FR3032776A1 - MANAGEMENT OF FLUIDS IN A SEALED AND THERMALLY INSULATING TANK - Google Patents

Abstract

The invention relates to a method for the management of fluids in a sealed and thermally insulating tank (1) containing a liquefied gas (8) at low temperature, in which a wall of the tank has a multilayer structure comprising an outer bearing wall (2). , a primary sealing membrane (9) intended to be in contact with the liquefied gas contained in the tank, an intermediate space (3) situated between the primary waterproofing membrane and the outer supporting wall, the method comprising: sucking a gas phase of the intermediate space to the outside of the wall of the tank to lower the pressure in the intermediate space below a service pressure of the intermediate space, detect a stabilization of the pressure in the intermediate space during the suction step, warm the wall of the tank.

Description

TECHNICAL FIELD The invention relates to the field of sealed and thermally insulating vessels for the storage and / or transport of liquefied gases at low temperature, in particular in the field of membrane vessels.

BACKGROUND ART The mass volume of a gaseous body can be reduced to very high proportions by liquefaction of this body. It is therefore advantageous to store or transport the gases in a liquefied state at low temperature. For example, for liquefied natural gas (LNG), the mass volume is reduced by a factor of 600 between the gaseous state under normal conditions of temperature and pressure and the liquid state at about -163 ° C and at pressure atmospheric. Sealed and thermally insulating vessels are known whose wall has a multilayer structure comprising an outer supporting wall, a primary sealing membrane intended to be in contact with the liquefied gas contained in the tank, a secondary sealing membrane disposed between the outer bearing wall and the primary waterproofing membrane, a secondary space located between the secondary waterproofing membrane and the outer supporting wall, a primary space located between the secondary waterproofing membrane and the primary waterproofing membrane, and a barrier secondary insulation consisting of solid insulating materials disposed in the secondary space. In some tank structures, a primary insulating barrier is further disposed in the primary space. When the tank wall is in its normal operating state, the contents of the tank are thermally insulated from the outside by the superposition of the primary insulating barrier and the secondary insulating barrier. In case of invasion of the primary space by the liquefied gas contained in the tank, following a rupture or failure of the primary membrane, it remains the secondary insulating barrier for thermally insulating the bearing structure of this cold fluid, to prevent the carrier structure from reaching a temperature too cold to weaken, especially when it is the hull of a ship.

Other tank structures provide a very thin primary space with respect to the secondary space, so that the primary insulating barrier is suppressed or greatly reduced. Such vessels are for example disclosed in the publications FR-A-2709725, FR-A-2781036 and EP-A-1898143.

Advantages resulting from this choice are that the thermal insulation of the supporting structure is substantially the same in the normal operating state and in the case of invasion of the primary space by the liquefied gas. As a result, the materials of the load-bearing structure, especially the steel grades of the ship's hull, can be optimized. In addition, no component is likely to experience a thermal shock in the event of leakage of the primary membrane, since the thermal equilibrium is almost unchanged. It is therefore not necessary to size the secondary waterproof membrane in view of two operating points that are very different from one another, which simplifies the design and optimization of this membrane to withstand the stress in fatigue, for example the stresses caused by the elongation of the beam of the ship to the swell. SUMMARY An idea underlying the invention is to prevent the occurrence of a sudden overpressure in the primary space of a membrane vessel, particularly in the case of a tank where the primary space is very small. slim. Some aspects of the invention are based on the observation that any leakage of liquid or vapor through the primary waterproof membrane is likely to cause the presence of a liquid phase in a very thin primary space which is substantially at the temperature of the cargo. . This liquid phase will either be in the form of liquid and maintained on its equilibrium curve, or entered as vapor and condensed under the primary waterproof membrane, or, depending on the materials present in the primary space, entered under any form and adsorbed by solid materials having high adsorbency or capillarity capabilities. As such, plywood is a material commonly used in a thermally insulating barrier. For example, tests conducted in the laboratory show that such a material is likely to imbibe LNG. In the extreme case where the conditions of temperature and primary space pressure correspond to the two-phase equilibrium curve of methane and where liquid leakage occurs, the plywood can be charged from 18 to 20% by weight of LNG. When reheating a membrane vessel, the mass of gas present in the primary space in a condensed or adsorbed form by the wood will vaporize. In a system with reduced primary space, in which the pressure losses are very large, an overpressure may be formed in the primary space areas distant from the exhaust points. This pressure is liable to damage the primary barrier catastrophically and can therefore cause severe damage to the tank. The forces generated on the anchors linking the two barriers are, in certain configurations, likely to damage the secondary barrier itself creating channels of leakage, jeopardizing the integrity of the vessel carrying the tank. An object of the invention is therefore to provide a reheating procedure 15 which allows to heat the tank without risk of pressure increase of the primary space. Such a reheating procedure can be used in different circumstances, for example to perform a human technical intervention in the tank, for the regulatory inspection of the tank, maintenance or repair of an element of the tank. It can also be used to temporarily or permanently stop the operation of the tank. For this purpose, according to one embodiment, the invention provides a fluid management method in a sealed and thermally insulating tank containing a low temperature liquefied gas, in which a wall of the vessel has a multilayer structure comprising a load-bearing wall. external, a primary sealing membrane intended to be in contact with the liquefied gas contained in the tank, and an intermediate space located between the primary waterproofing membrane and the outer supporting wall, the method comprising: drawing a gaseous phase from the intermediate space to the outside of the wall of the vessel to lower the pressure in the interspace below a service pressure of the interspace, to detect a stabilization of the pressure in the interspace during the suction step, warm the wall of the tank.

The step of heating the wall of the tank may comprise the step of emptying the tank of its liquefied gas cargo at low temperature. Thanks to these characteristics, it is possible, at the time of reheating the tank wall, to force the vaporization of the liquid phase possibly accumulated in the intermediate space, in particular the primary space, or even of a solid condensed phase, in displacing the pressure prevailing in the intermediate space below the equilibrium point to the temperature considered, which is the temperature of the cargo in contact with the primary membrane. According to advantageous embodiments, such a method may have one or more of the following features. In one embodiment, suction of the gas phase is effected by means of a regulated vacuum pump to achieve a target pressure. Preferably, the difference between the predetermined target pressure and the service pressure of the intermediate space is greater than 10 kPa.

In one embodiment, the stabilization of the pressure in the interspace is detected after the pressure has ceased to evolve for a stability period greater than 1 hour, preferably greater than 2 hours. Qualitatively, the duration of stability must be longer as the free space of the intermediate space is large.

In one embodiment, the method further includes the step of selecting a reheat procedure based on the stabilized pressure in the interspace during the suction step. Thanks to these characteristics, it is possible to select a reheating procedure adapted to the conditions actually obtained in the intermediate space.

