Device for degassing a gas-liquid mixture

Abstract

The invention relates to a device which comprises: - an inlet (7) for the fluid to be degassed and an outlet (8) for the degassed liquid arranged in a lower portion of a tank body or in one of the side walls; - a gas discharge port (9) arranged in the upper portion of the tank body; and - a duct (10) for conveying the fluid to be degassed, connected to the inlet (7) and comprising an outlet (11); and - an overflow structure (12) arranged in the gaseous layer, supplied with fluid to be degassed by the outlet (11). The overflow structure (12) comprises an opening facing the upper portion of the tank, configured to convey the fluid by providing gradual degassing as it is conveyed from the outlet (11), in order to supply the lower portion with at least partially degassed liquid and the upper portion with gas exiting through the opening.

Description

[0001] DESCRIPTION

[0002] TITLE: Device for degassing a gas-liquid mixture

[0003] The present invention relates to a device for degassing a fluid formed from a gas-liquid mixture.

[0004] In many fields it is imperative to be able to separate liquids and gases.

[0005] The degassing device according to the invention is intended to be used in particular in a water electrolysis installation under atmospheric pressure or slightly pressurized and intended for the industrial production of hydrogen and / or oxygen.

[0006] An industrial pressurized water electrolysis installation, for example an installation as described in French patent No. 1,151,507, uses on the one hand a degasser connected to the anolyte outlet of the electrolyzer and on the other hand a degasser connected to the catholyte outlet. The first of these degassers extracts the Oxygen gas bubbles from the electrolytic liquid leaving the electrolyzer on the anode compartment side, and the second of these degassers extracts the Hydrogen gas bubbles from the electrolytic liquid leaving the electrolyzer on the cathode compartment side.

[0007] The degassed electrolytic liquids leaving these two degassers are then remixed, and the resulting mixture is reinjected into the electrolyzer. The electrolytic liquid therefore circulates continuously and in a closed circuit in the electrolysis installation, its flow rate being mainly linked to the cooling of the electrolyzer. The degassers must perform extensive degassing to obtain maximum efficiency. Indeed, the aim is to avoid a loss of hydrogen in the oxygen and vice versa. Generally, the hydrogen in the oxygen flow is lost to the atmosphere, and the oxygen in the hydrogen flow is recombined with it, thus producing water. This results in a direct loss of production. Furthermore, extensive degassing also prevents, after remixing the degassed liquids, the formation, even minimal, of a dangerously explosive mixture of hydrogen and oxygen gas bubbles.

[0008] These degassers use the principle of degassing by the gradual rise of gas bubbles to the surface of the liquid. Degassing consists of introducing the liquid loaded with gas bubbles into a container in which a liquid-gas interface is then created, and waiting for these gas bubbles to rise to this interface. They are then trapped by the gas volume above this interface and can no longer reintegrate the volume of liquid below it. Degassing is therefore all the more thorough the longer the liquid to be degassed remains in the degasser, and the larger the liquid-gas interface.

[0009] In the case of an electrolysis installation as defined above, the electrolytic liquid circulates continuously at a preferably constant flow rate, and therefore cannot stagnate in the degasser. To obtain advanced degassing, the speed of propagation of the liquid in the degasser is reduced as much as possible by increasing its passage section as much as possible, and the liquid-gas interface is increased as much as possible. This therefore leads to oversizing of the degassers.

[0010] From this, a problem arises that is to provide an improved degassing device, which does not have the aforementioned disadvantages.

[0011] A solution of the present invention is a device for degassing a fluid formed from a gas-liquid mixture comprising a reservoir comprising an elongated reservoir body 1 along an axis XX comprising a lower part 2 forming a bottom, an upper part 3 forming a roof, and side walls 4 connecting the lower part and the upper part so as to form between said parts an internal volume, said internal volume being configured to contain liquid 5 at least partially degassed in the lower part and a gaseous canopy 6 in the upper part, in which:

[0012] - 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,

[0013] - a gas discharge orifice 9 is arranged in the upper part of the tank body, and

[0014] - the internal volume of the tank body includes:

[0015] - a conduit 10 for conveying fluid to be degassed, fluidically connected to the inlet 7 for the fluid to be degassed, and comprising a conduit outlet 11 opening into the gaseous air space, and

[0016] - an elongated spillway structure 12 arranged in the gaseous ceiling, extending along the axis XX in the reservoir body and supplied with fluid to be degassed by the conduit outlet 11 of the conduit 10 for conveying fluid to be degassed, and in which said spillway structure 12:

[0017] - includes at least one opening facing the upper part of the tank, and

[0018] - is configured to convey the fluid to be degassed by ensuring progressive degassing of said fluid during its conveyance from the outlet of the conveyance conduit 11 of fluid to be degassed, so as to supply the lower part of the reservoir body with at least partially degassed liquid and the upper part of the reservoir body with gas escaping through the opening. In the reservoir body, said gaseous canopy 6 rises above the liquid 5.

