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, the enthalpy of which can be lowered during isothermal compression in the liquid phase.

Description

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 a facility for storing a cryogenic fluid.

[0002] A cryogenic tank means any tank suitable and designed to store gases in 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 facility.

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

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

[0008] For example, external supply elements include 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 vented to the atmosphere without being used. Conventionally, this evacuation is made possible by a protective device included in the tank such as a valve and / or a rupture disk allowing the release of at least a portion of the gaseous fraction to the outside in the event of pressure exceeding a limit in the tank. This limit is typically the maximum permissible 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] Therefore, 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 of consuming a portion of the liquid fraction contained in the tank so as to regularly lower the internal pressure of the tank, or of 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 in storage facilities.

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

[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 firstly proposed 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: - sampling a portion of the liquid fraction to obtain a sampled portion defined at a state A by: - ​​a first temperature T1, - a first pressure P1, - a first enthalpy E1, and - a first density D1, - substantially isothermal compression of the sampled portion 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 P1, and - a second density D2 greater than the first density D1,said compression being intended to lead to a reduction in enthalpies between the first enthalpy E1 of state A and a second enthalpy E2 of state B,- expansion of the compressed portion to obtain an expanded 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 expansion being carried out during or after the injection step when the compressed portion is injected into the tank, orsaid expansion being carried out between the compression step and the injection step when the expanded portion is injected into the tank.,

[0016] The method according to the invention makes it possible to counteract 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 step is stopped when the enthalpy decrease 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 P1,- the expansion is a substantially isenthalpic expansion when it is carried out between the compression step and the injection step.

[0018] Secondly, there is proposed an installation for storing a liquid fraction and a gaseous fraction of a fluid configured to implement the method described above, the installation comprising: - a cryogenic tank intended to contain the fluid, - a means for withdrawing a portion of the liquid fraction, - a compressor means comprising a compressor element and a cooling element of the compressor element configured to maintain the compressor element at temperature during the implementation of a compression in order to carry out a substantially isothermal compression of the withdrawn portion to obtain a compressed portion, - an expansion means capable of carrying out an expansion of the compressed portion to obtain an expanded portion, and - an injector means capable of injecting the compressed portion or the expanded portion into the cryogenic tank, installation in which the expansion means and the tank are either merged 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 expansion 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] This is a schematic representation of a storage installation according to a first exemplary embodiment of the invention.

[0024] This is a schematic representation of a storage facility according to a second exemplary embodiment of the invention.

[0025] This is a schematic representation of a storage facility according to a third exemplary embodiment of the invention.

[0026] This 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] This 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.

[0028] This is a schematic representation of an example of a compressor means for use in a storage facility according to an exemplary embodiment of the invention. Detailed description of the invention

[0029] In the following description, identical, similar or analogous elements will be designated by the same alphanumeric references.

[0030] The storage installation 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.

[0031] Tank 100 is a cryogenic tank.

[0032] The fluid is a cryogenic fluid.

[0033] The tank 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 tank 100 is preferably configured to store a volume of fluid of up to 50,000 L at an equilibrium temperature of between 3.15 K and 213.15 K, preferably between 18.15 K and 73.15 K.

[0034] 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.

[0035] Advantageously, the fluid is hydrogen. It should be noted that the temperature of liquid hydrogen is less than 33.15 K at atmospheric pressure.

[0036] For the purposes of the present invention, hydrogen means para hydrogen, ortho hydrogen or a mixture of the two.

[0037] 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 heat exchanges between the exterior of the tank 100 and the fluid.

[0038] The first envelope is preferably surrounded by a second envelope and the tank 100 comprises thermal insulation in the space between the two envelopes (in particular a vacuum space).

[0039] 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.

[0040] Conventionally, the tank 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 tank 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 particular if the method according to the invention malfunctions.

[0041] 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.

[0042] This reservoir 100 is further adapted to supply one or more liquid-requiring elements, preferably from a portion of the liquid fraction 1002 extracted from the bottom of the reservoir 100 (requiring elements not shown in the figures).

[0043] 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.

[0044] 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.

[0045] 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).

[0046] The tank 100 can therefore further comprise a supply circuit for the first envelope (supply circuit not shown in the figures).

[0047] 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.

[0048] The supply circuit may comprise a second supply line 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.

[0049] 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 merged.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] The storage facility 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 facility, 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 tank 100.

[0054] 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.

[0055] The storage facility further comprises a compressor means 120.

[0056] In an exemplary embodiment such as that illustrated in, the compressor means 120 is a compression equipment 200 which contains a compressor element 210 configured to carry out the compression and a cooling element 220 of the compressor element 210 which has the effect of cooling the compressor element 210 during the implementation of the compression, that is to say of maintaining the compressor element 210 at temperature while preventing it from heating up. This allows the compression equipment 200 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. In other words, the temperature of the portion of the liquid fraction entering the compression equipment 200 is approximately equal to that of the compressed portion leaving the compression equipment 200.