In one embodiment, a rapid reheat procedure is selected when the stabilized pressure in the interspace during the suction step is less than or equal to a predetermined threshold pressure lower than the operating pressure. The rapid reheat procedure may further include the step of injecting hot gas into the emptied tank of its liquefied gas cargo at low temperature, e.g., exhaust gases from a heat engine or gases heated by these by means of a heat exchanger or any other gas hotter than the ambient temperature.

In one embodiment, a slow reheat procedure is selected when the stabilized pressure in the interspace during the suction step is above a predetermined threshold pressure lower than the operating pressure. The slow reheat procedure may be to empty the tank slowly and / or allow the tank wall to naturally equilibrate with the ambient temperature as the tank is emptied. The slow reheat procedure may include the step of injecting a cold gas into the tank or spraying a stream of LNG or liquid nitrogen into the tank, particularly in the upper part of the tank, while the tank is emptied of its cargo of liquefied gas at low temperature. The cold gas may be dinitrogen or any other inert gas colder than the ambient temperature. Spraying a stream of liquefied gas makes it possible to slow down the natural rise in temperature more effectively by consuming the latent heat of vaporization of this stream. If necessary, it can be used for this a liquid nitrogen tank connected to the spray boom.

In one embodiment, the method further comprises: detecting the presence of a liquid phase in the interspace, maintaining suction of the gas phase in the interspace to substantially evaporate and / or desorb the entire phase liquid before warming the tank wall.

The detection of a liquid phase can be done in several ways. In one embodiment, the presence of a liquid phase is detected in response to a stabilization of the pressure in the intermediate space at an intermediate level between a predetermined target pressure and the operating pressure, and evaporation and / or Desorption of the entire liquid phase is detected in response to a subsequent decrease in the pressure in the intermediate space below the intermediate level. In one embodiment, the detection of a liquid phase comprises: measuring the temperature in the interspace for a period of time from the lowering of the absolute pressure in the interspace, detecting a liquid phase in response to a stabilization of the temperature in the intermediate space in the vicinity of the liquid-vapor equilibrium point of the liquefied gas for a predetermined target pressure, and detecting an evaporation and / or desorption of the entire liquid phase in response to a stabilization of the temperature in the intermediate space in the vicinity of the temperature of the liquefied gas contained in the tank. Thanks to these characteristics, it is determined whether the fluid in the intermediate space behaves as a diphasic equilibrium at the pressure considered, or if it is in thermal equilibrium with its environment independently of the pressure imposed on it. In one embodiment, lowering the pressure in the intermediate space comprises: lowering the pressure in the interspace to a first pressure threshold below the operating pressure, measuring a first temperature in the space; intermediate space after the pressure drop to the first pressure threshold, lowering the pressure in the intermediate space to a second pressure threshold lower than the first pressure threshold, measuring a second temperature in the intermediate space to successive instants after the pressure drop to the second pressure threshold, determine a difference between the second temperature and the first temperature, maintain the suction and delay the reheating of the tank as the difference between the second temperature and the first temperature is not below a predetermined temperature threshold, select the reheat procedure after the the difference between the first temperature and the second temperature has fallen below the predetermined temperature threshold. The slow or fast procedure can be selected depending on the stabilized pressure.

In one embodiment, the slow reheat procedure is selected if the difference between the second temperature and the first temperature has not become less than a predetermined temperature threshold after a predetermined maximum suction time. Such a state may mean that a very large liquid phase inlet may exist through the primary membrane, so that the reheating of the vessel must be accompanied by safety measures. In one embodiment, the intermediate space comprises a secondary sealing membrane disposed between the outer supporting wall and the primary sealing membrane, a secondary space located between the secondary sealing membrane and the outer supporting wall, a primary space located between the secondary waterproofing membrane and the primary waterproofing membrane, and a solid secondary insulating barrier disposed in the secondary space, a thickness of the primary space is much less than a thickness of the space secondary pressure and the primary space so that the pressure difference between the secondary space and the primary space remains below a safety threshold, and the stabilizing the pressure at least in the primary space to select the reheating procedure as a function of the stabilized pressure in the primary space. In one embodiment, the pressure in the secondary space is lowered below the pressure in the primary space. The invention also provides a fluid management device for a sealed and thermally insulating vessel for containing a low temperature liquefied gas, wherein a wall of the vessel has a multilayer structure having a carrier wall, an outer wall, a d primary seal intended to be in contact with the liquefied gas contained in the tank, an intermediate space located between the primary waterproofing membrane and the outer supporting wall, the fluid management device comprising: pressure sensors for measuring the pressure in the intermediate space, a vacuum pump connected to the intermediate space for sucking a gaseous phase from the intermediate space to the outside of the wall of the tank and able to lower the pressure in the intermediate space by below a service pressure of the intermediate space, a control module able to detect a stabilization of the ssion in the intermediate space during the suction step and to select a reheating procedure according to the stabilized pressure in the intermediate space 30 during the suction step. Such a device can be used to implement the aforementioned methods. According to advantageous embodiments, such a device may have one or more of the following characteristics.

In one embodiment, the device further comprises temperature sensors for measuring the temperature in the intermediate space, and the control module controls the vacuum pump and the temperature sensors to: reduce the pressure in the intermediate space up to a first pressure threshold lower than the operating pressure, measuring a first temperature in the intermediate space after the pressure drop to the first pressure threshold, lowering the pressure in the intermediate space to a second pressure threshold lower than the first pressure threshold, measuring a second temperature in the intermediate space at successive instants after the pressure drop to the second pressure threshold, determining a difference between the second temperature and the first temperature, maintain the suction and delay the reheating of the tank as the gap between the second tempe and the first temperature is not lower than a predetermined temperature threshold, select the fast reheat procedure after the difference between the first temperature and the second temperature has fallen below the predetermined temperature threshold.

In one embodiment, the intermediate space comprises a secondary sealing membrane disposed between the outer supporting wall and the primary sealing membrane, a secondary space located between the secondary sealing membrane and the outer supporting wall, a primary space located between the secondary waterproofing membrane and the primary waterproofing membrane, and a secondary solid insulating barrier disposed in the secondary space, the thickness of the primary space is much less than a thickness of the space secondary, and the vacuum pump is connected at least to the primary space, the control module being able to detect the pressure stabilization at least in the primary space to select the heating procedure according to the stabilized pressure in the primary space. In one embodiment, the device further comprises a fluid connection connecting the secondary space to the primary space, the fluid connection comprising a valve closed by default and able to open in response to a differential of 3032776 9 pressure greater than a predetermined opening threshold between the secondary space and the primary space. In one embodiment, a first vacuum pump is connected to the primary space and a second vacuum pump connected to the secondary space. In another embodiment, a vacuum pump is connected parallel to the primary space by a first suction line and to the secondary space by a second suction line, each suction line being provided with a body of loss of load. A tank equipped with such a fluid management device can be part of an onshore storage facility, for example to store LNG or be installed in a floating structure, coastal or deep water, including a LNG tanker, ethanier , a floating storage and regasification unit (FSRI I), a floating production and remote storage unit (FPSO) and others. According to one embodiment, a vessel for the transport of liquefied gas comprises a double hull and a said tank disposed in the double hull. According to one embodiment, the invention also provides a method for loading or unloading such a vessel, in which a fluid is conveyed through isolated pipes from or to a floating or land storage facility to or from the tank of the vessel. ship.

