Method for controlling internal pressure of cryogenic tank

Abstract

The present invention relates to a method for controlling the internal pressure of a cryogenic tank (100) containing a liquid fraction (1002) and a gas fraction (1004) of a fluid, the enthalpy of which can be reduced during isothermal compression in the liquid phase.

Description

[Technical Field]

[0001] The present invention relates to the technical field of cryogenic tanks, more particularly to a method for controlling the internal pressure of a cryogenic tank, and also to a facility for storing cryogenic fluids.

[0002] A cryogenic tank is any tank suitable and designed to store gases in liquefied form.

[0003] A cryogenic fluid is any fluid that has been cooled to a temperature below its boiling point. [Background technology]

[0004] The invention is particularly applicable to cryogenic tanks suitable for storing cryogenic fluids at pressures below 20 bar. The pressures given herein and hereinafter are in bar absolute.

[0005] Such tanks are generally used to store cryogenic fluids, which are liquids at atmospheric pressure at temperatures below 273.15 K, in particular below 213.15 K. Typically, these tanks belong to storage facilities.

[0006] These storage facilities are generally configured, on the one hand, to allow the distribution of fluid to one or more demand elements and, on the other hand, to be supplied with fluid from one or more external supply elements.

[0007] For example, demand elements include elements capable of receiving fluid from a tank, which may be, for example, a vehicle configured to receive and store fluid.

[0008] For example, the external supply element may include an element capable of supplying a quantity of fluid in the form of a liquid or gas to the tank.

[0009] In such storage facilities, the cryogenic fluid is initially stored in a liquid state, but inevitably generates boil-off gas, forming a liquid fraction at the bottom of the tank and a gas fraction at the top of the tank. A portion of this gas fraction from the boil-off gas is usually released to the atmosphere without being used. Typically, this release is made possible by protective elements within the tank, such as valves and / or rupture disks, that release at least a portion of the gas fraction to the outside in the event of pressure within the tank exceeding a limit. This limit is typically the maximum allowable pressure of the tank, which limit is usually specified by the manufacturer.

[0010] However, the boil-off gases released into the atmosphere constitute both an ecological and an economic drawback.

[0011] For this reason, various systems and methods have been devised to manage the pressure inside the tank, in order to prevent this boil-off gas from escaping to the outside, which consist either in consuming part of the liquid fraction contained in the tank so as to periodically reduce the internal pressure of the tank, or in extracting part of the gas fraction from the tank and recompressing it through complex and expensive gas compression systems.

[0012] However, for obvious ecological and economic reasons, such a solution cannot be envisaged for commercial use in storage facilities.

[0013] SUMMARY OF THE INVENTION It is therefore an object of the present invention to overcome some or all of the above-identified drawbacks. Summary of the Invention

[0014] To this end, the invention proposes a simple and inexpensive method for controlling the internal pressure of a cryogenic tank and preventing at least part of the gas fraction from escaping from the cryogenic tank as a result of an excessive increase in its internal pressure.

[0015] For this purpose, a method is first proposed for controlling the internal pressure of a cryogenic tank containing a liquid fraction and a gas fraction of a fluid, the enthalpy of which can be reduced during isothermal compression in the liquid phase, the method comprising: - A portion of the liquid fraction is taken out and, at state A, a first temperature T1, - first pressure P1, - the first enthalpy E1, and obtaining a removed portion defined by a first density D1; - compressing the removed portion substantially isothermally to state B; a second temperature T2 substantially equal to the first temperature T1; a second pressure P2 greater than the first pressure P1, and obtaining a compressed part defined by a second density D2 greater than the first density D1, The compression is intended to result in a decrease in enthalpy between a first enthalpy E1 of state A and a second enthalpy E2 of state B; - Expand the compressed part to state C. a third temperature T3 lower than the second temperature T2; a third pressure P3 lower than the second pressure P2, and - obtaining an expanded portion defined by a third density D3, which is smaller than the second density D2 and greater than the first density D1; - injecting the compressed or expanded portion into a storage tank; The expansion is carried out during or after the injection process when the compressed portion is injected into the tank, or The expansion is carried out between the compression and injection steps when the expansion portion is injected into the tank.