[0057] The compression equipment 200 is preferably configured to compress the portion of the extracted liquid fraction to a pressure of between 6 and 100 bar, at a temperature of between 18.15 K and 43.15 K. When the fluid is hydrogen, this pressure is preferably between 6 and 70 bar, or even between 6 and 40 bar, and at a temperature preferably between 28.15 K and 33.15 K.

[0058] Such compression equipment 200 then has the advantage of combining the compression and cooling functions in a single device.

[0059] The compressor element 210 of the compression equipment 200 is preferably a piston type pump, but may also be a gear, lobe, centrifugal, or other suitable pump configured to operate while submerged in a cryogenic liquid.

[0060] The cooling element 220 is preferably a device configured to cool the compressor element 210, in particular configured to cool the piston-type pump, during the performance of its compression. Preferably, as illustrated in the, the cooling element 220 is a storage device defining an interior volume comprising a lower section 221 and an upper section 222. This interior volume contains a volume of the portion of the liquid fraction 1002 taken, in particular which has been sucked by the pump but which has not yet passed through it and which is therefore not yet compressed. The volume of the portion of the liquid fraction 1002 taken contained in the storage device is sufficiently high to, preferably, cover the entirety of the lower section 221 in which the pump is located.In this way, the cold part of the pump is immersed in the volume of the portion of the liquid fraction 1002 which has been taken, while its hot part, which notably includes the transmission shaft 211, is placed outside this volume.

[0061] The storage device further comprises a supply line 223 for supplying the internal volume with liquid fraction 1002 which has been withdrawn. The supply line 223 may be the extraction line Cext or may be a separate line connected to the extraction line Cext. The supply line 223 is then connected to the withdrawal means 1006 and opens into the lower section 221 of the internal volume where an inlet E of the pump is preferably located. The inlet E of the pump is then arranged in contact with the bottom of the storage device, i.e. where the pressure is highest. The storage device also comprises an extraction line 212 connected to an outlet S of the pump through which the portion which has been compressed 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.

[0062] The storage device also comprises a degassing pipe 224 which opens into the upper section 222 of the interior volume.

[0063] In this embodiment, the liquid fraction 1002 taken, before passing through the pump, is then used as a refrigerant fluid and makes it possible to produce heat exchanges by direct contact with the pump in order to maintain it at temperature during compression. Having means which make it possible to induce heat exchanges directly at the pump, and not to apply them subsequently to the portion actually compressed, makes it possible to have a compact and simple-to-use compressor means.

[0064] Such a configuration has the effect of having a compact compressor means 120 in which the refrigerant fluid corresponds to that which was initially present in the tank 100 and which was taken via the taking means 1006. This allows obvious savings insofar as it is not necessary to bring a refrigerant fluid from outside.

[0065] In another exemplary embodiment, the cooling element is a refrigeration unit configured to produce heat exchanges with the compression element and in which circulates a refrigerant fluid different from that used in the example described above, and capable of cooling the compressor element during the implementation of the compression.

[0066] In another exemplary embodiment, the cooling element is a jacket (or casing) arranged on the periphery of the compressor element 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 jacket 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 jacket. Preferably, after the part of the portion of the extracted liquid fraction has circulated in the jacket, it is reintroduced into the reservoir 100 at its lower part. This also allows obvious savings insofar as it is not necessary to bring a refrigerant fluid from the outside.

[0067] In a first exemplary embodiment (exemplary embodiment shown in the), the compressor means 120 is connected downstream by a pipe C11 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.

[0068] 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.

[0069] 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 exemplary 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.

[0070] In a second exemplary embodiment (exemplary embodiment shown in the), 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 3.15 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 comprises a valve. For example, the valve may be a disc or porous orifice valve.

[0071] 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. This throttling valve may, for example, be a Joule-Thompson valve.

[0072] 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 higher than the expanded portion.

[0073] 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.

[0074] In a third exemplary embodiment (exemplary embodiment illustrated in the), the storage installation notably comprises the compressor means 120, the pressure reducing 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 C13.

[0075] The buffer tank 140 is connected downstream, by a second transfer line C23, to the pressure reducing valve means 160. The buffer tank 140 is therefore in particular arranged between the compressor means 120 and the pressure reducing valve means 160.

[0076] 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.

[0077] 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.

[0078] It should be noted that one or more of the pipes included in this storage installation may be equipped with at least one specific valve and / or a regulating means capable of controlling the flow of fluid circulating inside them.

[0079] Furthermore, one or more of the pipes included in this storage installation advantageously include thermal insulation envelopes (thermal insulation envelopes not shown in the figures).