According to one embodiment, the invention also provides a transfer system for a fluid, the system comprising the abovementioned vessel, insulated pipes arranged to connect the vessel installed in the hull of the vessel to a floating storage facility or and a pump for driving fluid through the insulated pipelines from or to the floating or land storage facility to or from the vessel vessel. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood, and other objects, details, features and advantages thereof will become more clearly apparent from the following description of several particular embodiments of the invention, given solely to illustrative and non-limiting, with reference to the accompanying drawings. FIG. 1 is a diagrammatic cross-sectional view of a sealed and thermally insulating tank equipped with a fluid management device according to one embodiment; FIG. 2 is a diagram of steps of a process; 5 is a step diagram of a management method that can be used in the tank of FIG. 1 according to a second embodiment. FIG. 4 is a diagram showing complementary steps of the management method of FIG. 3; FIG. 5 is a diagram illustrating pressures measured in the tank of FIG. 1 in a normal operating state; FIG. 6 is a diagram illustrating pressures measured in the tank of FIG. 1 in a leakage state of the carrier wall; FIG. 7 is a diagram illustrating pressures measured in the tank of FIG. 1 is a diagram illustrating pressures measured in the tank of FIG. 1 in a state of leakage of the primary membrane and without this leakage, FIG. 9 is a diagram illustrating the pressures measured in the tank of FIG. a step diagram of a management method that can be used in the tank of FIG. 1 according to a third embodiment; FIG. 10 is a diagram showing complementary steps of the management method of FIG. 9; FIG. 11 is a diagram illustrating pressures measured in the tank of FIG. 1 during the management process of FIG. 9; FIG. 12 is a diagram illustrating temperatures measured in the tank of FIG. 1 during the process; FIG. 13 is a partial view of the fluid management device of FIG. 1 in a variant, FIG. 14 is a partial view of the fluid management device of FIG. 1 according to another variant, - Figure 15 is a bottom view of a primary insulating barrier element that can be used in the tank of Figure 1; 5 - Figure 16 is a partial cross-sectional view of a wall; FIG. 17 is a cutaway schematic representation of a tanker vessel equipped with a tank and a loading / unloading terminal of this tank.

DETAILED DESCRIPTION OF THE EMBODIMENTS In the description of the claims, the term "gas" has a generic character and refers equally to a gas consisting of a single pure substance or a gaseous mixture consisting of a plurality of components. A liquefied gas thus refers to a chemical body or a mixture of chemical bodies which has been placed in a liquid phase at low temperature and which would occur in a vapor phase under normal temperature and pressure conditions. In FIG. 1, a sealed and thermally insulating tank 1 for the storage and transport of a liquefied gas is shown. Such a tank 1 can be installed on the ground or on a floating structure. In the case of a floating structure, the tank may be installed in the hull of a liquefied natural gas transport vessel, such as an LNG tanker, but may also be intended for any vessel whose powertrain or generator sets , the steam generators or any other consumer member are supplied with gas. By way of example, it can thus be a goods transport vessel, a passenger transport vessel, a fishing vessel, a floating power generation unit or the like. . The tank 1 is a membrane tank whose walls have a multilayer structure comprising, from the outside towards the inside of the tank 1, a carrier wall 2, which is for example the inner wall of the double hull of the vessel, a secondary space 3 comprising secondary insulating elements 4 resting against the supporting wall 2, a secondary sealing membrane 5 resting against the secondary insulating elements 4, a primary space 6 possibly comprising solid elements 7 resting against the membrane of secondary seal 5 and a primary sealing membrane 9 intended to be in contact with the liquefied gas 8 contained in the tank. Such a vessel may in particular have a parallelepipedal, prismatic or polyhedral shape. The tank 1 represented in FIG. 1 has a primary space 6 of small thickness, and therefore of small volume, filled with solid modular elements 7 of small thickness which can fulfill a function of thermal insulation, a transmission function of the forces and / or mechanical protection against perforation of the secondary sealing membrane 5. The solid modular elements 7, as well as the secondary insulating elements 4, can be made of different materials, for example plywood, polymer foam, glass wool or rock, expanded perlite, airgel, balsa and other insulating materials. Alternatively, the primary space 6 may also be a void space between the two watertight membranes, devoid of any solid material. An example of such a primary space is provided in EP-A-1898143. Liquefied gas 8 is a cold product that can vaporize on reheating to room temperature. The liquefied gas 8 may in particular be a liquefied natural gas (LNG), that is to say a gaseous mixture comprising mainly methane and one or more other hydrocarbons, such as ethane, propane -butane, i-butane, n-pentane, i-pentane, neopentane, and nitrogen in a small proportion. The liquefied gas 8 may also be ethane or a liquefied petroleum gas (LPG), i.e. a hydrocarbon mixture derived from petroleum refining essentially comprising propane and butane. The liquefied gas 8 may also be nitrogen, helium, ethylene or liquid hydrogen. The liquefied gas 8 is stored in the interior space of the vessel in a two-phase equilibrium liquid-vapor state. The gas is thus present in the form of a vapor phase in the upper part of the vessel. The equilibrium temperature of the liquefied natural gas corresponding to its two-phase liquid-vapor equilibrium state is about -162 ° C when stored at atmospheric pressure.

During its operation, the tank 1 is inevitably subjected to large temperature variations. In particular, after the tank 1 has been operated to transport or store the liquefied gas 8, it may be necessary to completely empty and then reheat the tank 1 to room temperature, or because there is no immediately available cargo to be stored or transported in the tank 1, or because a repair or maintenance intervention requires the introduction of personnel and / or tools in the tank 1. The vessel 1 of Figure 1 is equipped one or more pressure sensors 41 for measuring the pressure in the primary space 6, one or more pressure sensors 42 for measuring the pressure in the secondary space 3, of one or more temperature sensors 45 for measuring the temperature in the primary space 6, one or more temperature sensors 46 for measuring the pressure in the secondary space 3. The purpose of these sensors will appear in the description of the methods below.

Procedures that can be used to safely reheat the vessel 1 will now be described, avoiding generating unacceptable overpressures in the primary space 6. It should be noted that the variation of the pressure caused by a gas flow introduced into the a given closed space is even faster than the volume of this space is small. Thus, the risk of an overpressure appearing suddenly in the primary space due to the vaporization of a certain amount of gas from its liquid phase is higher in a small volume primary space. Nevertheless, the procedures described below can be used in any membrane tank regardless of the volume of the primary space.