[0019] [Fig 1] Figure 1 is a diagram of the device according to the invention

[0020] Depending on the case, the device according to the invention may have one or more of the characteristics below:

[0021] - the device comprises a gas cleaning device arranged above the gas discharge orifice 9; this cleaning device makes it possible to prevent the entrainment of microdrops of liquid;

[0022] - tank 1 is a horizontal tank;

[0023] - the spillway structure 12 comprises a bottom bordered by two side walls and preferably has the shape of a gutter; preferably the spillway structure has an angle of inclination relative to the horizontal of between 0° and -2°C

[0024] - the opening of the spillway structure 12 extends over the entire length of said structure;

[0025] - the spillway structure 12 comprises an upper part forming a roof parallel to the bottom bordered by the side walls and having several openings facing the upper part of the reservoir and distributed over the entire length of said structure;

[0026] - the XX axis is horizontal;

[0027] - the spillway structure 12 is arranged in the upper part of the reservoir, preferably in the upper quarter of the reservoir;

[0028] - the degassed liquid occupies between 50% and 90% of the internal volume, preferably between 50% and 75% of the internal volume.

[0029] - the length of the spillway structure is between 70% and 95%, preferably between 85% and 90%, of the length of the reservoir. It is nevertheless important that the length of the spillway structure is not too great in order to prevent the liquid spreading in the gas / liquid interface of the reservoir structure from causing swirling currents within the liquid phase. These swirling movements are likely to disperse large quantities of microbubbles within the liquid phase and thus an excessively high gas content in the liquid withdrawn from the reservoir structure.

[0030] - the spillway structure 12 comprises a first end connected to the conduit for conveying the fluid to be degassed and a second end corresponding to the point of supplying the lower part of the tank body with degassed liquid, and the gas discharge orifice is arranged closer to the second end than to the first end.

[0031] - the spillway structure 12 is arranged at the interface between the volume of at least partially degassed liquid and the gaseous atmosphere. - the conduit for conveying the fluid to be degassed is arranged either vertically or slightly inclined towards the gas / liquid interface in order to allow slow penetration of the degassed liquid along the spillway structure into the gas / liquid interface.

[0032] - tank 1 is a cylinder closed at its ends.

[0033] - the spillway structure 12 has a length between 70% and 90% of the length of the reservoir.

[0034] The present invention allows for faster separation of the gas bubbles included in the liquid to be degassed. Indeed, the spillway structure allows for the conveyance of a very low level of liquid to be degassed, which facilitates the progressive separation of the gas bubbles and thus a first degassing of the fluid to be degassed. For example, the height of the liquid to be degassed in the spillway structure represents 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. A second degassing will take place naturally in the lower part of the tank by raising gas bubbles to the interface between the at least partially degassed liquid volume and the gaseous ceiling. Finally, the spillway structure allows for a smoother arrival of the at least partially degassed liquid in the lower part of the tank comprising the at least partially degassed liquid, less turbulence is observed.Indeed, with the spillway structure there is very little chance of having liquid falling into the gas-liquid interface which could cause eddies, entrainment of bubbles at the bottom of the liquid phase but also the splashing effect. In this way, the liquid located near the outlet of the degassed liquid will comprise less than 99.9% gas, preferably less than 99.95% gas. If we compare the degassing device according to the invention with a degassing device similar to the device according to the invention and of similar capacity, but comprising neither an internal conduit nor a spillway structure, we observe an increase in the degasification speed of between 300% and 50%, preferably between 300% and 200%.

[0035] Furthermore, by placing the spillway structure at the interface between the gaseous ceiling and the volume of at least partially degassed liquid, and preferably by immersing the end of said spillway structure opposite the internal conduit in the volume of degassed liquid, turbulence in the volume of degassed liquid and any possible entrainment of gas bubbles in the lower part of the body of the tank are minimized.