[0016] The method according to the invention makes it possible to counteract the increase in the internal pressure of the cryogenic tank caused naturally by the surrounding environment, thus avoiding the release of part of the gas fraction from the tank, for example by activating a safety valve or through the wall of the cryogenic tank.

[0017] Various additional features may be provided singly or in combination. - the compression process results in a continuous decrease in the enthalpy of the extracted part from state A to state B, the compression process is stopped when the enthalpy decrease in the compressed section is less than 0.1 kJ / kg for a pressure increase of 1 bar; -The fluid is hydrogen, the third pressure P3 is greater than or substantially equal to the first pressure P1; The expansion is substantially isenthalpic when carried out between the compression and injection steps.

[0018] Secondly, a facility for storing the liquid and gas fractions of a fluid is proposed, configured to implement the above-mentioned method, said facility comprising: a cryogenic tank intended to contain a fluid; means for removing a portion of the liquid fraction; compression means comprising a compressor element and a cooling element for the compressor element configured to maintain the compressor element at a temperature during compression to achieve a substantially isothermal compression of the withdrawn portion to obtain a compressed portion; - expansion means for expanding the compressed portion to obtain an expanded portion; and an injection means capable of injecting the compressed portion or the expanded portion into the cryogenic tank; The facility may have a combined expansion means and a tank or may be separate.

[0019] The facility according to the invention has the advantage that it is compact and easy to implement, and furthermore it consists only of simple, low-cost components.

[0020] Various additional features may be provided singly or in combination. the facility further comprises a buffer tank disposed between the compression means and the expansion means; The expansion means comprises a throttle valve.

[0021] The invention may also relate to any alternative method or apparatus including any combination of the features set out above or below. [Brief explanation of the drawings]

[0022] Further features and advantages of the present invention will become apparent from a reading of the following detailed description, for the understanding of which reference is made to the accompanying drawings, in which: [Figure 1] 1 is a schematic diagram of a storage facility according to a first embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram of a storage facility according to a second embodiment of the present invention. [Figure 3] FIG. 10 is a schematic diagram of a storage facility according to a third embodiment of the present invention. [Figure 4] FIG. 2 shows the variation of enthalpy (kJ / kg) as a function of pressure (bar) of a portion of the liquid hydrogen fraction extracted from a tank of a storage facility according to the invention. [Figure 5] FIG. 2 shows the variation of the Joule-Thomson coefficient (K / bar) as a function of temperature (K) for different pressures of a portion of the liquid hydrogen fraction extracted from a tank of a storage facility according to the invention. [Figure 6] 1 is a schematic diagram of an example of a compression means for use in a storage facility in accordance with an exemplary embodiment of the present invention; BEST MODE FOR CARRYING OUT THE INVENTION

[0023] In the following description, identical, similar, or analogous elements are designated by the same alphanumeric reference designators.

[0024] The storage facility of the exemplary embodiment of the invention described below comprises a tank 100 for storing a fluid, in particular a two-phase mixture of liquid and gas.

[0025] Tank 100 is a cryogenic tank.

[0026] The fluid is a cryogenic fluid.

[0027] Tank 100 contains fluid at a storage pressure above atmospheric pressure, for example, less than 20 bar, preferably less than 12 bar. Tank 100 is preferably configured to store a volume of fluid of up to 50,000 L at an equilibrium temperature between 3.15 K and 213.15 K, preferably between 18.15 K and 73.15 K.

[0028] Suitable fluids for storage in tank 100 are those that can undergo an enthalpy drop during isothermal compression in the liquid phase. For example, the fluid may be helium or hydrogen. A suitable fluid can be defined by an enthalpy curve at a constant temperature of the liquid fluid that has a substantially parabolic shape with an inflection point. The inflection point is reached when the Joule-Thomson coefficient characteristic of the liquid phase of the fluid is equal to zero. Note that the inflection point of the enthalpy curve changes with temperature.

[0029] Advantageously, the fluid is hydrogen. It should be noted that the temperature of liquid hydrogen is below 33.15 K at atmospheric pressure.

[0030] For the purposes of this invention, hydrogen means parahydrogen, orthohydrogen or a mixture of the two.

[0031] The tank 100 is preferably double-shelled, with a first inner shell intended to contain the fluid, and thus has an insulation optimized to minimize heat exchange between the outside of the tank 100 and the fluid.