Referring to Fig. 2, a reheat procedure according to a first embodiment will be described. For purposes of illustration, the tank 1 is supposed to initially contain a cargo of LNG stored at a tank pressure close to atmospheric pressure, so that the liquid-vapor equilibrium point is close to -162 ° C. The tank pressure here refers to the absolute pressure prevailing in the vapor phase at the top of the tank 1, and which therefore determines the diphasic equilibrium temperature in the tank 1. It may differ from the atmospheric pressure by a few tenths of kPa more or less, within the limits of resistance of the waterproofing membranes.

The actual content of the primary 6 and secondary 3 spaces is not precisely known at the beginning of the reheating procedure, so that the existence of a possible liquid phase capable of vaporizing during the reheating procedure is neither certain nor excluded. However, except for the presence of 5 leaks in the primary membrane 9 or in the carrier wall 2, the primary 6 and secondary 3 spaces are assumed to initially contain a gaseous phase at a pressure close to the tank pressure. In step 11, the reheating procedure is initiated in order to empty the tank and warm the walls of the tank. In step 12, the secondary space 3 is depressurized by means of a vacuum pump 22 arranged to pump the gas phase into the secondary space 3 and reject the pumped gas outside the wall. tank, for example in the ambient air, in a steam vessel of the vessel or in the vessel 1. In step 13, the primary space 6 is put under vacuum using a vacuum pump 21 arranged for pumping the gas phase into the primary space 6 and rejecting the pumped gas outside the vessel wall, for example in ambient air, in a ship's steam manifold or in vessel 1. Vacuum pumps 21 and 22 are implemented so as to effect a regulation of the absolute pressure in the primary space 6 and the secondary space 3 respectively. For this purpose, target pressures are set: namely a primary target pressure Po-dp1 for the primary space 6 and a secondary target pressure Po-dp2 for the secondary space 3, where Po denotes the close vat and dp1 and dp2 are positive values. The purpose of the depression -dp1 is to displace the liquid-vapor equilibrium which has possibly been established in the primary space 6, for example if leakage of the liquefied gas 8 is introduced therein or if other gaseous substances are introduced. have condensed therein or have been adsorbed therein, so as to cause forced vaporization of the liquid phase. Depression -dp1 must be high enough for this vaporization to have sufficient kinetics. Preferably dp1 is about 10 to 50 kPa, for example about 20 kPa. As the vacuum pump 21 regulates the pressure in the primary space 6 to establish and maintain the primary target pressure Po-dp1, the vacuum pump 22 regulates the pressure in the secondary space 3 for establish and maintain the secondary target pressure Po-dp2. The main purpose of the -dp2 depression is to maintain a relative pressure balance across the secondary diaphragm 5, since the secondary diaphragm 5 is not normally able to withstand a high pressure differential. . Thus, the target pressures must satisfy the relation: Idp1-dp2I <DP, where DP denotes a predetermined safety threshold guaranteeing the integrity of the secondary membrane 5. Preferably, DP is between 0.5 kPa and 4 kPa, for example equal to 2kPa. Preferably, the target pressures also satisfy the relation: dp2> dp1, so that the pressure difference on either side of the secondary membrane 5 tends to press it against the secondary insulating barrier and not on the other side. tear off the secondary insulating barrier. The vacuum pumps 21 and 22 are cryogenic pumps, that is to say able to withstand cryogenic temperatures below -150 ° C. They are also compliant with the ATEX regulations, that is to say designed to avoid any risk of explosion. The vacuum pumps can be made in various ways, for example Roots (ie rotating lobes), vane, liquid ring, screw, with a venturi type effector. Vacuum pump suppliers are, for example, MPR Industries or Busch Group. The regulation of the absolute pressure by the vacuum pumps 21 and 22 in the primary space 6 and the secondary space 3 can be started simultaneously or sequentially and is maintained for a period of time sufficient for the pressures to stabilize at the same time. target pressures and remain stable for a predetermined stability period, as indicated in step 14. According to one embodiment, particularly if there is no way to detect the presence or absence of liquid phase. in the primary space 6, the stability period is chosen relatively long, to allow the vaporization of the entire liquid phase may exist with a large margin of safety. The duration of stability can thus be of the order of several hours, for example between 2h and 10h. Conversely, a shorter stability time may be chosen if detection of the liquid phase is also carried out, as will be explained below.

At the end of the stability period, step 15 consists in carrying out the emptying and reheating of the tank 1. The reheating can be implemented simply by placing the emptied tank in communication with the atmosphere. ambient, or by injection of hot gas into the tank to accelerate the heating, for example combustion gases from a heat engine. The pressure regulation by the vacuum pumps 21 and 22 is preferably continued during step 15. This precaution makes it possible to continue to vaporize a possible flow of liquid entering the primary space 6 because of a leakage leakage of the primary membrane 9. FIG. 5 illustrates an exemplary embodiment of the above method, in the case where the depressions dp1 and dp2 are equal to 20 kPa. FIG. 5 is a diagram representing the absolute pressure expressed in kPa on the ordinate axis and the time expressed in second on the abscissa axis. Curve 16 represents the pressure in the primary space and curve 17 represents the pressure in the secondary space. In this example, the pressures 16 and 17 effectively achieve the desired target pressures, which means that there is no seal defect. In practice, the detection that the desired pressure has actually been reached consists of detecting the crossing from below of a detection threshold having a positive tolerance deviation with the reference pressure of the vacuum pump. This tolerance difference is small compared to dp1 and dp2, typically between 0.1 and 1 kPa. It can be more precisely fixed according to the structural characteristics of the tank, in particular as a function of the pressure drop between the inlet of the vacuum pump and the pressure sensor on the one hand, and the stability period of 'somewhere else. The procedure described above can be carried out under the control of an electronic control device 50, for example a programmed computer. For this purpose, the control device 50 is connected to the pressure sensors 41 and 42 via links 43 and 44, in order to acquire pressure measurements over time, and to the vacuum pumps 21 and 22 via links 23 and 24, to control the vacuum pumps 21 and 22 over time. Step 11 can be triggered manually, for example by actuating a controller of a man-machine interface not shown, or automatically, for example by receiving an instruction from a central computer system not represent.

