Method for controlling the internal pressure of a cryogenic tank

Abstract

The invention relates to a method for controlling the internal pressure of a cryogenic tank (100) containing a liquid fraction (1002) and a gaseous fraction (1004) of a fluid whose enthalpy can decrease during isothermal compression in the liquid phase. Figure for the abstract: Figure 3

Description

Title of the invention: Method for controlling the internal pressure of a cryogenic tank Technical field of the invention

[0001] The invention belongs to the technical field of cryogenic tanks. The invention relates more specifically to a method for controlling the internal pressure of a cryogenic tank. The invention further relates to an installation for storing a cryogenic fluid.

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

[0003] Cryogenic fluid means any fluid that has been cooled to a temperature below its boiling point. Technical background

[0004] The invention applies particularly to cryogenic tanks capable of storing a cryogenic fluid at a pressure of less than 20 bar. The pressure indicated here and the pressures indicated subsequently are in absolute bars.

[0005] Such tanks are commonly used to store cryogenic fluid, which, at atmospheric pressure, is liquid at a temperature below 273.15 K, in particular below 213.15 K. Conventionally, these tanks belong to a storage installation.

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

[0007] For example, as requesting elements, mention may be made of elements capable of receiving fluid from a reservoir. For example, these elements may be vehicles configured to receive and store fluid.

[0008] For example, as external supply elements, mention may be made of elements capable of supplying a reservoir with a quantity of fluid in liquid or gaseous form.

[0009] In such storage facilities, the cryogenic fluid is initially stored in the liquid state but inevitably develops evaporation gases so as to form, in the tank, both a liquid fraction at the bottom of the tank and a gaseous fraction at the top of the tank. A portion of this gaseous fraction resulting from the evaporation gases is usually discharged to the atmosphere without being used. Conventionally, this discharge is made possible by a protective member that includes the tank such as a valve and / or a rupture disc allowing a release of at least part of the gaseous fraction to the outside in the event of pressure exceeding a limit in the tank. This limit is typically the maximum admissible pressure of the tank, a limit usually given by the manufacturer.

[0010] However, the evaporation gases released into the atmosphere constitute both an ecological and economic disadvantage.

[0011] This is why various systems and methods for managing the internal pressure of a tank have been considered to prevent the evacuation of these evaporation gases to the outside. These systems and methods consist either in consuming a portion of the liquid fraction contained in the tank so as to regularly lower the internal pressure of the tank, or in extracting a portion of the gaseous fraction from the tank and recompressing it via a complex and expensive gas compression system.

[0012] However, for obvious ecological and economic reasons, such solutions cannot be considered for commercial applications to storage facilities.

[0013] An aim of the present invention is therefore to overcome all or part of the drawbacks noted above. Summary of the invention

[0014] To this end, the invention proposes a simple method, which is inexpensive to implement, which makes it possible to control the internal pressure of a cryogenic tank so as to prevent at least part of the gaseous fraction from being evacuated from the cryogenic tank due to an excessive rise in its internal pressure.

[0015] To this end, there is proposed firstly a method for controlling the internal pressure of a cryogenic tank containing a liquid fraction and a gaseous fraction of a fluid whose enthalpy can decrease during isothermal compression in the liquid phase, the method comprising the following steps: - taking a portion of the liquid fraction to obtain a taken portion defined at state A by: - a first temperature Tl, - a first PI pressure, - a first enthalpy El, and - a first density Dl, - substantially isothermal compression of the portion taken to obtain a compressed portion defined at state B by: - a second temperature T2 substantially equal to the first temperature T1, - a second pressure P2 greater than the first pressure PI, and - a second density D2 greater than the first density Dl, said compression being capable of leading to a reduction in enthalpies between the first enthalpy El of state A and a second enthalpy E2 of state B, - expansion of the compressed portion to obtain a relaxed portion defined at a state C by: - 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 lower than the second density D2 and higher than the first density D1, - injection of the compressed portion or the expanded portion into the storage tank, said relaxation being carried out during or after the injection step when the compressed portion is injected into the reservoir, or said expansion being carried out between the compression step and the injection step when the expanded portion is injected into the reservoir.

