Device for degassing gas-liquid mixture

Abstract

The device comprises:-an inlet (7) for the fluid to be degassed and an outlet (8) for the degassed liquid, which are arranged in the lower part or in one of the side walls of the tank body,-a gas discharge orifice (9) arranged in the upper part of the tank body, and-a conduit (10) for conveying the fluid to be degassed, which conduit is connected to the inlet (7) and comprises an outlet (11), and-an overflow structure (12) arranged in the gas layer and supplied with the fluid to be degassed by the outlet (11). The overflow structure (12) comprises an opening facing the upper portion of the tank, the opening being configured to deliver the fluid by providing gradual degassing as the fluid is delivered from the outlet (11) in order to supply at least partially degassed liquid to the lower portion and gas exiting through the opening to the upper portion.

Description

[0001] The present invention relates to a device for degassing a fluid formed by a gas-liquid mixture.

[0002] In many fields, the ability to separate liquids and gases is essential.

[0003] The degassing device according to the invention is intended in particular for use in a water electrolysis installation at atmospheric pressure or slightly elevated pressure, and is intended for the industrial production of hydrogen and / or oxygen.

[0004] Industrial pressurized water electrolysis installations such as those described in French Patent No. 1,151,507 use a degasser connected to the anode electrolyte outlet of the electrolyzer and a degasser connected to the cathode electrolyte outlet. The first of these degassers extracts oxygen bubbles from the electrolyte liquid leaving the electrolyzer on the anode chamber side, and the second of these degassers extracts hydrogen bubbles from the electrolyte liquid leaving the electrolyzer on the cathode chamber side.

[0005] The degassed electrolyte liquid leaving these two degassers is then remixed and the resulting mixture is reinjected into the electrolyzer. Thus, the electrolyte liquid continuously circulates in a closed loop in the electrolysis installation, the flow rate of which is mainly related to the cooling of the electrolyzer. The degassers need to be sufficiently degassed to achieve maximum efficiency. The aim is to prevent hydrogen from escaping into the oxygen and vice versa. Generally, hydrogen in the oxygen stream escapes into the atmosphere, and oxygen in the hydrogen stream recombines with the escaping hydrogen to form water. The result is a direct production loss. Additionally, when the degassed liquids are remixed, deep degassing prevents the formation of even the slightest amount of a dangerous explosive mixture of hydrogen-oxygen bubbles.

[0006] These degassers operate on the principle of degassing by allowing the bubbles to gradually rise to the liquid surface. Degassing involves introducing the liquid containing the bubbles into a container where a liquid-gas interface is formed and waiting for the bubbles to rise to the interface. The bubbles are then trapped by the gas volume above the interface and are no longer able to re-enter the liquid volume below the interface. The longer the liquid to be degassed remains in the degasser, the larger the liquid-gas interface, and the better the degassing effect.

[0007] In the case of an electrolysis installation as defined above, the electrolyte liquid continuously circulates at a preferably constant flow rate and thus does not remain in the degasser. To achieve more efficient degassing, the liquid flow rate in the degasser is reduced as much as possible by increasing the cross-sectional area of the degasser, and the liquid-gas interface is increased as much as possible. This results in an oversized degasser.

[0008] This poses the problem of providing an improved degassing device that does not have the disadvantages mentioned above.

[0009] The solution of the present invention is a device for degassing a fluid formed by a gas-liquid mixture, the device comprising: a tank including an elongated tank body 1 along axis XX, the elongated tank body including a lower part 2 forming a bottom, an upper part 3 forming a top, and a side wall 4 connecting the lower part and the upper part so as to form an internal volume therebetween, the internal volume being configured to accommodate at least a partially degassed liquid 5 in the lower part and a gas layer 6 in the upper part, wherein:

[0010] - An inlet 7 for the fluid to be degassed and an outlet 8 for the degassed liquid are arranged in the lower part of the tank body or in one of the side walls,

[0011] - A gas discharge orifice 9 is arranged in the upper part of the tank body, and

[0012] - The internal volume of the tank body includes:

[0013] - A conduit 10 for conveying the fluid to be degassed, the conduit being fluidly connected to the inlet 7 for the fluid to be degassed and including a conduit outlet 11 leading to the gas layer, and

[0014] - An elongated overflow structure 12, the elongated overflow structure being arranged in the gas layer, extending along axis XX in the tank body and being supplied with degassed fluid via the conduit outlet 11 of the conduit 10 for conveying the degassed fluid,

[0015] And wherein the overflow structure 12:

[0016] - Includes at least one opening facing the upper part of the tank, and

[0017] - Is configured to convey the fluid to be degassed, thereby ensuring that the fluid is gradually degassed when being conveyed from the conduit outlet 11 of the conduit for conveying the fluid to be degassed, so as to supply at least a partially degassed liquid to the lower part of the tank body and supply gas escaping through the opening to the upper part of the tank body.