[0032] The first shell is preferably surrounded by a second shell, and the tank 100 is provided with insulation in the space (particularly the vacuum space) between the two shells.

[0033] The fluid contained in the first shell of the tank 100 forms a liquid fraction 1002 at the lower portion, i.e., the bottom of the tank 100, and a gas fraction 1004 at the upper portion, i.e., the top of the tank 100, separated from the liquid fraction 1002 by an upper surface.

[0034] Typically, the tank 100 may be equipped with a protective element, such as a valve and / or a rupture disk, that allows the fluid to be released to the outside if the pressure in the first shell exceeds a limit. This limit is typically the maximum allowable pressure of the tank 100 (given by the manufacturer). However, the object of the present invention is to prevent this protective element from being activated, since it is only present in the case of an extreme emergency, in particular if the method according to the present invention malfunctions.

[0035] Preferably, the tank 100 further comprises one or more means for measuring a parameter representative of the fluid pressure inside the first shell of the tank 100. For example, a pressure gauge, an electronic pressure sensor, or any other means for measuring a parameter representative of the pressure of a fluid known to a person skilled in the art can be used as the measuring means.

[0036] The tank 100 is further adapted to supply liquid to one or more demand elements (demand elements not shown), preferably from a portion of the liquid fraction 1002 extracted from the bottom of the tank 100.

[0037] Thus, the tank 100 may further comprise a supply line configured to supply at least a portion of the liquid fraction 1002 contained within the tank 100 to at least one downstream demand element.

[0038] The supply line may include a vaporizer or heater and at least one valve for supplying vaporized gas downstream rather than directly to at least a portion of the extracted liquid fraction 1002. The heater may be a heat exchanger used to convert at least a portion of the liquid fraction 1002 removed from the tank 100 into a gas by exchange with the ambient atmosphere.

[0039] The tank 100 is also typically adapted to be supplied with fluid from one or more external supply elements (external supply elements not shown).

[0040] Therefore, the tank 100 may further comprise a supply circuit for the first shell (supply circuit not shown in the figures).

[0041] For example, the supply circuit comprises a first supply line having an upstream end intended to be connected to a first fluid source (e.g., a hose from a container transported by a truck) and a downstream end connected to the lower part of the first shell of the tank 100.

[0042] The supply circuit may comprise a second supply line having an upstream end intended to be connected to a second fluid source and a downstream end connected to the top of the first shell of the tank 100.

[0043] The upstream ends of the first and second supply lines may be configured to be simultaneously connected to the same fluid source, for example at a common inlet or flange, in which case the first and second fluid sources are combined.

[0044] The upstream ends of the first and second supply lines may also each be configured for simultaneous connection to different fluid sources, where the first and second fluid sources are separate.

[0045] The supply circuit may comprise a set of distribution valves configured to allow fluid from the fluid source to be distributed to either the first or second supply line.

[0046] It should be noted that when feeding the tank 100, the input of heat into the tank 100 causes partial evaporation of the liquid fraction 1002 of the fluid, resulting in an increase in the volume of the gas fraction 1004.

[0047] The storage facility further comprises means 1006 for extracting a portion of the liquid fraction 1002, at least partially connected to the tank 100, in order to obtain a portion of the liquid fraction. The extraction means 1006 is able and configured to ensure that the extraction of a portion of the liquid fraction 1002 is always effective, regardless of the level of the liquid fraction 1002 in the tank 100. For this purpose, the extraction means 1006 comprises an extraction line Cext having an upstream end connected to the first shell, in particular its lower part, and configured to allow extraction of a portion of the liquid fraction 1002 contained in the first shell outside the tank 100, in particular to another element of the storage facility, as soon as the internal pressure of the tank reaches a predetermined value. For example, for this purpose, the extraction means 1006 may further comprise a pilot valve that allows activation or deactivation of the extraction based on the internal pressure of the tank 100.

[0048] Preferably, the storage facility also comprises elements for measuring the temperature and pressure of the extracted portion of the liquid fraction. For example, these measuring elements may be sensors known from the prior art.

[0049] The storage facility further comprises a compression means 120 .