[0016] The method according to the invention makes it possible to oppose an increase in the internal pressure of the cryogenic tank caused naturally by its ambient environment. Thus, an evacuation from the tank of a part of the gaseous fraction, for example by the actuation of a safety valve or through the walls of the cryogenic tank, is avoided.

[0017] Various additional features may be provided alone or in combination: - the compression step leads to a continuous decrease in the enthalpy of the portion taken from state A to state B, - the compression stage is stopped when the enthalpy drop of the compressed portion 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 PI, - the expansion is a substantially isenthalpic expansion when it is carried out between the compression stage and the injection stage.

[0018] Secondly, there is proposed an installation for storing a liquid fraction and a gaseous fraction of a fluid capable of implementing the method described above, the installation comprising: - a cryogenic tank intended to contain the fluid, - a means of collecting a portion of the liquid fraction, - a compressor means capable of carrying out a substantially isothermal compression of the portion taken to obtain a compressed portion, - a relaxation means capable of relaxing the compressed portion to obtain a relaxed portion, and - an injector means capable of injecting the compressed portion or the expanded portion into the cryogenic tank, installation in which the pressure reducing means and the tank are either the same or separate.

[0019] The installation according to the invention has the advantage of being compact and easy to implement. In addition, this installation is composed only of simple and economical elements.

[0020] Various additional features may be provided alone or in combination: - the installation further comprises a buffer tank arranged between the compressor means and the expansion means, - the pressure reducing means comprises a throttle valve.

[0021] The invention may also relate to any alternative method or device comprising any combination of the above or below features. Brief description of the figures

[0022] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0023] [Fig.l] [Fig.l] is a schematic representation of a storage installation according to a first exemplary embodiment of the invention.

[0024] [Fig.2] [Fig.2] is a schematic representation of a storage installation according to a second exemplary embodiment of the invention.

[0025] [Fig.3] [Fig.3] is a schematic representation of a storage installation according to a third exemplary embodiment of the invention.

[0026] [Fig.4] [Fig.4] is a diagram showing the evolution of the enthalpy (in kJ / kg) as a function of the pressure (in bar) of a part of a liquid fraction of hydrogen extracted from a tank of a storage installation according to the invention.

[0027] [Fig.5] [Fig.5] is a diagram showing the evolution of the Joule-Thomson coefficient (in K / bar) as a function of the temperature (in K) for different pressures of a part of a liquid fraction of hydrogen extracted from a tank of a storage installation according to the invention. Detailed description of the invention

[0028] In the following description, identical, similar or analogous elements will be designated by the same alphanumeric references.

[0029] The storage facility of the exemplary embodiments of the invention described below comprises a reservoir 100 for storing fluid and in particular a two-phase mixture of liquid and gas.

[0030] The tank 100 is a cryogenic tank.

[0031] The fluid is a cryogenic fluid.

[0032] The reservoir 100 contains the fluid under a storage pressure greater than atmospheric pressure, for example under a pressure less than 20 bar, preferably less than 12 bar. The reservoir 100 is preferably configured to store a volume of fluid of up to 50,000 L at an equilibrium temperature of between 3.15K and 213.15 K, preferably between 18.15 K and 73.15 K.

[0033] The fluid suitable for storage in the tank 100 is a fluid whose enthalpy can decrease during isothermal compression in the liquid phase. For example, the fluid can be helium or hydrogen. The suitable fluid can be defined by a constant temperature enthalpy curve of the liquid fluid which has a substantially parabolic shape with an inflection point. The inflection point is reached when the characteristic Joule-Thomson coefficient of the liquid phase of the fluid is equal to zero. It should be noted that the inflection point of the enthalpy curve varies with temperature.

[0034] Advantageously, the fluid is hydrogen. It should be noted that the temperature of liquid hydrogen is less than 33.15 K at atmospheric pressure.

