FR3144019A1 - Device for degassing a gas-liquid mixture - Google Patents

Abstract

Device for degassing a gas-liquid mixture This device comprises: - an inlet (7) for the fluid to be degassed and an outlet (8) for the degassed liquid arranged in a lower part of a tank body or in one of the side walls, - a gas evacuation orifice (9) arranged in the upper part of the tank body, and - a conduit (10) for conveying fluid to be degassed, connected to the inlet (7) and comprising a outlet (11), and - a spillway structure (12) arranged in the gaseous sky, supplied with fluid to be degassed via the outlet (11). The overflow structure (12) comprises an opening facing the upper part of the tank, configured to convey the fluid by ensuring progressive degassing during its conveyance from the outlet (11), to supply the lower part with liquid at least partially degassed and the upper part with gas escaping through the opening. Figure for abstract: 1

Description

Device for degassing a gas-liquid mixture

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

In many areas it is imperative to be able to separate liquids and gases.

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

An industrial installation for electrolysis of water under pressure, 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 side of the anode compartments, and the second of these degassers extracts the Hydrogen gas bubbles from the electrolytic liquid leaving the electrolyzer on the cathode compartments side .

The degassed electrolytic liquids leaving these two degassers are then remixed, and the mixture obtained is reinjected into the electrolyser. 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. Degassers must perform extensive degassing to obtain maximum efficiency. In fact, it is a question of avoiding a loss of hydrogen in oxygen and vice versa. Typically, the hydrogen in the oxygen stream is lost to the atmosphere, and the oxygen in the hydrogen stream is recombined with it, producing water. We are thus witnessing a direct loss of production. Furthermore, extensive degassing also makes it possible to avoid, after remixing the degassed liquids, the formation, even minimal, of a dangerously explosive mixture of Hydrogen and Oxygen gas bubbles.

In these degassers we use the principle of degassing by progressive 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 gaseous volume located above this interface and can no longer reintegrate the volume of liquid located below it. Degassing is therefore more thorough as the liquid to be degassed stays longer in the degasser, and as the liquid-gas interface is larger.

In the case of an electrolysis installation as defined above, the electrolytic liquid circulates continuously at a preferably constant flow rate, and cannot therefore stagnate in the degasser. To obtain extensive 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.

From there, a problem which arises is to provide an improved degassing device, not having the aforementioned drawbacks.

A solution of the present invention is a device for degassing a fluid formed from a gas-liquid mixture comprising a tank comprising an elongated tank body 1 along an axis XX comprising a lower part 3 forming a bottom, an upper part 2 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 sky 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 evacuation port 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, fluidly connected to the inlet 7 of fluid to be degassed, and comprising a conduit outlet 11 opening into the gaseous sky, and

- an overflow structure 12 of elongated shape arranged in the gaseous sky, extending along the axis XX in the tank body and supplied with fluid to be degassed by the conduit outlet 11 of the conveying conduit 10 of 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 conveying conduit 11 of fluid to be degassed, so as to supply the lower part of the tank body with liquid at least partially degassed and the upper part of the tank body with gas escaping through the opening.

In the tank body, said gaseous sky 6 overcomes the liquid 5.

There is a diagram of the device according to the invention

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

- the device comprises a gas cleaning device arranged above the gas evacuation port 9; this cleaning device prevents the entrainment of microdroplets of liquid;

- tank 1 is a horizontal tank;

- 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 between 0° and -2°C

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

- 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 tank and distributed over the entire length of said structure;

- axis XX is horizontal;

- the spillway structure 12 is arranged in the upper part of the tank, preferably in the upper quarter of the tank;

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

- 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 overflow structure is not too great in order to prevent the liquid which spreads into the gas/liquid interface of the reservoir structure from causing swirling currents within the liquid phase. These swirling movements are likely to disperse significant quantities of microbubbles within the liquid phase and thus an excessively high gas content in the liquid withdrawn from the reservoir structure.

- the overflow structure 12 comprises a first end connected to the conduit for conveying 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 evacuation orifice of the gas is arranged closer to the second end than to the first end.