[0080] As stated above, it should be noted that the storage facility is in a closed cycle.

[0081] 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).

[0082] 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 supply circuit. 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] After the sampling step, we thus obtain a sampled portion defined at a state A by:- a first temperature T1,- a first pressure P1,- a first enthalpy E1, and- a first density D1.

[0088] The sampled portion that 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.

[0089] 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.

[0090] 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 below a predetermined value, for example below 20 bar, preferably below 12 bar when the fluid is hydrogen.

[0091] 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.

[0092] 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, that is to say by a nominal flow rate.

[0093] 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 T1, - a second pressure P2 greater than the first pressure P1, and - a second density D2 greater than the first density D1.

[0094] 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 to the characteristics of the compressed fluid.

[0095] It should be noted that 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. Compression between state A and state B is substantially isentropic. This decrease in enthalpy is permitted because the Joule-Thomson coefficient (in K / bar) is positive for the predefined pressure range while 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 evolution of enthalpy (in kJ / kg) as a function of pressure (in bar) is negative. This compression is irreversible.

[0096] Advantageously, the compression step leads to a continuous decrease in the enthalpy of the portion taken from state A to state B.

[0097] 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 maximizes the efficiency of the installation.

[0098] However, the compression step is advantageously stopped when the enthalpy drop of the compressed portion is less than 0.1 kJ / kg for a pressure increase 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.

[0099] When the reservoir 100 is also the pressure reducing means 160 (see), the compressed portion then circulates in the transfer line C11 which connects the compressor means 120 to the injector means 1008.

[0100] 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.

[0101] 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.

[0102] In a following step, the compressed portion then undergoes expansion 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.

[0103] According to the implementation of the exemplary embodiment illustrated in the, 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.

[0104] In this first embodiment illustrated in the, 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 E1 of the portion taken. This implies a decrease in the internal temperature of the reservoir 100 after thermodynamic equilibrium.

[0105] 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 an expansion means 160 separate from the reservoir 100. In this case, the 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.

[0106] According to the implementation of the exemplary embodiments illustrated in Figures 2 and 3, the expansion is preferably isenthalpic. Such isenthalpic expansion has the advantage of not generating heat.

[0107] Preferably, in state C, the expanded portion is substantially on the characteristic liquid saturation curve of the fluid. For example, in state C, P3 may be between P1 and P2, preferably between P1 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.

[0108] 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.

[0109] The storage facility according to the second embodiment example was implemented with hydrogen as the fluid.

[0110] The table of experimental results below can be read in parallel with the diagram illustrated on the and on the with reference to states A, B and C mentioned above.

[0111] As illustrated in the, 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.

[0112] As illustrated by, for hydrogen isenthalpic expansion can only be implemented above a pressure of 5 bar from which the Joules-Thomson coefficient becomes positive.

[0113] 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.

[0114] This table shows values ​​of temperatures (in K), pressures (in bar), densities (in kg / m 3 ), volumes (in m 3 / 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 on the.

[0115] StateTemperature(K)Pressure(bar)Density(kg / m 3 )Volume(m 3 / kg)Enthalpy(kJ / kg)A30.28.553.370.019149.02B30.22360.390.017138.83C29.88.554.930.018183.83

[0116] The following lessons can be deduced from this table. Between states B and C, a substantially isenthalpic expansion has actually taken place. 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 D1 defined in state A.

[0117] 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

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 T1, - a first pressure P1, - a first enthalpy E1, and - a first density D1, substantially isothermal compression of the taken portion 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 P1, and - a second density D2 greater than the first density D1, said compression being intended to lead to a decrease in enthalpy between the first enthalpy E1 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 relaxed portion into the reservoir (100),said expansion being carried out after the injection step when the compressed portion is injected into the reservoir (100), orsaid expansion being carried out between the compression step and the injection step when the relaxed portion is injected into the reservoir (100)., The method of claim 1, wherein the compression step results in a continuous decrease in the enthalpy of the portion taken from state A to state B. Method according to claim 2, according to which 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. The method of claim 1, wherein the fluid is hydrogen. 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 P1. 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. 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) comprising a compressor element (210) and a cooling element (220) of the compressor element (210) configured to maintain the compressor element (210) at temperature during the implementation of a compression in order to carry out a substantially isothermal compression of the withdrawn portion to obtain a compressed portion, an expansion means (160) capable of carrying out an expansion of the compressed portion to obtain a relaxed portion, and an injector means (1008) capable of injecting the compressed portion or the portion into the cryogenic tank (100) relaxed,installation in which the pressure reducing means (160) and the tank (100) are either the same or separate. Installation according to claim 7, further comprising a buffer tank (140) disposed between the compressor means (120) and the expansion means (160). 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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