[0035] For the purposes of the present invention, hydrogen means para hydrogen, ortho hydrogen or a mixture of the two.

[0036] The tank 100 is preferably double-jacketed, comprising a first internal jacket intended to contain the fluid. In this way, the tank 100 has optimized thermal insulation to minimize thermal exchanges between the exterior of the tank 100 and the fluid.

[0037] The first envelope is preferably surrounded by a second envelope and the reservoir 100 comprises thermal insulation in the space between the two envelopes (in particular a vacuum space).

[0038] The fluid contained in the first envelope of the reservoir 100 forms a liquid fraction 1002 in the lower part, that is to say at the bottom of the reservoir 100, and a gaseous fraction 1004 in the upper part, that is to say at the top of the reservoir 100, separated by an upper surface of the liquid fraction 1002.

[0039] Conventionally, the reservoir 100 may comprise a protective member such as a valve and / or a rupture disk allowing fluid to be released to the outside in the event of pressure exceeding a limit in the first casing. This limit is typically the maximum admissible pressure of the reservoir 100 (given by the manufacturer). However, the invention aims to avoid the actuation of this protective member, the latter being present only in the event of extreme emergency, in par- particular if the method according to the invention malfunctions.

[0040] Preferably, the reservoir 100 further comprises one or more means for measuring a parameter representative of the pressure of the fluid inside the first casing of the reservoir 100. For example, as measuring means, mention may be made of a pressure gauge, an electronic pressure sensor or any other means for measuring a parameter representative of the pressure of a fluid known to those skilled in the art.

[0041] This reservoir 100 is further adapted to supply one or more demand elements with liquid preferably from a part of the liquid fraction 1002 extracted from the bottom of the reservoir 100 (demand elements not shown in the figures).

[0042] The reservoir 100 may therefore further comprise a supply pipe arranged to supply downstream to at least one requesting element at least part of the liquid fraction 1002 contained in the reservoir 100.

[0043] The supply line may comprise a vaporizer, or heater, and at least one valve for supplying vaporized gas downstream rather than directly at least part of the liquid fraction 1002 extracted. This heater may be a heat exchanger used to transform at least part of the liquid fraction 1002 drawn from the reservoir 100 into gas by exchange with the ambient atmosphere.

[0044] This reservoir 100 is also conventionally adapted to be supplied with fluid from one or more external supply elements (external supply elements not shown in the figures).

[0045] The reservoir 100 can therefore further comprise a supply circuit for the first envelope (supply circuit not shown in the figures).

[0046] For example, this supply circuit comprises a first supply pipe having an upstream end intended to be connected to a first source of fluid (such as a hose of a container transported by a truck for example) and a downstream end connected to the lower part of the first casing of the tank 100.

[0047] The supply circuit may comprise a second supply pipe having an upstream end intended to be connected to a second source of fluid and a downstream end connected to the upper part of the first casing of the reservoir 100.

[0048] The upstream ends of the first and second supply lines may be configured to be connected simultaneously to the same fluid source, for example at a common inlet or flange. In this case, the first and second fluid sources are the same.

[0049] The upstream ends of the first and second supply lines may also each be configured to be simultaneously connected to different fluid sources. In this case, the first and second fluid sources are distinct.

[0050] The supply circuit may include a set of distribution valve(s) configured to allow distribution of fluid from the fluid source(s) into either the first or second supply lines.

[0051] It should be noted that, when supplying the reservoir 100, any heat input into the reservoir 100 will cause partial vaporization of the liquid fraction 1002 of the fluid, which has the consequence of increasing the volume of the gaseous fraction 1004.