- the overflow structure 12 is arranged at the interface between the volume of at least partially degassed liquid and the gaseous sky.

- the fluid delivery conduit 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 throughout the overflow structure into the gas/liquid interface.

- tank 1 is a cylinder closed at its ends.

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

The present invention allows faster separation of the gas bubbles included in the liquid to be degassed. Indeed, the overflow structure allows the delivery of a very low level of liquid to be degassed, which facilitates the progressive separation of the gas bubbles and thus an initial degassing of the fluid to be degassed. For example, the height of the liquid to be degassed in the overflow 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 at the interface between the volume of at least partially degassed liquid and the gaseous sky. Finally, the overflow structure allowing 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 overflow structure there is very little chance of liquid falling into the gas-liquid interface which could cause swirls, 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 include less than 99.9% gas, preferably less 99.95% gas. If we compare the degassing device according to the invention with a degassing device degassing similar to the device according to the invention and of similar capacity, but comprising neither an internal conduit nor a spillway structure, an increase in the degasification speed of between 300% and 50%, preferably between 300% and 200% is observed. %.

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

Consequently, the gas/liquid distribution being 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 less.

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.

The device according to the invention could 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.

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

For this reason, the present invention also relates to a hydrogen production installation 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 the invention configured to eliminate the liquid contained in the hydrogen-liquid mixture generated by the series of n electrolysers and/or to eliminate the liquid contained in the oxygen-liquid mixture generated by the series of n electrolyzers, and produce a flow of hydrogen and a flow of oxygen,

- A means of recovering a flow of hydrogen, and

- A means of recovering a flow of liquid.

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.

By liquid, we mean the electrolytic liquid as mentioned previously, which is water which can contain up to approximately 40% by weight of salts; the salts preferably being potassium hydroxide.

Preferably, each electrolyser consists of a stack of several electrolysis cells which can most probably be of the alkaline or PEM type (proton exchange membrane) connected in series, which is commonly called a stack. The stack is supplied with direct current by an electrical distribution system whose output voltage can be adjustable. Other types of electrolysis cells can be used such as AEM cells (anion exchange membrane), SOEC (solid oxide electrolysis cells), PCECs (protonic ceramic electrochemical cells) More generally, any type of electrolyzer can be used.

By “overall capacity” of the series of n electrolysers, we mean the accumulation of the n capacities of the n electrolysers.

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

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

By the term “lines” we mean a set of pipes, pumps and valves.

It goes without saying that the series of n water electrolysis modules generates oxygen in addition to hydrogen. Also advantageously, the installation will include a second degassing device according to the invention configured to eliminate the aqueous solution (or water comprising up to approximately 40% by weight of salts) contained in the oxygen-liquid mixture generated by the series of n electrolysers . We will therefore also have 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 between 30 and 40°C, then collected in a collection system 19 or will more generally be sent to the atmosphere.

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 running water and includes several water purification units, which may be of different type (for example resin and/or activated carbon) for better purification. For example, a conductivity sensor mounted on the water supply circuit makes it possible to continuously check the degree of purity of the water. The use of analyzers can also help monitor the level of salt impurity in purified water.

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

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

- 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 0.7nh with:

- n the number of electrolyzers and,

- 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 degassing configured to eliminate the liquid contained in the hydrogen-liquid mixture;

by “inventory” we mean the volume of hydrogen accumulated in the degassing device; it is generally expressed in m ³ (cubic meter)

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

- 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 building B is thus reduced;

- 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 limit the risks of hydrogen leaks in building B. Furthermore, by placing the valves outside of building B we facilitate their accessibility.

- the installation includes 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 can be a Peltier effect gas cooler, but more generally a plate exchanger or a tubular exchanger.