[0018] In the tank body, the gas layer 6 is located above the liquid 5.

[0019] Figure 1 Figure 1 is a view of the device according to the present invention

[0020] Optionally, the device according to the present invention may have one or more of the following features:

[0021] - The device includes a gas cleaning device arranged above the gas discharge orifice 9; - The cleaning device prevents entrainment of liquid droplets;

[0022] - Tank 1 is a horizontal tank;

[0023] - The overflow structure 12 includes a bottom defined by two side walls and is preferably shaped like a trough; preferably, the inclination angle of the overflow structure with respect to the horizontal plane is between 0° and -2°

[0024] between

[0025] - The opening of the overflow structure 12 extends along the entire length of the structure;

[0026] - The overflow structure 12 includes an upper part that forms a top parallel to the bottom defined by the side walls and has a number of openings facing the upper part of the tank and distributed along the entire length of the structure;

[0027] - The XX axis is horizontal;

[0028] - The overflow structure 12 is arranged in the upper part of the tank, preferably in the upper quarter part of the tank;

[0029] - The degassed liquid occupies between 50% and 90% of the internal volume, preferably between 50% and 75% of the internal volume.

[0030] - The length of the overflow structure is between 70% and 95% of the length of the tank, preferably between 85% and 90%. However, it is important that the length of the overflow structure is not too large to avoid liquid spreading into the gas / liquid interface of the tank structure and causing eddies in the liquid phase. These eddy motions disperse a large number of microbubbles in the liquid phase, resulting in an excessive gas content in the liquid withdrawn from the tank structure.

[0031] - The overflow structure 12 includes a first end and a second end. The first end is connected to the conduit for delivering the fluid to be degassed, the second end corresponds to the position where the lower part of the tank body is supplied with the degassed liquid, and the gas discharge orifice is arranged closer to the second end than the first end.

[0032] - The overflow structure 12 is arranged at the interface between the at least partially degassed liquid volume and the gas layer.

[0033] - The conduit for delivering the fluid to be degassed is arranged vertically or at a small angle towards the gas / liquid interface to allow the degassed liquid to slowly penetrate into the gas / liquid interface along the overflow structure.

[0034] - Tank 1 is a closed cylinder at both ends.

[0035] - The overflow structure 12 is between 70% and 90% of the length of the tank.

[0036] The present invention enables bubbles to be separated from the liquid to be degassed more quickly. In fact, the overflow structure allows the liquid to be degassed with a very low conveying liquid level, which is beneficial for the gradual separation of bubbles and thus beneficial for the initial degassing of the fluid to be degassed. For example, the height of the liquid to be degassed in the overflow structure is between 10% and 2% of the height of the degassed liquid volume, preferably between 5% and 3% of the height of the degassed liquid volume. The second degassing process occurs naturally in the lower part of the tank, and the bubbles rise at the interface between the at least partially degassed liquid volume and the gas layer. Finally, since the overflow structure allows the at least partially degassed liquid to flow more smoothly into the lower part of the tank containing the at least partially degassed liquid, less turbulence is observed. In fact, with the use of the overflow structure, the chance of the liquid falling into the gas-liquid interface is very small, which may cause the formation of eddies and bubbles at the bottom of the liquid phase, as well as a splashing effect. In this way, the liquid near the outlet of the degassed liquid will contain less than 99.9% gas, preferably less than 99.95% gas. When comparing the degassing device according to the present invention with a degassing device similar to the device according to the present invention and having a similar capacity but neither including an internal conduit nor an overflow structure, an increase in the degassing rate between 300% and 50% is observed, preferably between 300% and 200%.

[0037] Furthermore, by placing the overflow structure at the interface between the gas layer and the at least partially degassed liquid volume, and preferably by immersing the end of the overflow structure opposite the internal conduit in the degassed liquid volume, the turbulence in the degassed liquid volume and any possible entrainment of bubbles in the lower part of the tank body are minimized.

[0038] Therefore, due to the greatly improved gas / liquid distribution, it is no longer necessary to oversize the degassing device, which is very beneficial in terms of floor area, manufacturing requirements, and HSE risks after gas separation, because the volume concentration in the device will be lower.

[0039] Another object of the present invention is to use the device according to the present invention to degas a liquid containing between 25% and 90% gas, preferably between 30% and 50% gas.