[0052] The storage installation further comprises a means 1006 for withdrawing a portion of the liquid fraction 1002 which is at least partly connected to the reservoir 100 in order to obtain a portion of the liquid fraction. The withdrawal means 1006 is suitable 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 reservoir 100. To this end, the withdrawal means 1006 comprises an extraction pipe Cext having an upstream end connected to the first casing, in particular to its lower part, and configured to allow the extraction of a portion of the liquid fraction 1002 contained in the first casing to the outside of the reservoir 100, in particular to other elements of the storage installation, as soon as the internal pressure of the reservoir reaches a predetermined value.For example, the sampling means 1006 may for this purpose also comprise a controlled valve to enable extraction to be activated or not depending on the internal pressure of the reservoir 100.

[0053] Preferably, the storage facility also comprises elements for measuring the temperature and pressure of the portion of the liquid fraction extracted. For example, these measuring elements may be sensors known from the prior art.

[0054] The storage facility further comprises a compressor means 120.

[0055] According to one embodiment, the compressor means is capable of carrying out a substantially isothermal compression of the portion of the liquid fraction 1002 extracted from the reservoir 100 by the sampling means 1006, in particular extracted by the extraction pipe Cext.

[0056] According to another embodiment, the compressor means 120 may be associated with an external element, this association allowing the compressor means 120 to carry out a substantially isothermal compression of the portion of the liquid fraction 1002 extracted from the reservoir 100 by the sampling means 1006, in particular extracted by the extraction pipe Cext. For example, as an external element, a refrigeration unit may be cited.

[0057] The compressor means 120, possibly associated with the external element, makes it possible to obtain a compressed portion downstream. The compressor means 120, possibly associated with the external element, is preferably configured to compress the portion of the extracted liquid fraction to a pressure of between 6 and 100 bar, preferably between 6 and 70 bar when the fluid is hydrogen, and to a temperature of between 18.15 K and 43.15 K, preferably between 28.15 K and 33.15 K when the fluid is hydrogen. For example, the compressor means 120 may be of the piston, gear, lobe, centrifugal type or any other appropriate technology.

[0058] It should be noted that the compressor means 120, possibly associated with the external element, may comprise a casing (or jacket) arranged on its periphery and inside which circulates a part of the portion of the extracted liquid fraction 1002. Thus, the part of the portion of the liquid fraction 1002 coming directly from the reservoir 100 and circulating in the casing is defined by a temperature lower than that of the liquid fraction being compressed. For example, 20% to 30% of the extracted liquid fraction circulates in the casing. Preferably, after the part of the portion of the extracted liquid fraction has circulated in the casing, it is reintroduced into the reservoir 100 at its lower part.

[0059] Furthermore, the storage installation may further comprise an additional device (additional device not shown in the figures) known to those skilled in the art, and arranged upstream of the compressor means 120, possibly associated with the external element, configured to cool the portion of the extracted liquid fraction to be compressed. This additional device may be an integral part of the compressor means 120. For example, this additional device may be a second refrigeration unit.

[0060] In a first exemplary embodiment (exemplary embodiment shown in [Fig.l]), the compressor means 120 is connected downstream by a pipe Cl 1 to an injector means 1008 which the storage installation comprises. The injector means 1008 is capable of injecting the compressed portion leaving the compressor means 120 into the reservoir 100.

[0061] In this first embodiment, the compressor means 120, possibly associated with the external element, is capable and configured to carry out 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, when the fluid is hydrogen and at a temperature between 18.15 K and 43.15 K, preferably between 28.15 K and 33.15 K when the fluid is hydrogen. For example, as compressor means 120 suitable for this first embodiment, mention may be made of pistons, gear pumps or even lobe pumps.

[0062] The use of such a compressor means 120 has the advantage of avoiding expansion of the compressed portion before it is injected into the reservoir 100. Indeed, in this first embodiment, the reservoir 100 behaves as an expansion means. The reservoir is then configured to expand the compressed portion injected into the reservoir 100 by the injector means 1008. This is made possible because in this case, the pressure difference between the compressed portion coming from the compressor means 120 and the internal pressure of the reservoir 100 does not exceed 70 bar. This is also made possible because in this case, the temperature of the compressed portion coming from the compressor means 120 and the internal temperature of the reservoir 100 are substantially equal.

