LIQUID GAS STORAGE TANK

Description

[0001] The invention relates to a storage tank for liquefied gas, in particular liquefied hydrogen.

[0002] US2013 / 008185A1 discloses such a tank.

[0003] The invention relates more particularly to a liquefied gas storage tank, in particular liquefied hydrogen, comprising a shell delimiting a storage volume extending along a principal direction which is horizontal in the tank's operating configuration, the tank comprising at least one deflecting wall in the storage volume.

[0004] Liquid hydrogen is preferred when large quantities of the product need to be stored or transported over long distances. Another advantage of liquid hydrogen is that at a temperature of 20 K, it effectively eliminates all impurities (which are solid at this temperature) from the gas, thus optimizing the performance of fuel cells that use it.

[0005] However, the liquid's low density compared to water, for example, limits the available pressure per hydrostatic head, and the low temperature can lead to significant evaporation losses during transfers. Truck unloading systems and hydrogen refueling station tanks can generate losses of up to 15% of production.

[0006] These losses due to truck pressurization can, of course, be lost at each station or recovered, reheated, recompressed, and reinjected into a liquefier. This requires investing in a loss recirculation system and oversizing the liquefaction system.

[0007] Transporting a subcooled liquid requires precautions to prevent the tank pressure from dropping below atmospheric pressure. This can be dangerous for the tank's mechanical integrity or due to the potential entry of air into the transported fluid.

[0008] Trucks arriving from the liquefier must be pressurized to unload the liquid hydrogen from the truck to the station's storage tank (this tank is generally kept under pressure to ensure the operation of the liquid pump or to allow for the pressurized supply of hydrogen). This pressurization is achieved by evaporating and heating the hydrogen from the truck (PBU). This process therefore injects energy into the truck.

[0009] Once the required quantity of liquid has been transferred to the user, the truck can either refill at another station or return to the liquefier. The truck's movement will reduce the pressure due to the movement of the liquid within the storage volume and its contact with the vapor phase. However, the resulting pressure will always be higher than the initial pressure due to the energy added to the system.

[0010] Ultimately, the number of truck refills and the pressure required at these stations will determine the amount of hydrogen lost or that needs to be re-liquefied at the liquefier after the run. During the depressurization of a cryogenic liquid storage system to another piece of equipment, several scenarios can occur. For example, the pressure reduction inside the storage system generates evaporation of the liquid (bubbles in the liquid) if it is in equilibrium with the vapor. This evaporation tends to homogenize the liquid temperature (anti-stratification). The mass of liquid to be extracted from the storage system to reduce the pressure is directly related to the temperature of the vapor exiting the storage system (the colder the vapor, the higher its density, and the greater the mass to be extracted for the same pressure change).

[0011] When pressurizing a cryogenic liquid storage tank using thermal inlets or from another tank, several scenarios can occur. The pressure inside the tank increases more rapidly as vapor stratifies above the liquid (reducing vapor density as temperature increases). To achieve the same pressure increase, a greater mass of cold vapor (at equilibrium temperature) must be injected than the mass of "hot" vapor, relative to the gas density.

[0012] When filling a cryogenic liquid storage tank with liquid from another reservoir, different scenarios can occur. For example, when filling the tank from the bottom without vapor extraction from the top, the pressure increases more rapidly the more vapor is stratified above the liquid. When filling the tank from the top (rain), the pressure drops more rapidly the colder the liquid is compared to the vapor present in the tank.

[0013] Several scenarios can occur when emptying a cryogenic liquid storage tank. For example, when emptying the tank from the top without adding steam, the pressure drops more rapidly the further the liquid is from equilibrium (subcooled); otherwise, evaporation occurs, as in the case of depressurization.

[0014] When emptying the storage tank with steam added from the top, the mass of steam to be added decreases as the steam temperature is further from equilibrium.

[0015] In summary, the ideal configurations of the vapor (gaseous phase) and the liquid in the tank can change for each operation (depressurization, filling...) and can be summarized as follows.

[0016] Depressurization: stratified vapor, subcooled liquid. Filling: stratified vapor, subcooled liquid. Storage / transport when full: unstratified vapor, subcooled liquid.

[0017] Intermediate storage / transport / vacuum: stratified vapor, subcooled liquid.

[0018] Pressurization: stratified steam, subcooled liquid. Draining: stratified steam, subcooled liquid.

[0019] Therefore, only the storage and / or transport of a full tank would require equilibrium (non-stratified) vapor phase to avoid a significant pressure increase in this small volume of vapor. It is therefore preferable for the liquid to be stratified and subcooled relative to its equilibrium temperature at storage pressure.

[0020] One aim of the present invention is to overcome all or part of the disadvantages of the prior art noted above.