In the example above, it was assumed that the primary space 6 was initially at the tank pressure Po of the tank 1. In an alternative embodiment, the primary space 6 is initially in depression, that is, the operating pressure Ps in the primary space 6 is already lower than the tank pressure Po of the tank 1 when the tank is full of its cargo. In this case, if there is accidentally a liquid phase in the primary space 6, it is at equilibrium at the pressure Ps. The vaporization of this liquid phase can therefore be forced in the same way by lowering the pressure below the operating pressure Ps. The above method is therefore also usable in this case by using for the primary space 6 a target pressure Ps-dp1 and for the secondary space 3 a target pressure Ps-dp2 . The method described above is also adaptable to a tank having a single sealed membrane, for example when the secondary membrane 5 is removed or replaced by a self-supporting waterproof envelope capable of withstanding a pressure difference. In this case, step 12 can be deleted. The procedure of FIG. 2 is a vacuum bleed procedure which does not make it possible to discriminate anomalies such as leakage of the primary 9 or secondary 5 waterproof membrane. Moreover, the presence of safety margins important in the stability period does not optimize the duration of the procedure. Thus, a procedure also for detecting a leakage of the primary membrane 9, the secondary membrane 5 or the carrier wall 2 may be preferred. In addition, a procedure which also makes it possible to detect the presence of liquid gas or absorbed by materials in the primary space 6 may also be preferred.

Figs. 3 and 4 show a reheat procedure according to a second embodiment which meets these needs. The first two steps 11 and 12 are unchanged compared to FIG. 2. In step 25, the evolution of the pressure in the secondary space 3 is monitored using the pressure sensor 42, to determine whether the pressure converges to the expected target pressure Po-dp2. If this test is satisfied, which is true, for example, in the example of FIG. 5, the method proceeds to step 13 which is unchanged with respect to FIG. 2. Otherwise, the process proceeds to FIG. described below.

The test of step 25 is useful to avoid damaging the secondary membrane 5 in the event of leakage of the carrier wall 2. This case is explained with reference to FIG. 6. FIG. 6 is a diagram 5 is an example of embodiment of the method, in which the depressions dp1 and dp2 are equal to 20 kPa and a substantial leakage of the carrier wall 2 exists. Curve 117 is a reference curve representing the expected pressure evolution in secondary space 3 under normal operating conditions. Curve 117 converges rapidly towards the target pressure Po-dp2. Curve 17 represents the pressure actually measured in the secondary space 3. In this case, it stabilizes significantly above the target pressure, due to a permanent leakage rate through the load-bearing wall 2. this leakage, there is the risk that the secondary space 3 contains large amounts of gas absorbed by the secondary insulating elements 4, which may suddenly vaporize during heating and damaging the sealed membranes. For this reason, when the test of step 25 is not satisfied after a certain monitoring period, the method of FIG. 4 is executed. With reference to FIG. 4, step 31 consists in modifying the primary target pressure to make it compatible with the pressure P0-52 actually measured in the secondary space 3. In other words, the value dp1 is modified to satisfy: Idp1-82I <DP. Step 32 is equivalent to step 13 above, but with the new target pressure Po-dp1. The curve 16 of FIG. 6 thus represents the pressure measured in the primary space 6 during the procedure. In view of the lesser depression, step 32 can not ensure evacuation of the eventual liquid phase with the same degree of safety as in step 13. Step 33 finally consists in carrying out the emptying and reheating of the tank 1, but with slow kinetics taking into account the risks of a sudden vaporization of products in the secondary space and / or the primary space. The slow reheat procedure includes, for example, an LNG spraying from the cargo in the vessel 1 during all or part of the emptying and reheating time.

Returning to FIG. 3, when step 13 is carried out, step 26 consists in monitoring the evolution of the pressure in the primary space 6 by means of the pressure sensor 41, in order to determine if the pressure converges to the expected target pressure Po-dp1. If this test is satisfied, which is true, for example, in the example of FIG. 5, the process proceeds to step 15 which is unchanged from FIG. 2. If not, the method proceeds to step 27 The test of step 26 is useful for determining whether there is a leak in the primary diaphragm 9. This case is explained with reference to Figure 8. Figure 8 is a diagram similar to Figure 5 showing an example of carrying out the process, wherein the depressions dp1 and dp2 are equal to 20 kPa and a substantial leakage of the primary membrane 9 exists. Curve 116 is a reference curve representing the expected pressure evolution in primary space 6 under normal operating conditions. Curve 116 converges rapidly towards the target pressure Po-dp1. Curve 16 represents the pressure actually measured in the primary space 6. In this case, it is significantly stabilized above the target pressure, due to a constant leakage rate through the primary membrane 9. of this leakage, there is a risk that the primary space 6 may contain significant amounts of liquid phase and / or gas absorbed by the primary insulating elements 7, which may vaporize it suddenly during heating and damage. waterproof membranes. For this reason, when the test of step 26 is not satisfied after a certain monitoring period, step 27 is performed. Step 27 consists in analyzing the evolution curve of the pressure measured in the primary space 6 to detect whether an intermediate stabilization plateau has been crossed. Curve 16 of FIG. 8 illustrates such an evolution. This curve 16 shows that before finally stabilizing at a value close to 90 kPa beyond the instant 27000s, the pressure in the primary space 6 has temporarily stabilized between the instant 15000s and the instant 20000s forming a plateau at an intermediate value Pi between the initial pressure and the final stabilization pressure, close to 97 kPa. The existence of such a plateau means that a steady stream of gas has been generated during this period under the effect of the depression in the primary space 6, either by vaporization of an accumulated liquid phase or by desorption of an absorbed phase. Passing this plateau and stabilizing the pressure to a lower level therefore means that this liquid or absorbed phase has been further evaporated and that reheating can now be done, slowly or rapidly depending on whether or not it exists. a leak in progress. For this, the process returns to step 26 as indicated by arrow 28. In the example of curve 16 of FIG. 8 in solid line, the final stabilizing pressure is substantially greater than the target pressure, which means that there is a permanent leakage rate. The stabilization pressure results from the equilibrium between the pumping rate and the leakage rate. The slow reheat procedure must be continued in this case, that is, when the pressure is stabilized and the process returns to step 27.

In FIG. 8, the dot-dashed curve 216 illustrates another case in which an amount of condensed or adsorbed liquid phase was stored in the primary space without there being a permanent leakage rate. After crossing the vaporization plate, the pressure finally stabilizes at the target pressure. The process proceeds to step 15 which is unchanged from FIG. 2.