[0063] In a second exemplary embodiment (exemplary embodiment shown in [Fig. 2]), the compressor means 120 is connected to a pressure reducing means 160 by a pipe C12, the pressure reducing means 160 itself being connected to the injector means 1008 by another pipe C22. In other words, the pressure reducing means 160 is connected upstream to the compressor means 120 and connected downstream to the injector means 1008. The combination of the compressor means 120 and the pressure reducing means 160 makes it possible in particular to control, or adjust, the pressure of the compressed portion obtained at the outlet of the compressor means 120.The compressor means 120, possibly associated with the external element, is capable and configured to carry out 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 when the fluid is hydrogen, and at a temperature between 18.15 K and 43.15 K, preferably between 28.15 K and 33.15 K when the fluid is hydrogen. The expansion means is capable and configured to carry out a preferably isenthalpic expansion of the compressed portion and to provide an expanded portion defined by a predetermined pressure, for example less than 20 bar, preferably less than 12 bar when the fluid is hydrogen.Furthermore, the expansion means 160 is configured to carry out a preferably isenthalpic expansion at a temperature between 3.15K 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 comprises a valve. For example, the valve may be a disc or porous orifice valve.

[0064] Advantageously, the pressure reducing means 160 comprises a throttling valve 162. This throttling valve 162 makes it possible to precisely regulate the pressure of the compressed portion, then to adjust the pressure of the compressed then expanded portion.

[0065] In this second embodiment, the pressure difference between the compressed portion from the compressor means 120 and the expanded portion from the expansion means 160 is preferably between 6 and 70 bar. In addition, the temperature of the compressed portion from the compressor means 120 is greater than the expanded portion.

[0066] In this second exemplary embodiment, the injector means 1008 is then configured to inject into the reservoir 100 the expanded portion which has been previously compressed.

[0067] In a third exemplary embodiment (exemplary embodiment illustrated in [Fig. 3]), the storage installation notably comprises the compressor means 120, the expansion means 160 and the injector means 1008 of the second exemplary embodiment and further comprises a buffer tank 140 upstream of which the compressor means 120 is connected by a first transfer pipe Cl3.

[0068] The buffer tank 140 is connected downstream, by a second transfer line C23, to the pressure reducing means 160. The buffer tank 140 is therefore in particular arranged between the compressor means 120 and the pressure reducing means 160.

[0069] This buffer tank 140 makes it possible to store several volumes of compressed portions before carrying out an overall expansion in the expansion means 160 of these several volumes of compressed portions. To this end, the buffer tank 140 is configured to allow the passage of the volume that it contains towards the expansion means 160 once its internal pressure has reached a predetermined value, for example between 6 and 70 bar.

[0070] The injector means 1008 is connected to the pressure reducing means 160 by a third transfer line C33. The injector means 1008 is capable of injecting into the reservoir 100 the compressed then expanded portion leaving the pressure reducing means 160.

[0071] It should be noted that one or more of the pipes included in this storage installation may be provided with at least one specific valve and / or a regulating means capable of controlling the flow rate of fluid circulating inside them.

[0072] Furthermore, one or more of the pipes included in this storage installation advantageously comprise thermal insulation envelopes (thermal insulation envelopes not shown in the figures).

[0073] As indicated above, it should be noted that the storage facility is in a closed cycle.

[0074] A method for controlling the internal pressure of the tank 100 included in the storage installation described above will now be described below with reference to the different states in which the portion of the liquid fraction taken during the course of the process is found, in particular after each thermodynamic transformation (compression, expansion).

[0075] The tank 100 contains the fluid, preferably liquid hydrogen, forming the liquid fraction 1002 and the gaseous fraction 1004. Thus, in a prior step, a step of supplying the tank 100 is carried out via the circuit supply. This supply step is preferably carried out via a transfer of liquid hydrogen, using the first supply line of the supply circuit, from the first source of liquid hydrogen to the first casing of the tank 100.

[0076] It should be noted that a step of supplying requesting elements can be carried out via the supply line at any time during the method, in particular simultaneously or not with 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.