[0040] In particular, the device according to the present invention can be used to degas the electrolyte liquid downstream of one or more electrolytic cells. To achieve this, two degassing devices will be used, one degassing device for extracting hydrogen bubbles and the other degassing device for extracting oxygen bubbles.

[0041] Even more particularly, the present invention will be applied to facilities with less equipment.

[0042] Therefore, a further object of the present invention is a hydrogen production facility, comprising:

[0043] - n electrolyzers connected in series, where n > 1, the n electrolyzers connected in series being configured to electrolyze water and produce a hydrogen-liquid mixture, the n electrolyzers connected in series preferably having a total capacity of more than 40 MW,

[0044] - at least one degassing device according to the present invention, the at least one degassing device being configured to remove the liquid contained in the hydrogen-liquid mixture produced by the n electrolyzers connected in series and / or remove the liquid contained in the oxygen-liquid mixture produced by the n electrolyzers connected in series, and to produce a hydrogen stream and an oxygen stream,

[0045] - means for recovering the hydrogen stream, and

[0046] - means for recovering the liquid stream.

[0047] In other words, in the installation according to the present invention, a single degassing device configured to remove the liquid contained in the hydrogen-liquid mixture is associated with the n water electrolysis modules.

[0048] "Liquid" means the electrolyte liquid as mentioned above, which is water that may contain up to about 40% by mass of salt; the salt is preferably potassium hydroxide.

[0049] Preferably, each electrolyzer is composed of a number of electrolytic cell stacks connected in series, most likely of the alkaline or PEM (proton exchange membrane) type, this structure is usually called a stack. The stack is supplied with direct current by a power distribution system with adjustable output voltage. Other types of electrolytic cells can be used, such as AEM cells (anion exchange membrane cells), SOEC (solid oxide electrolytic cells) and PCEC (proton ceramic electrochemical cells). More generally, any type of electrolyzer can be used.

[0050] The "total capacity" of the n electrolyzers connected in series is understood as the sum of the n capacities of the n electrolyzers.

[0051] Preferably, the n water electrolysis modules connected in series will have a total capacity of more than 100 MW or even more than several hundred MW.

[0052] Generally, for an electrolysis capacity of about 5 MW per stack, "n" can be between 8 and 200, preferably between 16 and 40.

[0053] The term "pipeline" means a set of conduits, pumps and valves.

[0054] It goes without saying that, in addition to hydrogen, the series of n water electrolysis modules also produces oxygen. Advantageously, the facility will include a second degassing device according to the present invention, which is configured to remove the aqueous solution (or water containing up to about 40% by mass of salt) contained in the oxygen-liquid solution mixture produced by the series of n electrolytic cells. There will also be n pipelines 13, which are configured to supply the oxygen-liquid mixture produced by the n electrolytic cells to the second degassing device 14. Then, the oxygen 15 recovered at the outlet of the second degassing device will be cooled to a temperature between 30°C and 40°C in the cooler 16 and then collected in the collection system 19, or more generally will be sent to the atmosphere.

[0055] Water can be stored in a storage tank connected to the water supply circuit upstream of the series of n electrolytic cells. The water supply circuit can be connected to running water and includes several water purification units, which can be of different types (such as resins and / or activated carbon) for improving purification. For example, a conductivity sensor installed in the water supply circuit allows continuous monitoring of the water purity level. Analyzers can also be used to monitor the salt impurity level in the purified water.

[0056] The facility according to the present invention can include a circuit for recirculating the liquid between the degassing device and the series of n electrolytic cells. Advantageously, each recirculation circuit will include a cooler to cool the liquid to a temperature lower than the temperature of the electrolytic cell, preferably to a temperature between 50°C and 80°C, and even more preferably to a temperature between 60°C and 70°C.

[0057] Depending on the situation, the device according to the present invention can have one or more of the following characteristics:

[0058] - The degassing device 8 is connected to a capacity greater than 40 MW, preferably greater than 100 MW;

[0059] - The degassing device 8 has a hydrogen inventory H less than or equal to 0.7nh, where:

[0060] - n is the number of electrolytic cells, and

[0061] - h is the hydrogen inventory in each degassing device configured to remove the liquid contained in the hydrogen-liquid mixture for a facility with a capacity similar to that of the facility according to the present invention and including n electrolytic cells associated in series with n degassing devices configured to remove the liquid contained in the hydrogen-liquid mixture;

[0062] "Inventory" refers to the volume of hydrogen accumulated in the degassing device; it is usually expressed in m 3 (cubic meters)

[0063] - The degassing device 8 is made of a material selected from carbon steel, stainless steel, duplex steel, nickel, electroless nickel or nickel-plated carbon

[0064] steel.