[0021] To this end, the tank according to the invention, which otherwise conforms to the generic definition given in the preamble above, is essentially characterized in that it comprises several deflecting walls within the storage volume, extending in a staggered fashion along the principal direction to force the fluid to make at least one round trip along the principal direction during its transit between the lower and upper ends of the storage volume. This structure makes it possible to maintain the temperature of the stratified and subcooled liquid despite potential movements of the liquid due to transport, natural convection, or filling / emptying operations.

[0022] Furthermore, embodiments of the invention may include one or more of the following characteristics: The deflecting walls extend over a portion of the storage volume in the principal direction from one end of the shell; the deflecting walls are horizontal or substantially horizontal in the tank's operating configuration; the deflecting walls extend horizontally across the entire cross-section of the storage volume; the tank has an odd number of deflecting walls, including three deflecting walls; the tank has a filling and / or withdrawal port located at the lower part of a longitudinal end of the shell; the tank has a filling and / or withdrawal port located at the upper part of a longitudinal end of the shell; the tank has a fluid filling or withdrawal port located at a longitudinal end and at an intermediate height between the upper and lower parts of the storage volume.The tank comprises a deflector wall perforated with a plurality of openings; the tank comprises a deflector wall perforated with a plurality of openings, for example, on only a part of the surface of said deflector wall; the deflector wall located in the upper part of the storage volume is perforated with a plurality of openings; at least a part of the deflector walls is composed of a flexible material, in particular one lighter than the material constituting the casing.

[0023] The invention may also relate to any alternative device or method comprising any combination of the above or below features within the scope of the claims.

[0024] Other features and advantages will become apparent upon reading the description below, which refers to the figures in which: [ Fig. 1 ] represents a schematic and partial vertical cross-sectional view, illustrating a first example of the embodiment of a tank according to the invention, [ Fig. 2 ] represents a schematic and partial vertical cross-sectional view, illustrating a second example of an embodiment of a tank according to the invention, [ Fig. 3 ] represents a schematic and partial vertical cross-sectional view, illustrating a third example of the embodiment of a tank according to the invention.

[0025] Tank 1 shown schematically is configured for the storage of liquefied gas, in particular liquefied hydrogen.

[0026] This tank comprises a casing 2, for example, generally cylindrical in shape, delimiting a storage volume extending along a principal direction A. For example, this principal direction A is the longitudinal direction of the tank. The generatrices of the cylindrical portion may be parallel to this axis or principal direction A. The principal direction A may be horizontal in the tank 1's operating configuration. That is to say, tank 1 may be a "horizontal" or "vertical" or spherical type tank (in the latter case, the principal direction A may be horizontal) or any other suitable shape.

[0027] In the schematic representations, only shell 2 is shown. Of course, tank 1 can be of the double-walled type with a wall arranged around shell 2, creating a vacuum space and providing thermal insulation.

[0028] Tank 1 includes several horizontal baffle walls 3 within the storage volume, extending in a staggered fashion along the main direction A. These baffle walls 3 are arranged to force the fluid to make at least one round trip along the main direction A during its transit between the lower and upper ends of the storage volume 2.

[0029] In the illustrated examples, three deflecting walls are provided. Of course, two or more than three walls can be provided.

[0030] The 3 deflecting walls extend over part of the length of the storage volume from one longitudinal end of the envelope 2. For example, the 3 deflecting walls taken successively vertically are connected alternately to one and then the other longitudinal end of the envelope 2.

[0031] In the case of three baffle walls as illustrated, this forms three baffles forcing the fluid to make three changes of direction longitudinally to pass from top to bottom of the tank (or vice versa).

[0032] Preferably, the 3 deflector walls extend horizontally over the entire section of the storage volume and are connected to the envelope on their lateral edge (except at the so-called free end which forms a vertical passage for the fluid).

[0033] These 3 baffle walls limit the contact or transfer of liquid from the bottom of the storage volume with the liquid or vapor from the top of the storage volume.

[0034] This allows for the maintenance of a stratified and subcooled liquid in the lower part of the storage volume. Depending on the fill level, the vapor can also be stratified or not, depending on the desired benefits.

[0035] As illustrated in [ Fig. 2 ] And [ Fig. 3 ], the tank may have a filling or emptying port 4 located in the lower part of a longitudinal end of the casing 2 and connected to a pipe.

[0036] Similarly, the tank may include a filling or emptying port 5 located at the top of a longitudinal end of the casing 2 and connected to a pipe.

[0037] In bottom-filling systems, the cold liquid entering through port 4 must travel the length of the storage volume before it can reach the next level, and so on. The liquid heats up and partially evaporates if the walls of the casing 2 are too hot. Conversely, this vapor or near-equilibrium liquid is pushed upwards through the storage volume by the horizontal deflector walls without interacting with the cold liquid entering through the feed.

[0038] The steam exiting the storage is heated as it rises in the storage by contact with the hot walls (cooling).