[0077] After the supply step, a thermodynamic equilibrium is established in the tank 100 to have an identical pressure between the gaseous fraction 1004 and the liquid fraction 1002. A heat exchange generally takes place in the tank 100 and results in a heating of the liquid fraction 1002. The thermodynamic equilibrium will change accordingly. A portion of the liquid fraction 1002 equivalent to the heat loss then vaporizes. As the installation is in a closed cycle, the gaseous fraction 1004 and the pressure increase in the tank 100. However, if the increase in the gaseous fraction 1004 and the pressure is too great, it becomes difficult, or even impossible, to supply the tank 100.

[0078] To compensate for these increases in the gas fraction 1004 and in the pressure, according to the invention, a portion of the liquid fraction 1002 of the fluid is therefore taken, during a sampling step, from the reservoir 100 via the extraction pipe Cext.

[0079] The sampling step is preferably implemented 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 sampling step and the following steps are implemented.

[0080] After the sampling step, we thus obtain a sampled portion defined at a state A by: - a first temperature Tl, - a first PI pressure, - a first enthalpy El, and - a first DI density.

[0081] The sampled portion which is in state A does not have a gaseous phase and is only made up of a liquid phase. In particular, this sampled portion is then found on the characteristic liquid saturation curve of the fluid.

[0082] In an alternative embodiment, point A may be far from or substantially close to the characteristic liquid saturation curve of the fluid, while being in the liquid part.

[0083] Using this sampling and the steps that follow, the pressure of the gas fraction 1004 at the top of the reservoir 100 is regulated so that this pressure remains lower than a predetermined value, for example lower than 20 bar, preferably lower than 12 bar when the fluid is hydrogen.

[0084] Preferably, the sampling step is implemented discontinuously. For example, the sampling step may be implemented each time the internal pressure of the tank 100 becomes equal to or greater than the predetermined value.

[0085] Preferably, during this sampling step, the flow rate and the volume of the liquid portion of the extracted fluid are determined by the characteristics of the compressor means 120, i.e. by a nominal flow rate.

[0086] Then, in a subsequent step, this sampled portion is compressed in the compressor means 120. This compression is a substantially isothermal compression following which a compressed portion is obtained defined at a state B by: - a second temperature T2 substantially equal to the first temperature Tl, - a second pressure P2 greater than the first pressure PI, and - a second density D2 greater than the first density Dl.

[0087] Advantageously, the compression step is carried out over a pressure range of between 6 and 100 bar, preferably between 6 and 70 bar when the fluid is hydrogen. It should be noted that the pressure increase associated with this compression is inherent in the characteristics of the compressed fluid.

[0088] It should be noted that the compression is capable of leading to a decrease in enthalpy between the first enthalpy E1 of state A and a second enthalpy E2 of state B over a predefined pressure range. The compression between state A and state B is substantially isentropic. This decrease in enthalpy is permitted because the Joule-Thomson coefficient (in K7 bar) is positive for the predefined pressure range while the compression is substantially isothermal. It should be noted that the positive nature of the Joule-Thomson coefficient for a liquid-saturated phase is illustrated by the fact that, for this predefined pressure range, the slope of the curve showing the change in enthalpy (in kJ / kg) as a function of pressure (in bar) is negative. This compression is irreversible.

[0089] Advantageously, the compression step leads to a continuous decrease in the enthalpy of the portion taken from state A to state B.

[0090] Preferably, the compression step is carried out from state A to state B as long as the characteristic Joule-Thomson coefficient of the fluid is positive. This makes it possible to maximize the efficiency of the installation.

[0091] However, the compression step is advantageously stopped when the drop in enthalpies of the compressed portion is less than 0.1 kJ / kg for an increase of pressure of 1 bar. It should be noted that if the compression step continued while the enthalpy drop was less than 0.1 kJ / kg, it would be difficult to exploit the inflection point of the enthalpy curve at constant temperature without using a large amount of energy.