The existence of a stock of condensed or adsorbed gases in the primary space without leakage flow in the membranes can have different causes. For example, this stock may be due to a faulty or poorly tuned scavenging gas generator, which instead of generating a stream of pure dinitrogen introduces significant amounts of other gases into the primary space, for example carbon dioxide. carbon, oxygen or other impurities. Another possible source of the impurity stock is the solids introduced into the primary space for insulation or structural reinforcement purposes, for example foamed polymers loaded with blowing agents which have been released by diffusion into the primary space. during the operating life of the tank. After an operating period of several months or years, such phenomena are likely to generate substantial stocks of gaseous bodies condensed or adsorbed in the primary space. In some cases, there may be several successive stabilization trays before the final stabilization of the pressure, for example for particular pairs of adsorbent-adsorbed materials. Conversely, if the pressure drops directly to the final stable value without marking a plateau, it means that there is no substantial amount of product in the liquid phase or absorbed to evaporate. In all cases, it is the level of the final stabilized pressure that makes it possible to select the normal reheating procedure or the slow procedure. However, a relatively long stabilization time must be observed to ensure that the final pressure has indeed been reached. A faster and more certain procedure for detecting the presence of a liquid phase can therefore be to monitor also the evolution of the temperatures, as will be explained below. In the foregoing explanations, the case of a defect of the secondary membrane 5 has not been addressed. Indeed, such a defect is only likely to modify the kinetics of evolution of the pressures in the primary and secondary spaces under the action of the vacuum pumps and does not in itself prevent the descent of the pressures towards the target pressures, and more especially towards the lowest target pressure. This case is illustrated in FIG. 7. FIG. 7 is a diagram 10 similar to FIG. 5 showing an exemplary embodiment of the method, in which the depressions dp1 and dp2 are equal to 20 kPa and a substantial leakage of the secondary membrane 5 exists. Curve 117 is a reference curve representing the expected pressure evolution in secondary space 3 under normal operating conditions. Curve 117 converges rapidly to the target pressure Po-dp2. The curve 17 represents the pressure actually measured in the secondary space 3. The curve 16 represents the pressure actually measured in the primary space 6. Due to the communication between the two spaces, the vacuum pump 22 lowers the pressure in secondary space 3 slower than expected. In an alternative embodiment, step 25 is modified to also detect the existence of a defect in the secondary waterproof membrane 5. For this, a comparison between the time derivative of the measured pressure 17 and the reference 117 is performed. For the rest, the procedure is unchanged. The reference curves 116 and 117 are plotted when the state of operation of the tank 1 has just been checked, for example when the ship is in a new condition. With reference to FIGS. 9 to 12, a reheat procedure according to a third embodiment will now be described wherein temperature measurements are employed to detect the presence of a liquid phase in the primary space 6. The The purpose of the procedure is to evaluate the local behavior of the fluid present in the primary space 6. In order to obtain information on the nature of the fluid at a given point, the procedure consists of reducing the pressure and following the evolution of the temperatures. A lowering of the pressure is supposed to produce a cooling of the vapor phase by expansion. However, taking into account the large exchange surface of the primary membrane 9 with the liquid cargo 8, the cooled vapor in the primary space immediately tends to heat up to the temperature of the cargo 8 By contact with the primary membrane 9. Thus, if, following a lowering of the pressure, the temperature returns in a few minutes to its initial temperature, then the fluid in the primary space 6 is in the vapor phase. If, on the other hand, the temperature tends towards the equilibrium temperature of the liquid at the considered lowered pressure, then the primary space contains a non-zero liquid fraction, at least in the vicinity of the point of measurement of the temperature. An array of temperature and pressure sensors 10 distributed on the walls of the tank 1 is therefore necessary to be able to take local measurements in different zones of the walls of the tank 1. FIG. 9 describes a method of managing the pressures and acquisition of measures. FIG. 11 is a diagram representing the absolute pressure expressed in kPa on the ordinate axis and the time expressed as second on the abscissa axis, on which the curves 16 and 17 represent the pressure measured respectively in the primary space 6 and the secondary space 3 during the process of FIG. 9. FIG. 12 is a diagram representing the temperature expressed in degrees Celsius on the ordinate axis and the time expressed as the second on the abscissa axis, on which the curves 39 and 40 represent the temperature measured in the primary space 6 during the process of FIG. 9, respectively in the absence and in the presence of a liquid phase to be vaporized. In step 51, the pressure in the secondary space is lowered by a small difference Rs, for example of the order of 1 kPa, so that the pressure can be lowered similarly in the primary space without generating excessive forces on the secondary membrane 5. In step 52, the pressure in the primary space is lowered by a small gap Rp, where RpERs. In step 53, a certain amount of time elapses to allow the temperature of the vapor phase in the primary space 6 to stabilize. In step 54, a reference temperature measurement Tr is acquired in the primary space 6, normally reflecting a small cooling compared to the initial temperature and a return to equilibrium even faster than the mass of liquid phase is low. In step 55, the pressure in the secondary space is lowered by a large difference Qs, for example of the order of 20 kPa, so that the pressure can be lowered similarly in the primary space without generating Excessive forces on the secondary membrane 5. In step 56, the pressure in the primary space is lowered by a large difference Qp, where Qp_Qs. In step 57, a certain time elapses to allow the temperature of the vapor phase to stabilize in the primary space 6. In step 58, a second temperature measurement Tm is acquired in the primary space 6 Figure 10 depicts a method of processing temperature measurements. In step 61, the two-phase equilibrium temperature of the liquefied gas under pressure (Po-Rp), denoted Te, is determined. In step 62, a positive threshold proportional to ITe-Tri is calculated, denoted E. At step 63, the following inequality is tested: ITm-Tr15.c If the inequality is verified, which means that the temperature has equilibrated substantially at the same level as a result of the small pressure difference and following the large pressure difference, the method results in the detection of a dry vapor phase at the measuring point, Step 65. This case corresponds to the curve 39 of Figure 12. The reheating can then be undertaken immediately without risk. If the inequality is not satisfied, which means that the temperature has equilibrated at substantially different levels as a result of the small pressure difference and following the large pressure difference, the process proceeds to step 64 where the diphasic equilibrium temperature of the liquefied gas under pressure (PoQp), denoted Tf, is determined. In step 66, the following inequality is tested: iTf-Tml5E If the inequality is satisfied, which means that the temperature has equilibrated substantially at the point of equilibrium at the lowered pressure, the process succeeds. detection of a liquid phase during vaporization at the measurement point, at step 68. This case corresponds to curve 40 of FIG. 12. If the inequality is not verified, a rate of stabilization r is calculated in step 67 according to the formula: = (Tm -Tf) / (Tr -Tf) The depression must then be maintained in the primary space prior to reheating of the tank, for a duration of as much longer 3032776 24 than this stabilization rate is low. In FIG. 12, the reheating can be started from the moment when the curve 40 has come close enough to the temperature Te, for example from the instant 20000. The method described above can be carried out simultaneously or sequentially in all measurement areas covered by the sensor array. The procedure of the third embodiment makes it easy to map areas containing a liquid fraction. By successive measurements, it is possible to follow the evolution of the liquid content of the primary space. The reheating procedures according to the second and third embodiments therefore make it possible to check the integrity of the storage system. They can be carried out jointly in order to obtain macroscopic information on the state of the tank as well as information on the evolution of the condensate content or the progress of the purge of the primary space at different points of the tank. primary space. These can also be implemented under the control of the electronic control device 50. Advantageously, when the secondary membrane 5 is made of heat-conducting materials, for example metallic, the temperature sensors intended for measurement in the primary space 6 are arranged under the secondary membrane 5 in order to limit the crossings thereof. It is however necessary to limit the contact resistance between the temperature sensor and the secondary membrane 5. In other embodiments shown in FIGS. 13 and 14, a single vacuum pump is employed for primary and secondary spaces.