[0050] In the exemplary embodiment shown in FIG. 6, the compression means 120 is a compression device 200 including a compressor element 210 configured to perform the compression and a cooling element 220 for the compressor element 210, which has the effect of cooling the compressor element 210 during the implementation of the compression, i.e., maintaining the temperature of the compressor element 210 by avoiding its overheating. This allows the compression device 200 to perform a substantially isothermal compression of the portion of the liquid fraction 1002 extracted from the tank 100 by the extraction means 1006, in particular by the extraction line Cext. In other words, the temperature of the portion of the liquid fraction entering the compression device 200 is approximately equal to the temperature of the compressed portion leaving the compression device 200.

[0051] Compression device 200 is preferably configured to compress a portion of the extracted liquid fraction to a pressure of 6 to 100 bar at a temperature of 18.15 K to 43.15 K. If the fluid is hydrogen, this pressure is preferably 6 to 70 bar, or even 6 to 40 bar, and the temperature is preferably 28.15 K to 33.15 K.

[0052] The advantage of this type of compressor 200 is that it combines compression and refrigeration functions into a single unit.

[0053] Compressor element 210 of compression device 200 is preferably a piston-type pump, but may also be a gear, lobe, centrifugal pump, or any other suitable pump configured to operate while immersed in a cryogenic liquid.

[0054] The cooling element 220 is preferably a device configured to cool the compressor element 210, in particular a piston-type pump, during the compression thereof. Preferably, as shown in FIG. 6, the cooling element 220 is a storage device defining an internal volume including a lower portion 221 and an upper portion 222. This internal volume contains the volume of a portion of the removed liquid fraction 1002, in particular the portion drawn by the pump but not yet passing through it and therefore not yet compressed. The volume of the portion of the removed liquid fraction 1002 contained in the storage device is preferably large enough to cover the entire lower portion 221, where the pump is located. In this way, the cold portion of the pump is immersed within the volume of the portion of the removed liquid fraction 1002, while its hot portion, including in particular the drive shaft 211, is located outside this volume.

[0055] The storage device further comprises a line 223 for supplying the extracted liquid fraction 1002 to the internal volume. The supply line 223 may be the extraction line Cext or a separate line connected to the extraction line Cext. The supply line 223 is then connected to the extraction means 1006 and opens into the lower section 221 of the internal volume, where the pump inlet E is preferably located. The pump inlet E is arranged in contact with the bottom of the storage device, i.e., the place where the pressure is highest. The storage device also comprises an extraction line 212 connected to the pump outlet S, through which the compressed portion is extracted. For example, the extraction line 212 extends from the lower section 221 to the upper section 222 and opens outside the internal volume.

[0056] The storage device also includes a degassing line 224 that opens into the top 222 of the interior volume.

[0057] In this exemplary embodiment, the liquid fraction 1002 removed prior to passing through the pump is used as a coolant, providing heat exchange through direct contact with the pump to maintain the liquid fraction at temperature during compression. By providing a means for heat exchange to occur directly at the pump rather than in the actual compression section, a compact and easy to use compression means is obtained.

[0058] The advantage of such an arrangement is to have a compact compression means 120 in which the refrigerant corresponds to the refrigerant initially present in the tank 100 and extracted via the extraction means 1006. This brings about obvious savings, since there is no need to extract refrigerant from outside.

[0059] In another exemplary embodiment, the cooling element is a refrigeration unit configured to provide heat exchange with the compression element, through which a different refrigerant than that used in the previous example flows, suitable for cooling the compressor element during compression.

[0060] In another exemplary embodiment, the cooling element is a jacket (or sleeve) placed around the compressor element, inside which a portion of the extracted liquid fraction 1002 flows. Thus, the portion of the portion of the liquid fraction 1002 coming directly from the tank 100 and flowing through the jacket is defined by a lower temperature than the temperature of the liquid fraction being compressed, for example, 20% to 30% of the extracted liquid fraction flowing through the jacket. Preferably, after the portion of the extracted liquid fraction has flowed through the jacket, it is reintroduced into the bottom of the tank 100. Also, there is an obvious cost savings, since there is no need to introduce a coolant from outside.

[0061] In a first exemplary embodiment (the exemplary embodiment shown in FIG. 1), the compression means 120 is connected downstream by a line C11 to an injection means 1008 in the storage facility. The injection means 1008 is able to inject the compressed portion leaving the compression means 120 into the tank 100.