[0036] Therefore, since the gas / liquid distribution is greatly improved, it is no longer necessary to oversize the degassing device, which is very beneficial in terms of footprint, manufacturing requirements and also HSE risks depending on the separated gas because the concentration of the volume in said device will be lower. The present invention also relates to the use of the device according to the invention for degassing a liquid comprising between 25% and 90% gas, preferably between 30% and 50% gas.

[0037] The device according to the invention may in particular be used to degas an electrolytic liquid downstream of one or more electrolysers. To do this, two degassing devices according to the invention will be used, one allowing the extraction of hydrogen bubbles, and the other allowing the extraction of oxygen bubbles.

[0038] Even more particularly, the invention will apply to an installation having a reduced number of pieces of equipment.

[0039] For this reason, the present invention also relates to a hydrogen production installation comprising:

[0040] - A series of n electrolysers with n>1 configured to electrolyze water and generate a hydrogen-liquid mixture, preferably said series having an overall capacity greater than 40 MW,

[0041] - At least one degassing device according to the invention configured to remove the liquid contained in the hydrogen-liquid mixture generated by the series of n electrolysers and / or to remove the liquid contained in the oxygen-liquid mixture generated by the series of n electrolysers, and produce a flow of hydrogen and a flow of oxygen,

[0042] - A means of recovering a hydrogen stream, and

[0043] - A means of recovering a flow of liquid.

[0044] In other words, in this installation according to the invention a single degassing device configured to eliminate the liquid contained in the hydrogen-liquid mixture is associated with n water electrolysis modules.

[0045] By liquid we mean the electrolytic liquid as mentioned above, which is water which may comprise up to about 40% by mass of salts; the salts preferably being potassium hydroxide.

[0046] Preferably, each electrolyzer consists of a stack of several electrolysis cells that may most likely be of the alkaline or PEM (proton exchange membrane) type connected in series, commonly called a stack. The stack is powered by direct current by an electrical distribution system whose output voltage can be adjustable. Other types of electrolysis cells may be used, such as AEM (anion exchange membrane) cells, SOEC (solid oxide electrolysis cells), PCEC (proton ceramic electrochemical cell). More generally, any type of electrolyzer may be used. By "total capacity" of the series of n electrolyzers, we mean the sum of the n capacities of the n electrolyzers.

[0047] Preferably, the series of n water electrolysis modules will have an overall capacity greater than 100MW, or even greater than several hundred MW.

[0048] Typically, for an electrolysis capacity of around 5MW per stack, “n” can be between 8 and 200, preferably between 16 and 40.

[0049] The term "lines" means a set of pipes, pumps and valves.

[0050] It goes without saying that the series of n water electrolysis modules generates oxygen in addition to hydrogen. Also advantageously, the installation will comprise a second degassing device according to the invention configured to remove the aqueous solution (or water comprising up to approximately 40% by mass of salts) contained in the oxygen-liquid mixture generated by the series of n electrolysers. There will therefore also be n lines 13 configured to supply the oxygen-liquid mixture generated by the n electrolysers to the second degassing device 14. The oxygen 15 recovered at the outlet of the second degassing device will then be cooled in a cooler 16 to a temperature between 30 and 40°C, then collected in a collection system 19 or will more generally be sent to the atmosphere.

[0051] The water can be stored in a storage tank connected to the water supply circuit upstream of the series of n electrolysers. The water supply circuit can be connected to the running water and includes several water purification units, which can be of different types (e.g. resin and / or activated carbon) for better purification. For example, a conductivity sensor mounted on the water supply circuit allows the degree of purity of the water to be continuously checked. The use of analyzers can also allow the level of salt impurity in the purified water to be monitored.

[0052] The installation according to the invention may comprise liquid recycling loops between the degassing devices and the series of n electrolysers. Advantageously, each recycling loop will comprise a cooler in order to cool the liquid to a temperature lower than that of the electrolysers, preferably to a temperature between 50 and 80°C, even more preferably to a temperature between 60 and 70°C.