[0065] - The series of n electrolytic cells 4 are housed in at least one enclosed building B, and the degassing

[0066] device 8 is located outside the building B, thereby reducing the size of the building B;

[0067] - The pipeline 7 (and preferably the associated valves) is at least mostly located outside the building B;

[0068] This also reduces the size of the building B and limits the risk of hydrogen leakage into the building B.

[0069] In addition, placing the valves outside the building B also makes them more accessible.

[0070] - The facility includes a cooler 10 which is configured to cool the hydrogen gas 9 leaving the degassing device 8; - In other words, a single cooler is associated with a single degassing device 8; - The cooler

[0071] can be a thermoelectric gas cooler, but more generally a plate exchanger or a tube exchanger. - The facility includes a purification unit 11 for purifying the hydrogen gas stream leaving the cooler 10; The impurities to be removed are mainly oxygen and water, as well as some trace salts. The purification unit 11 can be selected from:

[0072] a water washing unit for removing salts (such as potassium hydroxide), a cooler which may or may not be connected to the water washing unit and cools the stream to a temperature between 30°C and 40°C, a catalytic deoxygenation unit and a drying unit (such as a drying cooler or a molecular sieve drying which cools the stream to a temperature between 5°C and 10°C). Preferably, these different units will be added to the facility in series. Note that the water recovered at the end of drying can be recycled in the series of n electrolytic cells. An analysis unit can be placed downstream of the purification unit(s) to check the residual concentration of impurities in the hydrogen gas stream.

[0073] - The facility includes a hydrogen gas stream compression unit located downstream of the purification unit 11. The type of compressor can be reciprocating, centrifugal or mainly diaphragm type; Note that the compression unit can also be placed upstream of the purification unit 11;

[0074] - The facility includes a static mixer which is configured to mix the hydrogen gas from n pipelines upstream of the gas-liquid separation device.

[0075] - The facility includes a hydrogen gas stream compression unit located downstream of the purification unit 11. The type of compressor can be reciprocating, centrifugal or mainly diaphragm type; Note that the compression unit can also be placed upstream of the purification unit 11;

[0076] - The facility includes a static mixer which is configured to mix the hydrogen gas from n pipelines upstream of the gas-liquid separation device.

[0077] The static mixer ensures a uniform bubble size, thus contributing to the separation in the gas-liquid separation device.

[0078] Figure 2 Now, this facility according to the present invention will be described in more detail with the aid of Figure 2 more detailed description.

[0079] Water 1 from the supply or storage tank 2 is introduced into the water treatment unit 3 ( "water treatment" is preferably understood to mean demineralization and deionization). Then the purified water is injected into the liquid circuit for subsequent electrolysis in n electrolytic cells 4 (stacks) connected in series, and the total capacity of the n electrolytic cells connected in series is greater than 40 MW. When leaving the n electrolytic cells 4 connected in series, a hydrogen-liquid mixture 5 and an oxygen-liquid mixture 6 are recovered. The hydrogen-liquid mixture 5 is supplied to a first degassing device 8 via n pipelines 7, and the first degassing device is configured to remove the liquid contained in the hydrogen-liquid mixture generated by the n electrolytic cells 4 connected in series. The hydrogen stream 9 leaving the degassing device 8 is saturated with water. The hydrogen stream 9 is usually cooled to a temperature between 40 °C and 30 °C in a cooler 10 before being introduced into the purification unit 11. The hydrogen stream 12 leaving the purification unit 11 has a purity greater than 99.99%, preferably greater than 99.999%. Before being stored 18 or supplied to the extraction circuit, the hydrogen stream 12 can optionally be compressed to a pressure greater than the pressure entering the purification unit 11, preferably greater than 15 bar.

[0080] Meanwhile, the oxygen-liquid mixture 6 is supplied to a second degassing device 14 via n pipelines 13, and the second degassing device is configured to remove the liquid contained in the oxygen-liquid mixture 6 generated by the n electrolytic cells 4 connected in series. The oxygen stream 15 leaving the second degassing device 14 is saturated with water. The oxygen stream 15 is cooled to a temperature between 40 °C and 30 °C in a cooler 16. The oxygen stream 17 leaving the cooler 16 has a purity greater than 98%, preferably greater than 99%; the oxygen stream is stored in a collection system 19 or conveyed towards the extraction circuit.

[0081] The facility according to the present invention does not include the "n" gas-liquid separation devices configured to remove the liquid contained in the hydrogen-liquid mixture generated by the n electrolytic cells 4 connected in series as proposed in the prior art, but includes a single gas-liquid separation device 8 configured to remove the liquid contained in the hydrogen-liquid mixture 5 generated by the n electrolytic cells 4 connected in series.