- The installation includes a purification unit 11 of 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 can be chosen from: a water washing unit making it possible to eliminate the salts (for example the potassium hydroxide), a cooler coupled or not to the water washing unit and making it possible to cool the flow to a temperature between 30 and 40°C, a catalytic deoxygenation unit, and a drying unit ( for example drying by cooling allowing the flow to be cooled to a temperature between 5 and 10°C or drying on a molecular sieve). Preferably, these different units will be added in series to the installation. Note that the water recovered at the drying outlet can be recycled in the series of n electrolysers. An analysis unit could 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 hydrogen flow compression unit downstream of the purification unit 11. The type of compressor can be reciprocating, centrifugal or mainly membrane; Note that a compression unit can also be placed upstream of the purification unit 11;

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

The static mixer allows you to have homogeneous bubble sizes and thus have easier separation in the gas-liquid separation device.

This installation according to the invention will now be described in more detail using the .

Water 1 coming from a supply or a 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 then be electrolyzed in a series of n electrolysers 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 eliminate the liquid contained in the hydrogen-liquid mixture generated by the series of n electrolysers 4. The hydrogen flow 9 leaving the degassing device 8 is saturated with water. The hydrogen flow 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 flow 12 leaving the purification unit 11 presents a purity greater than 99.99%, preferably greater than 99.999%. The hydrogen flow 12 may possibly 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 in an extraction circuit.

The oxygen-liquid mixture 6 for its part is conveyed via n lines 13 to the second degassing device 14 configured to eliminate the liquid contained in the oxygen-liquid mixture 6 generated by the series of n electrolysers 4. The outgoing oxygen flow 15 of 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 routed to an extraction circuit.

The installation according to the invention does not include “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 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 electrolyzers 4.

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

- reduce the number of equipment;

- limit HSE (Hygiene – Safety – Environment) risks by reducing hydrogen accumulating devices;

- reduce the size of the installation and the floor occupancy. Indeed, by reducing the number of equipment, safety distances are also reduced; And

- reduce the cost of installation.

Claims (15)

Device for degassing a fluid formed from a gas-liquid mixture comprising a tank comprising an elongated tank body (1) along an axis XX comprising a lower part (3) forming a bottom, an upper part (2) 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 sky gaseous (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 evacuation port (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, fluidly connected to the inlet (7) for fluid to be degassed, and comprising a conduit outlet (11) opening into the gaseous sky, and
- an overflow structure (12) of elongated shape arranged in the gaseous sky, extending along the axis XX in the tank body and supplied with fluid to be degassed by the conduit outlet (11) of the conveying conduit 10 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 fluid conveying conduit (11) to be degassed, so as to supply the lower part of the tank body with liquid at less partially degassed and the upper part of the tank body with gas escaping through the opening. Device according to claim 1, characterized in that the overflow structure (12) comprises a bottom bordered by two side walls and preferably has the shape of a gutter. 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 tank and distributed over the entire length of said structure. 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. Device according to one of claims 1 to 4, characterized in that the axis XX is horizontal. Device according to one of claims 1 to 5, characterized in that the overflow structure (12) is arranged in the upper part of the tank, preferably in the upper quarter of the tank. 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. 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. Device according to one of claims 1 to 8, characterized in that the overflow structure (12) comprises a first end connected to the conduit for conveying fluid to be degassed and a second end corresponding to the supply point of the lower part of the tank body with degassed liquid, and the gas discharge port is arranged closer to the second end than the first end. Device according to one of claims 1 to 9, characterized in that the overflow structure is arranged at the interface between the volume of degassed liquid and the gaseous sky. Device according to one of claims 1 to 10, characterized in that the fluid delivery conduit to be degassed is arranged vertically. Device according to one of claims 1 to 11, characterized in that the reservoir is a cylinder closed at its ends. Device according to one of claims 1 to 12, characterized in that the overflow structure has a length of between 70% and 90% of the length of the tank. 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. Hydrogen production installation including:
- 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 eliminate the liquid contained in the hydrogen-liquid mixture generated by the series of n electrolysers and/or to eliminate the liquid contained in the oxygen-liquid mixture generated by the series of n electrolyzers, and produce a flow of hydrogen and a flow of oxygen,
- A means of recovering a flow of hydrogen, and
- A means of recovering a flow of liquid.