[0053] Depending on the case, the installation according to the invention may have one or more of the characteristics below:

[0054] - the degassing device 8 is connected to a capacity greater than 40 MW, preferably greater than 100 MW; - the degassing device 8 has a hydrogen inventory H less than or equal to 0.7 nh with:

[0055] - n the number of electrolysers and,

[0056] - h the hydrogen inventory in each degassing device configured to eliminate the liquid contained in the hydrogen-liquid mixture, for an installation of capacity similar to the installation according to the invention and comprising n electrolysers associated in series with n degassing devices configured to eliminate the liquid contained in the hydrogen-liquid mixture; by "inventory" is meant the volume of hydrogen accumulated in the degassing device; it is generally expressed in m 3 (cubic meter)

[0057] - the degassing device 8 is made of a material chosen from carbon steel, stainless steel, duplex steel, nickel, autocatalytic nickel, or carbon steel with nickel coating.

[0058] - the series of n electrolysers 4 is included in at least one closed building B and the degassing device 8 is located outside this building B; the size of the building B is thus reduced;

[0059] - lines 7, and preferably the associated valves, are located at least largely outside building B; this also makes it possible to reduce the size of building B and to limit the risks of hydrogen leaks in building B. Furthermore, by placing the valves outside building B, their accessibility is facilitated.

[0060] - the installation comprises a cooler 10 configured to cool the hydrogen 9 leaving the degassing device 8; in other words, a single cooler is associated with the single degassing device 8; the cooler may be a Peltier effect gas cooler, but more generally a plate exchanger or a tubular exchanger.

[0061] - The installation comprises a purification unit 11 for the hydrogen flow leaving the cooler 10; The impurities to be eliminated are mainly oxygen and water, as well as some traces of salts... The purification unit 11 may be chosen from: a water washing unit for removing salts (for example potassium hydroxide), a cooler coupled or not to the water washing unit and for cooling the flow to a temperature between 30 and 40°C, a catalytic deoxygenation unit, and a drying unit (for example drying by cooling for cooling the flow to a temperature between 5 and 10°C or drying on molecular sieve). Preferably, these different units will be added in series to the installation. Note that the water recovered at the drying outlet may be recycled in the series of n electrolysers.An analysis unit may be placed downstream of this(these) purification unit(s) in order to check the residual concentration of impurities in the hydrogen flow. - the installation includes a unit for compressing the hydrogen flow downstream of the purification unit 11. The type of compressor may be mainly alternating, centrifugal or membrane; Note that a compression unit may also be placed upstream of the purification unit 11;.

[0062] - the installation includes a static mixer configured to mix hydrogen from the n lines upstream of the gas-liquid separation device.

[0063] The static mixer allows for homogeneous bubble sizes and thus facilitates separation in the gas-liquid separation device.

[0064] [Fig 2] This installation according to the invention will now be described in more detail with the aid of figure 2.

[0065] Water 1 from a supply or storage tank 2 is introduced into a water treatment unit 3 (water treatment preferably means demineralization and deionization). The purified water is then injected into the liquid circuit to be subsequently electrolyzed in a series of n electrolyzers 4 (stacks), said series having an overall capacity greater than 40 MW. Leaving the series of n electrolyzers 4, a hydrogen-liquid mixture 5 and an oxygen-liquid mixture 6 are recovered. The hydrogen-liquid mixture 5 is conveyed via n lines 7 to the first degassing device 8 configured to remove the liquid contained in the hydrogen-liquid mixture generated by the series of n electrolyzers 4. The hydrogen stream 9 leaving the degassing device 8 is saturated with water.The hydrogen stream 9 is generally cooled to a temperature between 40 and 30°C in a cooler 10 before being introduced into a purification unit 11. The hydrogen stream 12 leaving the purification unit 11 has a purity greater than 99.99%, preferably greater than 99.999%. The hydrogen stream 12 may optionally be compressed to a pressure greater than that of entry into the purification unit 11, preferably greater than 15 bar before being stored 18 or conveyed into an extraction circuit.

[0066] The oxygen-liquid mixture 6 is conveyed via n lines 13 to the second degassing device 14 configured to remove the liquid contained in the oxygen-liquid mixture 6 generated by the series of n electrolysers 4. The oxygen flow 15 leaving the second degassing device 14 is saturated with water. The oxygen flow 15 is cooled to a temperature between 40 and 30°C in a cooler 16. The oxygen flow 17 leaving the cooler 16 has a purity greater than 98%, preferably greater than 99%; it will be stored in a collection system 19 or conveyed to an extraction circuit.