[0062] In this first exemplary embodiment, the compression means 120, optionally associated with an external element, is suitable and configured to perform a substantially isothermal compression and to provide, in the case of hydrogen, a compression portion defined by a predetermined pressure, for example between 6 and 100 bar, preferably between 6 and 70 bar, in the case of hydrogen, and a temperature, in the case of hydrogen, between 18.15 K and 43.15 K, preferably between 28.15 K and 33.15 K. For this first exemplary embodiment, for example a piston, gear pump or lobe pump is suitable as compression means 120.

[0063] The use of such compression means 120 has the advantage of avoiding the expansion of the compressed fraction before it is injected into the tank 100. Indeed, in this first exemplary embodiment, the tank 100 acts as the expansion means, which is then configured to expand the compressed fraction injected into the tank 100 by the injection means 1008. This is possible in this case because the pressure difference between the compressed fraction coming from the compression means 120 and the internal pressure of the tank 100 does not exceed 70 bar. This is possible in this case because the temperature of the compressed fraction coming from the compression means 120 and the internal temperature of the tank 100 are substantially equal.

[0064] In a second exemplary embodiment (the exemplary embodiment shown in FIG. 2), the compression means 120 are connected to the expansion means 160 by a line C12, which is itself connected to the injection means 1008 by another line C22. In other words, the expansion means 160 is connected upstream to the compression means 120 and downstream to the injection means 1008. The combination of the compression means 120 and the expansion means 160 makes it possible in particular to control or adjust the pressure of the compressed portion obtained at the outlet of the compression means 120. The compression means 120, optionally associated with an external element, is suitable and configured to perform a substantially isothermal compression and to provide a compressed portion defined by a predetermined pressure, for example between 6 and 100 bar, preferably between 6 and 70 bar if the fluid is hydrogen, and a temperature between 18.15 K and 43.15 K, preferably between 28.15 K and 33.15 K if the fluid is hydrogen. The expansion means 160 is suitable and configured to perform a preferably isenthalpic expansion of the compressed portion, providing an expanded portion defined by a predetermined pressure, e.g., less than 20 bar, preferably less than 12 bar, when the fluid is hydrogen. Furthermore, the expansion means 160 is preferably configured to perform the isenthalpic expansion at a temperature between 3.15 K and 213.15 K, preferably between 18.15 K and 73.15 K, when the fluid is hydrogen. To this end, the expansion means 160 includes a valve. For example, the valve may be a disc valve or a porous orifice valve.

[0065] Advantageously, the expansion means 160 comprises a throttle valve 162, which makes it possible to precisely regulate the pressure of the compressed portion and to adjust the pressure of the compressed and expanded portion, and which may for example be a Joule-Thomson valve.

[0066] In this second exemplary embodiment, the pressure difference between the compressed portion coming from the compression means 120 and the expanded portion coming from the expansion means 160 is preferably between 6 and 70 bar. Furthermore, the temperature of the compressed portion coming from the compression means 120 is higher than the temperature of the expanded portion.

[0067] In this second exemplary embodiment, the injection means 1008 is configured to then inject the previously compressed expanded portion into the tank 100 .

[0068] In the third exemplary embodiment (the exemplary embodiment shown in [Figure 3]), the storage facility comprises, in particular, the compression means 120, the expansion means 160 and the injection means 1008 of the second exemplary embodiment, and further comprises a buffer tank 140 to which the compression means 120 is connected upstream by a first transfer line C13.

[0069] The buffer tank 140 is connected downstream to the expansion means 160 by a second transfer line C23. The buffer tank 140 is therefore particularly arranged between the compression means 120 and the expansion means 160.

[0070] This buffer tank 140 stores several volumes of compressed portions before carrying out their total expansion in the expansion means 160. For this purpose, the buffer tank 140 is configured to allow the volume contained therein to be transferred to the expansion means 160 when its internal pressure reaches a predetermined value, for example 6 to 70 bar.

[0071] The injection means 1008 is connected to the expansion means 160 by a third transfer line C33. The injection means 1008 can inject the compressed and expanded portion coming out of the expansion means 160 into the tank 100.