FIG. 13 thus represents a partial view of the vessel wall equipped with a connecting device 35 establishing a fluid connection between the secondary space 6 and the primary space 3. The connection device 35 comprises a calibrated valve 36 presenting a closed state by default and is likely to open when the pressure in the secondary space 6 exceeds the pressure in the primary space 3 by a value greater than a given threshold. The opening threshold is preferably between 1 and 5 kPa, for example equal to 3 kPa. In this case, the vacuum pump 22 can be omitted and the methods described above can be simplified, since the pressure is regulated only in the primary space 3 with the aid of the vacuum pump 21. The pressure in the secondary space 6 adapts passively through the connection device 35, as a function of changes in the primary space 3, so that the integrity of the secondary membrane 5 is not jeopardized. The connection device 35 may be fixed to remain in the vessel wall. FIG. 14 represents a partial view of the tank wall equipped with a T-connection circuit 37 establishing a fluid connection between the vacuum pump 21 and each of the primary 3 and secondary 6 spaces. A calibrated pressure loss device 38 or regulated is disposed on each branch of the connection circuit 37, so as to be able to generate a pressure differential on either side of the secondary membrane 5, without this differential exceeding a predetermined safety threshold, for example 3kPa . At least one isolation valve is provided to prohibit communication between primary space 3 and secondary space 6 outside the reheating procedure. The pressure drop devices 38 may be isolation valves. It is desirable to obtain a correct efficiency of the depression of the primary space 3 that the pressure losses between different areas of the primary space 3 are not too high. In particular, if the primary space 6 is filled with solid modular elements 7, it is advantageous for these solid modular elements 7 interposed between the membranes to incorporate flow channels in order to facilitate the flow of gases. Pressure regulation of the primary space 3 is facilitated. Such flow channels are made in such a way that they do not penalize the support function of the solid modular elements 7. FIGS. 15 and 16 thus illustrate an exemplary embodiment of the solid modular element in the form of a parallelepipedal spacer 47 having flow channels 48 and 49 in the form of perpendicular grooves on the side of the secondary diaphragm 5. FIG. 15 is a plan view from below of the parallelepipedal spacer 47. Figure 16 is a partial cross-sectional view of the vessel wall equipped with the part 47. In this example, the membranes 5 and 9 are corrugated. The technique described above for heating a tank can be used in different types of tanks, for example in an LNG tank in a land installation or in a floating structure such as a LNG tank or the like. Referring to Figure 17, a cutaway view of a LNG tanker 70 shows a sealed and insulated tank 71 of generally prismatic shape mounted in the double hull 72 of the ship. The wall of the tank 71 comprises a primary sealed barrier intended to be in contact with the LNG contained in the tank, a secondary sealed barrier arranged between the primary waterproof barrier and the double hull 72 of the ship, and one or two insulating barriers arranged respectively between the secondary watertight barrier and the double shell 72 and possibly between the primary watertight barrier and the secondary watertight barrier. In a manner known per se, loading / unloading lines 73 arranged on the upper deck of the ship can be connected, by means of appropriate connectors, to a marine or port terminal to transfer a cargo of LNG from or to the tank 71.

FIG. 17 shows an example of a marine terminal comprising a loading and unloading station 75, an underwater pipe 76 and an onshore installation 77. The loading and unloading station 75 is a fixed off-shore installation comprising a movable arm 74 and a tower 78 which supports the movable arm 74. The movable arm 74 carries a bundle of insulated flexible pipes 79 20 which can be connected to the loading / unloading pipes 73. The movable arm 74 can be adapted to all the jigs. LNG carriers. A connection pipe (not shown) extends inside the tower 78. The loading and unloading station 75 enables the loading and unloading of the LNG tank 70 from or to the shore facility 77. liquefied gas storage tanks 80 and connecting lines 81 connected by the underwater line 76 to the loading or unloading station 75. The underwater line 76 allows the transfer of the liquefied gas between the loading or unloading station. and unloading 75 and the on-shore installation 77 over a large distance, for example 5 km, which makes it possible to keep the tanker vessel 70 at a great distance from the coast 30 during the loading and unloading operations. In order to generate the pressure necessary for the transfer of the liquefied gas, pumps on board the ship 70 and / or pumps equipping the shore installation 77 and / or pumps equipping the loading and unloading station 75 are used. Although the invention has been described in connection with several particular embodiments, it is quite obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if those are within the scope of the invention. The use of the verb "to include", "to understand" or "to include" and its conjugated forms does not exclude the presence of other elements or steps other than those set out in a claim. The use of the indefinite article "a" or "one" for an element or a step does not exclude, unless otherwise stated, the presence of a plurality of such elements or steps. In the claims, any reference sign in parentheses can not be interpreted as a limitation of the claim.

Claims (24)