[0067] The installation according to the invention does not comprise “n” gas-liquid separation devices configured to eliminate the liquid contained in the hydrogen-liquid mixture generated by the series of n electrolysers 4, as is proposed in the prior art, but comprises a single gas-liquid separation device 8 configured to eliminate the liquid contained in the hydrogen-liquid mixture 5 generated by the series of n electrolysers 4.

[0068] In other words, the installation according to the invention implementing the degassing device makes it possible to:

[0069] - reduce the number of equipment;

[0070] - limit HSE (Health - Safety - Environment) risks by reducing devices that accumulate hydrogen;

[0071] - reduce the size of the installation and the floor space occupied. Indeed, by reducing the number of equipment, the safety distances are also reduced; and

[0072] - reduce the cost of installation.

Claims

CLAIMS 1. Device for degassing a fluid formed from a gas-liquid mixture comprising a reservoir comprising an elongated reservoir body (1) along an axis XX comprising a lower part (2) forming a bottom, an upper part (3) forming a roof, and side walls (4) connecting the lower part and the upper part so as to form an internal volume between said parts, said internal volume being configured to contain liquid (5) at least partially degassed in the lower part and a gaseous canopy (6) in the upper part, in which: - 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, - a gas discharge orifice (9) is arranged in the upper part of the tank body, and - the internal volume of the tank body includes: - a conduit (10) for conveying fluid to be degassed, fluidically connected to the inlet (7) for fluid to be degassed, and comprising a conduit outlet (11) opening into the gaseous air space, and - an elongated spillway structure (12) arranged in the gaseous ceiling, extending along the axis XX in the reservoir body and supplied with fluid to be degassed by the conduit outlet (11) of the conduit 10 for conveying fluid to be degassed, and in which said spillway structure (12): - includes at least one opening facing the upper part of the tank, and - is configured to convey the fluid to be degassed by ensuring progressive degassing of said fluid during its conveyance from the outlet of the conveyance conduit (11) of fluid to be degassed, so as to supply the lower part of the reservoir body with at least partially degassed liquid and the upper part of the reservoir body with gas escaping through the opening.

2. Device according to claim 1, characterized in that the spillway structure (12) comprises a bottom bordered by two side walls and preferably has the shape of a gutter.

3. Device according to claim 2, characterized in that the spillway structure (12) comprises an upper part forming a roof parallel to the bottom bordered by the side walls and having several openings facing the upper part of the reservoir and distributed over the entire length of said structure.

4. Device according to one of claims 1 to 3, characterized in that the opening of the spillway structure (12) extends over the entire length of said structure.

5. Device according to one of claims 1 to 4, characterized in that the axis XX is horizontal.

6. Device according to one of claims 1 to 5, characterized in that the spillway structure (12) is arranged in the upper part of the tank, preferably in the upper quarter of the tank.

7. Device according to one of claims 1 to 6, characterized in that the degassed liquid occupies between 50% and 90% of the internal volume, preferably between 50% and 75% of the internal volume.

8. Device according to one of claims 1 to 7, characterized in that the length of the spillway structure is between 70% and 95%, preferably between 85% and 90%, of the length of the reservoir.

9. Device according to one of claims 1 to 8, characterized in that the spillway structure (12) comprises a first end connected to the conduit for conveying the fluid to be degassed and a second end corresponding to the point of supplying the lower part of the reservoir body with degassed liquid, and the gas discharge orifice is arranged closer to the second end than to the first end.

10. Device according to one of claims 1 to 9, characterized in that the spillway structure is arranged at the interface between the volume of degassed liquid and the gaseous atmosphere.

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

12. Device according to one of claims 1 to 11, characterized in that the reservoir is a cylinder closed at its ends.

13. Device according to one of claims 1 to 12, characterized in that the spillway structure has a length of between 70% and 90% of the length of the reservoir.

14. Use of the device as defined in one of claims 1 to 13 for degassing a liquid comprising between 25% and 90% gas, preferably between 30% and 50% gas.

15. Hydrogen production facility comprising: - A series of n electrolysers with n>1 configured to electrolyze water and generate a hydrogen-liquid mixture, preferably said series having an overall capacity greater than 40 MW, - At least one degassing device according to any one of the preceding claims, configured to remove the liquid contained in the hydrogen-liquid mixture generated by the series of n electrolysers and / or to remove the liquid contained in the oxygen-liquid mixture generated by the series of n electrolysers, and produce a hydrogen flow and an oxygen flow, - A means of recovering a hydrogen stream, and - A means of recovering a flow of liquid.

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