[0072] It should be noted that one or more of the lines included in this storage facility may be equipped with at least one specific valve and / or one regulating means capable of controlling the flow rate of the fluid flowing therethrough.

[0073] Furthermore, one or more of the lines included in this storage facility are advantageously equipped with an insulating jacket (insulating jacket not shown).

[0074] As mentioned above, it should be noted that the storage facility is a closed cycle.

[0075] A method for controlling the internal pressure of the tank 100 included in the storage facility disclosed above will now be disclosed below with reference to the different states in which the portion of the liquid fraction removed during the course of the method finds itself, in particular after each thermodynamic transformation (compression, expansion).

[0076] Tank 100 contains a fluid, preferably liquid hydrogen, forming a liquid fraction 1002 and a gas fraction 1004. Thus, in a preliminary step, a step of feeding tank 100 is carried out via a supply circuit. This feeding step is preferably carried out by transferring liquid hydrogen from a first liquid hydrogen source to a first shell of tank 100 using a first supply line of the supply circuit.

[0077] It should be noted that the step of supplying the required component can be carried out at any time during the method, in particular via a supply line, simultaneously with or separately from the implementation of one or more steps of the method according to the invention. This supply step can be carried out several times during the method according to the invention.

[0078] After the feeding step, thermodynamic equilibrium is established in the tank 100, with identical pressures between the gas fraction 1004 and the liquid fraction 1002. Heat exchange generally takes place in the tank 100, resulting in heating of the liquid fraction 1002. As a result, the thermodynamic equilibrium changes. The part of the liquid fraction 1002 corresponding to the heat loss then evaporates. When the facility is in a closed cycle, the gas fraction 1004 and the pressure in the tank 100 increase. However, if the increase in the gas fraction 1004 and the pressure is too great, it becomes difficult or even impossible to feed the tank 100.

[0079] Therefore, according to the present invention, to compensate for these increases in gas fraction 1004 and pressure, a portion of the liquid fraction 1002 of the fluid is removed from the tank 100 via the extraction line Cext during the removal step.

[0080] The withdrawal step is preferably carried out after carrying out a step of measuring a parameter representative of the pressure of the gas fraction 1004 and / or a parameter representative of the pressure of the liquid fraction 1002. Depending on one and / or the other of these two parameters, the withdrawal step and subsequent steps are carried out.

[0081] After the extraction step, the extracted portion defined in state A is thus obtained as follows: a first temperature T1, - first pressure P1, - the first enthalpy E1, and -First density D1.

[0082] The removed portion of state A is composed of only liquid phase, with no gas phase present. In particular, this removed portion lies on the characteristic liquid saturation curve of the fluid.

[0083] In one variation, point A may be far away from or substantially close to the characteristic liquid saturation curve of the fluid while still in the liquid portion.

[0084] Using this removal and subsequent steps, the pressure of the gas fraction 1004 at the top of the tank 100 is adjusted so that this pressure is maintained below a predetermined value, for example, below 20 bar, preferably below 12 bar if the fluid is hydrogen.

[0085] Preferably, the removal step is performed discontinuously, for example, whenever the pressure in the tank 100 reaches or exceeds a predetermined value.

[0086] Preferably, during this extraction step, the flow rate and volume of the liquid portion of the extracted fluid is determined by the characteristics of the compression means 120, i.e. by the nominal flow rate.

[0087] Then, in a subsequent step, this removed portion is compressed in compression means 120. This compression is substantially isothermal, resulting in a compressed portion at state B defined by the following equation: a second temperature T2 substantially equal to the first temperature T1; a second pressure P2 greater than the first pressure P1, and a second density D2 greater than the first density D1;

[0088] Advantageously, the compression step is carried out over a pressure range of 6 to 100 bar, preferably 6 to 70 bar, when the fluid is hydrogen. It should be noted that the pressure increase associated with this compression is specific to the properties of the compressed fluid.

[0089] Note that compression can result in a decrease in enthalpy between a first enthalpy E1 at state A and a second enthalpy E2 at state B over a given pressure range. Compression between states A and B is essentially isentropic. This decrease in enthalpy is possible because the Joule-Thomson coefficient (K / bar) is positive for the given pressure range, while the compression is substantially isothermal. Note that the positive Joule-Thomson coefficient of the liquid saturated phase is indicated by the fact that the slope of the curve showing the change in enthalpy (kJ / kg) with pressure (bar) is negative for this given pressure range. This compression is irreversible.