REVENDICATIONS1. A method of fluid management in a sealed and thermally insulating vessel (1) containing a low temperature liquefied gas (8), wherein a wall of the vessel has a multilayer structure having an outer carrier wall (2), a diaphragm primary seal (9) intended to be in contact with the liquefied gas contained in the tank, an intermediate space (3) situated between the primary waterproofing membrane and the outer supporting wall, the method comprising: sucking (13, 56) a gas phase of the intermediate space to the outside of the wall of the tank to lower the pressure in the intermediate space below a service pressure of the intermediate space, detecting (14, 57) a stabilization of the pressure in the intermediate space during the suction step, heating (15, 33) the wall of the tank, the step of heating the wall of the tank 15 comprising the step of emptying the tank of its cargo gas liquefied at low temperature. 2. The method of claim 1, wherein the suction of the gas phase is effected by means of a vacuum pump (21) regulated to achieve a target pressure. 20 The method of claim 2, wherein the difference between the predetermined target pressure and the service pressure of the interspace is greater than 10 kPa. 4. Method according to one of claims 1 to 3, wherein the stabilization of the pressure in the intermediate space is detected after the pressure has ceased to evolve for a stability period greater than 1 hour, preferably greater than 2h. 5. Method according to one of claims 1 to 4, further comprising the step of selecting (26) a reheating procedure as a function of the stabilized pressure in the intermediate space during the suction step. 30 The method of claim 5, wherein a fast reheat procedure (15) is selected when the stabilized pressure in the intermediate space during the suction step is less than or equal to a predetermined threshold pressure less than operating pressure. The method of claim 6, wherein the rapid reheat procedure (15) further comprises the step of injecting hot gas into the empty tank of its liquefied gas cargo at a low temperature. 8. Method according to one of claims 5 to 7, wherein a slow reheating procedure (33) is selected when the stabilized pressure in the intermediate space during the suction step is above a threshold pressure. predetermined lower than the operating pressure. The method of claim 8, wherein the slow reheat procedure (33) comprises the step of spraying a flow of liquefied gas at low temperature into the vessel (1) while the vessel is emptied of its liquefied gas cargo. at low temperature. 10. A method according to any one of claims 1 to 9, further comprising: detecting (27, 63) the presence of a liquid phase in the intermediate space, maintaining (13, 56) the aspiration of the gas phase in the intermediate space to substantially evaporate and / or desorb the entire liquid phase before heating the vessel wall. The method of claim 10, wherein the presence of a liquid phase is detected (27) in response to a stabilization of the pressure in the intermediate space at an intermediate level (Pi) between a predetermined target pressure and the pressure in service, and the evaporation and / or desorption of the entire liquid phase is detected in response to a subsequent decrease of the pressure in the intermediate space below the intermediate level. The method of claim 10, further comprising: measuring (54,58) the temperature in the interspace for a period of time from the lowering (52,56) of the absolute pressure in the interspace. detecting (68) a liquid phase in response to temperature stabilization in the interspace near the liquid-vapor equilibrium point of the liquefied gas for a predetermined target pressure, and detecting (65) evaporation and / or desorption of the entire liquid phase in response to stabilization of the temperature in the intermediate space in the vicinity of the temperature of the liquefied gas contained in the vessel. The method of any one of claims 1 to 9, wherein lowering the pressure in the interspace comprises: lowering (52) the pressure in the interspace to a first lower pressure threshold at the operating pressure, measuring (54) a first temperature (Tr) in the intermediate space after the pressure drop to the first pressure threshold, lowering (56) the pressure in the intermediate space to a second threshold of pressure lower than the first pressure threshold, measuring (58) a second temperature (Tm) in the intermediate space at successive times after the pressure drop to the second pressure threshold, determining (63) a difference between the second temperature and the first temperature, 15 maintain the suction and delay the reheating of the tank as the difference between the second temperature and the first temperature is not less than a temperature threshold In the predetermined manner, select the reheat procedure after the difference between the first temperature and the second temperature has fallen below the predetermined temperature threshold. 14. Method according to one of claims 1 to 13, wherein the intermediate space comprises a secondary sealing membrane (5) disposed between the outer bearing wall (2) and the primary sealing membrane (9), a secondary space (3) located between the secondary sealing membrane and the outer supporting wall, a primary space (6) located between the secondary sealing membrane and the primary sealing membrane, and a solid secondary insulating barrier (4); ) disposed in the secondary space, wherein a thickness of the primary space is much less than a thickness of the secondary space, in which the pressure is lowered in the secondary space and in the primary space so that the pressure difference between the secondary space and the primary space remains below a safety threshold, and in which the stabilization of the pressure is detected (14, 57) at least in the primary space for select the reheat procedure according to the stabilized pressure in the primary space. The method of claim 14, wherein the pressure in the secondary space is lowered below the pressure in the primary space. 5 16. Fluid management device for a sealed and thermally insulating tank (1) for containing a low temperature liquefied gas, in which a wall of the vessel has a multilayer structure comprising an outer supporting wall (2), a membrane of primary seal (9) intended to be in contact with the liquefied gas contained in the tank, an intermediate space (3) located between the primary waterproofing membrane and the outer supporting wall, the fluid management device comprising: Probes% n (41) for measuring the pressure in the intermediate space, a vacuum pump (21) connected to the intermediate space for sucking a gaseous phase from the intermediate space to the outside of the wall. the tank and able to lower the pressure in the intermediate space below a service pressure of the intermediate space, a control module (50) able to detect a stabilization of the in the intermediate space during the suction step and to select a reheating procedure according to the stabilized pressure in the intermediate space during the suction step. Apparatus according to claim 16, further comprising temperature sensors (45) for measuring the temperature in the intermediate space, wherein the control module controls the vacuum pump and the temperature sensors so as to: lower (52) the pressure in the intermediate space to a first pressure threshold lower than the operating pressure, measuring (54) a first temperature in the intermediate space after the pressure drop to the first pressure threshold lowering (56) the pressure in the intermediate space to a second pressure threshold lower than the first pressure threshold, measuring (58) a second temperature in the intermediate space at successive times after the pressure drop to at the second pressure threshold, 3032776 32 determine (63) a difference between the second temperature and the first temperature, maintain the suction and delay the reheating of the tank both that the difference between the second temperature and the first temperature is not less than a predetermined temperature threshold, selecting the rapid reheat procedure after the difference between the first temperature and the second temperature has become below the threshold of predetermined temperature. 18. Device according to claim 16 or 17, wherein the intermediate space comprises a secondary sealing membrane (5) disposed between the outer supporting wall and the primary sealing membrane, a secondary space situated between the membrane of secondary seal and the outer bearing wall, a primary space located between the secondary sealing membrane and the primary sealing membrane, and a solid secondary insulating barrier disposed in the secondary space, in which a thickness of the primary space is much smaller than a thickness of the secondary space, in which the vacuum pump (21) is connected at least to the primary space (3), the control module (50) being able to detect the pressure stabilization at least in the primary space to select the reheating procedure as a function of the stabilized pressure in the primary space. 19. Device according to claim 18, further comprising a fluid connection (35) connecting the secondary space to the primary space, the fluid connection comprising a valve (36) closed by default and able to open in response. 25 at a pressure differential greater than a predetermined opening threshold between the secondary space and the primary space. 20. Device according to claim 18 or 19, comprising a first vacuum pump (21) connected to the primary space and a second vacuum pump (22) connected to the secondary space. 30 21. Device according to claim 18 or 19, comprising a vacuum pump (21) connected parallel to the primary space by a first suction pipe and to the secondary space by a second suction pipe, each pipe of suction being provided with a pressure loss member (38). 3032776 33 22. Ship (70) having a double hull, a sealed and thermally insulating vessel (1) for containing a low temperature liquefied gas disposed in the double hull and a fluid handling device according to any one of claims 16 to 21 equipping the tank. 5 23. A method of loading or unloading a ship (70) according to claim 22, wherein a fluid is conveyed through insulated ducts (73, 79, 76, 81) to or from a floating or land storage facility ( 77) to or from a vessel of the vessel (71). 24. A transfer system for a fluid, the system comprising a vessel (70) according to claim 22, insulated pipes (73, 79, 76, 81) arranged to connect the tank (71) installed in the hull of the vessel. ship to a floating or land storage facility (77) and a pump for drawing fluid through the insulated pipelines from or to the floating or land storage facility to or from the vessel vessel. 15