[0039] When the storage volume is full, the stratification of the liquid is maintained with the deflecting walls and it is possible to limit the stratification of the vapor with movements (for transport) or by extraction of the vapor for fixed storage.

[0040] This solution also allows, where applicable, for the advantageous replacement of the "anti-sloshing" liquid baffles traditionally installed in mobile tanks. Indeed, limiting the mass of liquid that can move, thanks to the three deflector walls, automatically reduces the sloshing effect of the liquid during sudden movements. As illustrated in the Fig. 2 ] or to the [ Fig. 3 ], it is possible to provide for a return of fluid, preferably vapor, to the interior of the storage volume via an orifice 6 located at an intermediate height between the upper and lower parts of the storage volume.

[0041] This intermediate orifice 6 can be connected to a pipe and can be located between two deflecting walls 3 in order to allow this fluid and partially this vapor to pass through the liquid for the purpose of its condensation, while keeping part of the liquid subcooled in the lower part.

[0042] In addition, or alternatively, and as illustrated in the [ Fig. 3The last deflector wall (upper) can have a perforated structure (multiple holes) to allow gas to pass through and increase the contact surface between the gas and the liquid. This option can also be advantageously used when filling the storage volume from the top to increase the exchange areas between the incoming (falling) liquid and the existing gas. This eliminates the need for an injector-type liquid distributor along the length of the tank.

[0043] In addition, or alternatively, the three baffle walls can be made of a lightweight and flexible material (for example, lighter than the rest of the tank) that retains its mechanical properties at low temperatures in order to limit the additional mass of these baffle walls within the tank (see, for example, FR2966899A). Indeed, for transport tanks, the tank's mass limits the maximum quantity of product that can be transported.

[0044] The tank according to the invention, thanks to its deflecting walls which are at least partially immersed in the liquid phase, maintains the stratification of the liquid while keeping the liquid at the interface with the gaseous phase in equilibrium with the gaseous phase (typically at a pressure higher than atmospheric pressure). This allows for subcooled liquid layers to be maintained in the lower part of the tank. This is particularly advantageous for a transport tank, especially for transporting subcooled liquid.

Claims

1. A storage tank for liquefied gas, in particular liquefied hydrogen, comprising an envelope (2) delimiting a storage volume extending along a principal direction (A) which is horizontal in the use configuration of the tank (1), the tank (1) comprising several baffle plates (3) in the storage volume which extend in a staggered manner along the principal direction (A) to force the fluid to perform at least one back-and-forth travel along the principal direction (A) during its transit between the lower end and the upper end of the storage volume (2), characterized in that several of these baffle plates (3) are located in the lower half of the storage volume.

2. The storage tank according to claim 1, characterized in that the baffle plates (3) extend over a part of the storage volume along the principal direction (A) from one end of the envelope (2).

3. The storage tank according to claim 1 or 2, characterized in that the baffle plates (3) are horizontal or substantially horizontal in the use configuration of the tank (1).

4. The storage tank according to any one of claims 1 to 3, characterized in that the baffle plates (3) extend horizontally over the entire section of the storage volume.

5. The storage tank according to any one of claims 1 to 4, characterized in that it comprises an odd number of baffle plates (3), in particular three baffle plates (3).

6. The storage tank according to any one of claims 1 to 5, characterized in that it comprises a filling and / or withdrawal orifice (4) located in the lower part of a longitudinal end of the envelope (2).

7. The storage tank according to any one of claims 1 to 6, characterized in that it comprises a filling and / or withdrawal orifice (5) located in the upper part of a longitudinal end of the envelope (2).

8. The storage tank according to any one of claims 1 to 7, characterized in that it comprises a fluid filling or withdrawal orifice (6) located at a longitudinal end and at an intermediate height between the upper and lower parts of the storage volume.

9. The storage tank according to any one of claims 1 to 8, characterized in that it comprises a baffle plate (3) perforated with a plurality of orifices (7).

10. The storage tank according to any one of claims 1 to 9, characterized in that it comprises a baffle plate (3) perforated with a plurality of orifices (7) on only a part of the surface of said baffle plate (3).

11. The storage tank according to any one of claims 1 to 10, characterized in that the baffle plate (3) located in the upper part of the storage volume is perforated with a plurality of orifices (7).

12. The storage tank according to any one of claims 1 to 11, characterized in that at least a part of the baffle plates (3) is made of a flexible material, in particular lighter than the constituent material of the envelope.

13. The storage tank according to any one of claims 1 to 12, characterized in that it contains liquefied gas and at least a part of the baffle plates (3) is immersed in the liquid phase.

14. A method for storing a liquefied cryogenic gas using a tank according to any one of claims 1 to 13, characterized in that the liquefied gas is stored in the tank (1) with a liquid level located above at least one of the baffle plates.