[0090] Advantageously, the compression step results in a continuous decrease in the enthalpy of the removed portion from state A to state B.

[0091] Preferably, the compression process is carried out from state A to state B as long as the characteristic Joule-Thomson coefficient of the fluid is positive. This maximizes the efficiency of the facility.

[0092] However, the compression process is advantageously stopped when the enthalpy drop in the compression section is less than 0.1 kJ / kg per 1 bar pressure increase. It should be noted that if the compression process is continued with an enthalpy drop of less than 0.1 kJ / kg, it will be difficult to take advantage of the inflection point of the enthalpy curve at a constant temperature without using a large amount of energy.

[0093] If the tank 100 is also the expansion means 160 (see FIG. 1), the compressed portion then flows through a transfer line C11 connecting the compression means 120 to the injection means 1008.

[0094] When the compression means 120 is directly or indirectly connected to the expansion means 160 upstream of the injection means 1008 (see Figures 2 and 3), the compressed portion flows through a transfer line C12 connecting the compression means 120 to the expansion means 160 or through a transfer line C13 connecting the compression means 120 to the buffer tank 140.

[0095] When the compression means 120 is connected to the buffer tank 140, when the internal pressure of the buffer tank 140 reaches a predetermined pressure, preferably 6 to 70 bar, the compressed portion stored in the buffer tank 140 flows through the second transfer line C23 leading to the expansion means 160.

[0096] In a next step, the compressed portion is then subjected to expansion to obtain an expanded portion defined in state C by the following formula: a third temperature T3 lower than the second temperature T2; a third pressure P3 lower than the second pressure P2, and a third density D3 that is smaller than the second density D2 and greater than the first density D1;

[0097] According to the implementation of the exemplary embodiment shown in FIG. 1, the expansion is performed during or after the step of injecting the compressed portion into the tank 100, if the tank 100 is also the expansion means. In this case, state C is defined as the equilibrium state in the tank 100 after the injection of the compressed portion. Thus, here, the expansion can be initiated and performed in the tank 100 during the injection.

[0098] In this first exemplary embodiment shown in FIG. 1, the expansion is not isenthalpic: the portion injected into the tank 100 is also defined by a third enthalpy E3, which is smaller than the first enthalpy E1 of the portion withdrawn. This means that the internal temperature of the tank 100 decreases after thermodynamic equilibrium.

[0099] 2 and 3, if the facility comprises an expansion means 160 separate from the tank 100, the expansion takes place between the compression step and the subsequent step of injecting the expanded portion into the tank 100. In this case, state C is defined as the state in which the expanded portion finds itself before being injected into the tank 100. As a result, the portion leaving the expansion means 160 has properties close to the thermodynamic conditions of the tank 100.

[0100] According to the implementation of the exemplary embodiment shown in Figures 2 and 3, the expansion is preferably isenthalpic. Such an isenthalpic expansion has the advantage that it does not generate heat.

[0101] Preferably, at state C, the expansion portion is substantially on the characteristic liquid saturation curve of the fluid. For example, at state C, P3 may be between P1 and P2, preferably between P1 and the liquid saturation pressure of the fluid plus 0.1 bar. This also facilitates the injection of the injection into tank 100.

[0102] The portion injected into the tank 100 is also defined by a third enthalpy E3, which is smaller than the first enthalpy E1 of the portion removed. This means a decrease in the internal temperature of the tank 100 after thermodynamic equilibrium. The portion injected into the tank 100 is therefore defined, inter alia, by a third temperature T3, which is lower than the first temperature T1, so as to compensate for the heating in the tank 100. This avoids a pressure increase in the tank 100, which would be unavoidable if the method according to the invention were not implemented. [Example]

[0103] The storage facility according to the second exemplary embodiment was implemented using hydrogen as the fluid.

[0104] The following table of experimental results can be read in conjunction with the diagrams shown in Figures 4 and 5, with reference to conditions A, B, and C described above.

