into the degassing chamber (14) at least in pairs at the same distance from the wall.

8. A degassing method for degassing a gas-liquid mixture in an electrolysis plant as claimed in any one of the preceding claims, wherein - a portion of the gas-liquid mixture is introduced into the degassing chamber (14) of the degassing device through the first supply pipe (11), - liquid is discharged from the degassing chamber (14) through the liquid discharge pipe (12) arranged below the level of the gas-liquid interface (15) of the degassing chamber (14); - gas is discharged from the degassing chamber (14) through the gas discharge pipe (13) arranged above the level of the gas-liquid interface (15) of the degassing chamber (14); - one or more other portions of the gas-liquid mixture are introduced through one or more additional supply pipes (21, 22, 23, 24) supplying gas-liquid mixture to 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) at least in pairs at substantially the same speed.

9. The degassing method of claim 8, wherein, At least some of the supply pipes (11, 21, 22, 23, 24) supplying gas-liquid mixture to the degassing chamber (14) exist in pairs and are identically sized, aligned and oriented in pairs in the degassing chamber (14), and wherein the some of the supply pipes (11, 21, 22, 23, 24) are supplied in pairs with flows having identical characteristics.

10. The degassing method of claim 9, wherein, The supply pipes (11, 21, 22, 23, 24) for supplying gas-liquid mixture to the degassing chamber (14) are supplied in pairs with flows having identical caustic flow rates, gas flow rates, temperatures and pressures.

11. The deaeration method of any one of claims 8 to 10, wherein, The fastest jets are farthest from the center of the supply pipes and the slowest jets are from the center pair (21, 22) or from the single center supply pipe (24) that is not in a pair.

12. The degassing method of the preceding claim, wherein, The pairs of supply pipes follow a progression whereby jet speed increases from the center pair to the outermost pair.

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