[0092] When the reservoir 100 is also the pressure reducing means 160 (see [Fig.l]), the compressed portion then circulates in the transfer pipe C11 which connects the compressor means 120 to the injector means 1008.

[0093] When the compressor means 120 is connected directly or indirectly to the pressure reducing means 160 located upstream of the injector means 1008 (see figures 2 and 3), the compressed portion then circulates in the transfer line C12 which connects the compressor means 120 to the pressure reducing means 160 or in the transfer line C13 which connects the compressor means 120 to the buffer tank 140.

[0094] In the case where the compressor means 120 is connected to the buffer tank 140, once the internal pressure of the buffer tank 140 reaches a predetermined pressure and preferably between 6 and 70 bar, the compressed portion which has been stored in the buffer tank 140 then circulates in the second transfer line C23 which leads to the pressure reducing means 160.

[0095] In a following step, the compressed portion then undergoes relaxation to obtain a relaxed portion defined at a state C by: - 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 lower than the second density D2 and higher than the first density DI.

[0096] According to the implementation of the exemplary embodiment illustrated in [Fig.l], the expansion takes place during or after the performance of a step of injecting the compressed portion into the reservoir 100, when the reservoir 100 is also the expansion means. In this case, the state C is defined as being the equilibrium state in the reservoir 100 after injection into the latter of the compressed portion. Here, the expansion can therefore be initiated during the injection and take place in the reservoir 100.

[0097] In this first embodiment illustrated in [Fig.l], the expansion is not isenthalpic. The portion injected into the reservoir 100 is also defined by a third enthalpy E3 which is lower than the first enthalpy El of the portion taken. This implies a reduction in the internal temperature of the reservoir 100 after thermodynamic equilibrium.

[0098] According to the implementation of the exemplary embodiments illustrated in Figures 2 and 3, the expansion takes place between the compression step and a subsequent step of injecting the expanded portion into the reservoir 100 when the installation comprises a pressure reducing means 160 separate from the reservoir 100. In this case, state C is defined as being the state in which the expanded portion is found before being injected into the reservoir 100. Thus, a portion leaving the expansion means 160 is obtained which has properties which approach the thermodynamic conditions of the reservoir 100.

[0099] According to the implementation of the exemplary embodiments illustrated in Figures 2 and 3, the expansion is preferably isenthalpic. Such an isenthalpic expansion has the advantage of not generating heat.

[0100] Preferably, in state C, the expanded portion is found substantially on the characteristic liquid saturation curve of the fluid. For example, in state C, P3 may be between PI and P2, preferably between PI and the liquid saturation pressure of the fluid to which 0.1 bar is added. Furthermore, by proceeding in this way, the injection into the reservoir 100 of the portion to be injected is facilitated.

[0101] The portion injected into the reservoir 100 is also defined by a third enthalpy E3 which is lower than the first enthalpy E1 of the portion taken. This implies a reduction in the internal temperature of the reservoir 100 after thermodynamic equilibrium. Thus, the portion injected into the reservoir 100 is, among other things, defined by a third temperature T3 lower than the first temperature T1 so as to compensate for any heating in the reservoir 100. By proceeding in this way, an increase in the pressure inside the reservoir 100 which would have been inevitable if the method according to the invention had not been implemented is therefore avoided. Examples

[0102] The storage installation according to the second embodiment example was implemented with hydrogen as fluid.

[0103] The table of experimental results below can be read in parallel with the diagram illustrated in [Fig.4] and in [Fig.5] with reference to the states A, B and C mentioned above.

[0104] As illustrated in [Fig.4], the enthalpy curve at constant temperatures of liquid hydrogen approximately equal to 30K has a substantially parabolic shape. In state B, we are at the inflection point of the enthalpy curve, the inflection point corresponding to a minimum of enthalpy over a pressure range between 8 bar and 30 bar.

[0105] As illustrated by [Fig.5], for hydrogen isenthalpic expansion can only be implemented above a pressure of 5 bar from which the Joules-Thomson coefficient becomes positive.