[0105] As shown in Figure 4, the enthalpy curve at a constant liquid hydrogen temperature approximately equal to 30 K has a substantially parabolic shape. At state B, there is an inflection point on the enthalpy curve, which corresponds to the enthalpy minimum over the pressure range from 8 bar to 30 bar.

[0106] As shown in Figure 5, for hydrogen, isenthalpic expansion can only be implemented above a pressure of 5 bar, where the Joule-Thomson coefficient becomes positive.

[0107] In particular, the following table of experimental results gives a clearer idea of ​​the advantages of implementing the method according to the invention.

[0108] This table contains the temperature (in K), pressure (in bar), density (in kg / m) of the hydrogen initially contained in the tank 100 and then found in the above-mentioned states A, B and C, and flowing through the above-mentioned facility according to the above-mentioned method of the invention, as shown in FIG. 3 unit), volume (m 3 / kg), specific internal energy (kJ / kg), and enthalpy (kJ / kg) values ​​are shown.

[0109] [Table 1]

[0110] From this table, the following conclusions can be drawn: A substantially isenthalpic expansion effectively occurs between states B and C. Furthermore, in state C, the temperature T3 is much lower than the temperature T1 defined in state A. Thus, the density D3 defined in state C is much higher than the density D1 defined in state A.

[0111] Of course, the present invention is not limited to the particular examples disclosed and shown in this application: other variations or embodiments within the reach of a person skilled in the art can be envisioned without departing from the scope of the invention as defined by the claims.

Claims

1. 1. A method for controlling the internal pressure of a cryogenic tank (100) containing a liquid fraction (1002) and a gas fraction (1004) of a fluid, the enthalpy of which can be reduced during isothermal compression in the liquid phase, the method comprising: - removing a portion of said liquid fraction and subjecting it to the treatment in condition A; a first temperature T1, a first pressure P1, the first enthalpy E1, and obtaining an extracted portion defined by a first density D1; - compressing the removed portion substantially isothermally to form a a second temperature T2 substantially equal to said first temperature T1, a second pressure P2 greater than said first pressure P1, and obtaining a compressed part defined by a second density D2 greater than said first density D1, said compression being intended to result in a decrease in enthalpy between said first enthalpy E1 at state A and said second enthalpy E2 at state B; - expanding the compressed portion to state C, a third temperature T3 lower than said second temperature T2, a third pressure P3 lower than said second pressure P2, and - obtaining an expanded portion defined by a third density D3 less than said second density D2 and greater than said first density D1; - injecting said compressed or expanded portion into said tank (100), The expansion is carried out after the injection step when the compressed portion is injected into the tank (100), or The method, wherein the expansion is performed between the compressing step and the injecting step when the expanded portion is injected into the tank (100).

2. 2. The method of claim 1, wherein the compressing step results in a continuous decrease in the enthalpy of the removed portion from state A to state B.

3. 3. The method of claim 2, wherein the compression step is stopped when the decrease in enthalpy of the compressed portion is less than 0.1 kJ / kg at a pressure increase of 1 bar.

4. The method of claim 1 wherein the fluid is hydrogen.

5. The method according to any one of claims 1 to 4, wherein the third pressure P3 is greater than or substantially equal to the first pressure P1.

6. 6. The method of any one of claims 1 to 5, wherein the expansion is a substantially isenthalpic expansion when carried out between the compressing step and the injecting step.

7. A facility for storing a liquid fraction (1002) and a gas fraction (1004) of a fluid, configured to implement the method according to any one of claims 1 to 6, said facility comprising: a cryogenic tank (100) intended to contain said fluid; - means (1006) for removing a portion of said liquid fraction (1002); compression means (120) comprising a compressor element (210) and a cooling element (220) for said compressor element (210) configured to maintain said compressor element (210) at a temperature during compression to achieve a substantially isothermal compression of said withdrawn portion to obtain a compressed portion; - expansion means (160) capable of expanding said compressed portion to obtain an expanded portion; and - injection means (1008) capable of injecting said compressed or expanded portion into said cryogenic tank (100); The facility, wherein the expansion means (160) and the tank (100) are combined or separate.

8. 8. The facility of claim 7, further comprising a buffer tank (140) disposed between the compression means (120) and the expansion means (160).

9. 9. The installation according to claim 7 or 8, wherein the expansion means (160) comprises a throttle valve (162).

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