[0082] In other words, the facility according to the present invention implementing the degassing device enables:

[0083] - reducing the number of devices;

[0084] ​- Limit HSE (Health - Safety - Environment) risks by reducing the hydrogen storage devices;

[0085] - Reduce the size of the facility and the required floor area. In fact, by reducing the number of equipment, the safety distance is also reduced; and

[0086] - Lower the installation cost.

[0087] -

Claims

1. An apparatus for degassing a fluid formed by a gas-liquid mixture, the apparatus comprising: A tank, said tank comprising an elongate tank body (1) along axis XX, said elongate tank body including a lower part (2) forming a bottom, an upper part (3) forming a top, and a side wall (4) connecting said lower part and said upper part so as to form an internal volume therebetween, said internal volume being configured to accommodate at least partially degassed liquid (5) in said lower part and a gas layer (6) in said upper part, wherein: - An inlet (7) for said fluid to be degassed and an outlet (8) for the degassed liquid are arranged in said lower part of said tank body or in one of the side walls of said side wall, - A gas discharge orifice (9) is arranged in said upper part of said tank body, and - Said internal volume of said tank body includes: - A conduit (10) for conveying said fluid to be degassed, said conduit being fluidly connected to said inlet (7) for said fluid to be degassed and including a conduit outlet (11) leading to said gas layer, and - An elongate overflow structure (12), said elongate overflow structure being arranged in said gas layer, extending along axis XX in said tank body and supplied with degassed fluid via said conduit outlet (11) of said conduit 10 for conveying degassed fluid, and wherein said overflow structure (12): - Includes at least one opening facing said upper part of said tank, and - Is configured to convey said fluid to be degassed so as to ensure that said fluid is gradually degassed when being conveyed from said conduit outlet (11) for conveying said fluid to be degassed, so as to supply at least partially degassed liquid to said lower part of said tank body and supply gas escaping through said opening to said upper part of said tank body.

2. The device according to claim 1, characterized in that Said overflow structure (12) includes a bottom defined by two side walls and preferably has the shape of a trough.

3. The device according to claim 2, characterized in that Said overflow structure (12) includes an upper part, said upper part forming a top parallel to said bottom defined by said side walls and having a plurality of openings facing said upper part of said tank and distributed along the entire length of said structure.

4. The device according to any one of claims 1 to 3, characterized in that The openings of said overflow structure (12) extend along the entire length of said structure.

5. The device according to any one of claims 1 to 4, characterized in that Said axis XX is horizontal.

6. The device according to any one of claims 1 to 5, characterized in that Said overflow structure (12) is arranged in said upper part of said tank, preferably arranged in the upper quarter part of said tank.

7. The device according to any one of claims 1 to 6, characterized in that Said degassed liquid occupies between 50% and 90% of said internal volume, preferably between 50% and 75% of said internal volume.

8. The device according to any one of claims 1 to 7, characterized in that The length of said overflow structure is between 70% and 95% of the length of said tank, preferably between 85% and 90%.

9. The device according to any one of claims 1 to 8, characterized in that Said overflow structure (12) includes a first end and a second end, said first end being connected to said conduit for conveying said fluid to be degassed, said second end corresponding to the position where said lower part of said tank body is supplied with degassed liquid, and said gas discharge orifice is arranged closer to said second end than to said first end.

10. The device according to any one of claims 1 to 9, characterized in that The overflow structure is arranged at the interface between the degassed liquid volume and the gas layer.

11. The device according to any one of claims 1 to 10, characterized in that The conduit for conveying the fluid to be degassed is arranged vertically.

12. The device according to any one of claims 1 to 11, characterized in that The tank is a cylinder closed at both ends.

13. The device according to any one of claims 1 to 12, characterized in that The length of the overflow structure is between 70% and 90% of the length of the tank.

14. Use of the device according to any one of claims 1 to 13 for degassing a liquid containing between 25% and 90% gas, preferably between 30% and 50% gas.

15. A facility for producing hydrogen, comprising: - n electrolytic cells connected in series, where n > 1, the n electrolytic cells connected in series being configured to electrolyze water and produce a hydrogen-liquid mixture, the n electrolytic cells connected in series preferably having a total capacity of more than 40 MW, - at least one degassing device according to any one of the preceding claims, the at least one degassing device being configured to remove the liquid contained in the hydrogen-liquid mixture produced by the n electrolytic cells connected in series and / or to remove the liquid contained in the oxygen-liquid mixture produced by the n electrolytic cells connected in series, and to produce a hydrogen stream and an oxygen stream, - means for recovering the hydrogen stream, and - means for recovering the liquid stream.

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