[0106] In particular, the table of experimental results below allows a better visualization of the advantages derived from the implementation of the method in accordance with the invention.

[0107] This table indicates values ​​of temperatures (in K), pressures (in bar), densities (in kg / m3), volumes (in m3 / kg), specific internal energy (kJ / kg) and enthalpies (kJ / kg) of hydrogen initially contained in the tank 100 and then circulating in the installation described above according to the method according to the invention described above so as to find itself in the states A, B, C mentioned above and which are found in [Fig.4].

[0108] [Tableauxl] State Temperature (K) Pressure (bar) Density (kg / m3) Volume (m3 / kg) Enthalpy (kJ / kg) A 30.2 8.5 53.37 0.019 149.02 B 30.2 23 60.39 0.017 138.83 C 29.8 8.5 54.93 0.018 183.83

[0109] The following information can be deduced from this table. Between states B and C, a substantially isenthalpic expansion has actually been implemented. Furthermore, in state C, the temperature T3 is much lower than the temperature T1 defined in state A. In this way, the density D3 defined in state C is much higher than the density DI defined in state A.

[0110] Of course, the invention is not limited to the particular examples described and illustrated in the present application. Other variants or embodiments within the reach of those skilled in the art may also be envisaged without departing from the scope of the invention, as defined by the claims.

Claims

1. Claims Method for controlling the internal pressure of a cryogenic tank (100) containing a liquid fraction (1002) and a gaseous fraction (1004) of a fluid whose enthalpy can decrease during isothermal compression in the liquid phase, the method comprising the following steps: - taking a portion of the liquid fraction to obtain a taken portion defined at a state A by: - a first temperature Tl, - a first pressure PI, - a first enthalpy El, and - a first density Dl, - substantially isothermal compression of the portion taken to obtain a compressed portion defined at a state B by: - a second temperature T2 substantially equal to the first temperature T1, - a second pressure P2 greater than the first pressure PI, and - a second density D2 greater than the first density Dl, said compression being intended to lead to a reduction in enthalpy between the first enthalpy El of state A and a second enthalpy E2 of state B, - relaxation of the compressed portion to obtain a relaxed portion defined at a state C by: - 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 lower than the second density D2 and higher than the first density D1, - injection of the compressed portion or the expanded portion into the reservoir (100), said expansion being carried out after the injection step when the compressed portion is injected into the reservoir (100), or said expansion being carried out between the compression step and the injection step when the expanded portion is injected in the tank (100).

2. A method according to claim 1, wherein the compression step results in a continuous decrease in the enthalpy of the portion taken from state A to state B.

3. A method according to claim 2, wherein the compression step is stopped when the enthalpy drop of the compressed portion is less than 0.1 kJ / kg for a pressure increase of 1 bar.

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

5. Method according to one of claims 1 to 4, according to which the third pressure P3 is greater than or substantially equal to the first pressure PI.

6. Method according to one of claims 1 to 5, according to which the expansion is a substantially isenthalpic expansion when it is carried out between the compression step and the injection step.

7. Installation for storing a liquid fraction (1002) and a gaseous fraction (1004) of a fluid configured to implement the method according to any one of claims 1 to 6, the installation comprising: - a cryogenic tank (100) intended to contain the fluid, - a means (1006) for withdrawing a portion of the liquid fraction (1002), - a compressor means (120) capable of carrying out a substantially isothermal compression of the withdrawn portion to obtain a compressed portion, the compressor means (120) containing a refrigeration unit, - an expansion means (160) capable of carrying out an expansion of the compressed portion to obtain an expanded portion, and - an injector means (1008) capable of injecting the compressed portion or the expanded portion into the cryogenic tank (100), installation in which the expansion means (160) and the tank (100) are either confused, or distinct.

8. Installation according to claim 7, further comprising a reservoir buffer (140) disposed between the compressor means (120) and the expansion means (160).

9. Installation according to one of claims 7 or 8, in which the pressure reducing means (160) comprises a throttle valve (162).

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