WO2015132307A1

WO2015132307A1 - Forced diffusion treatment for an insulating part made from expanded synthetic foam

Info

Publication number: WO2015132307A1
Application number: PCT/EP2015/054532
Authority: WO
Inventors: Nicolas HAQUIN; Nicolas THENARD; Raphaël PRUNIER; Bruno Deletre
Original assignee: Gaztransport Et Technigaz
Priority date: 2014-03-04
Filing date: 2015-03-04
Publication date: 2015-09-11
Also published as: AU2015226237B2; RU2016134936A; JP6570536B2; AU2015226237A1; RU2672748C2; SG11201606700YA; FR3018278B1; KR102331504B1; MY175711A; CN106170378B; FR3018278A1; JP2017516030A; PH12016501610B1; KR20160128407A; RU2016134936A3; PH12016501610A1; CN106170378A

Abstract

A method of forced diffusion treatment for a thermally insulating part (40) made from expanded synthetic foam, comprising: during a discharge step, heating the insulating part to a discharge temperature higher than ambient temperature and simultaneously exposing the insulating part to a gaseous atmosphere having low partial pressures of dinitrogen, dioxygen, carbon dioxide and the gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of the dinitrogen, ending the discharge step when the cumulative partial pressures of the dinitrogen, dioxygen, carbon dioxide and gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of the dinitrogen in the insulating part is less than a predefined threshold.

Description

FORCE DIFFUSION PROCESSING OF A FOAM INSULATING PIECE

EXPANDED SYNTHETIC

Technical area

The invention relates to the field of the use of expanded synthetic foams for producing thermal insulation parts, and more particularly thermoplastic or thermosetting closed cell foams.

Technological background

The porous closed-cell materials consist of a solid matrix in which many gas bubbles of larger or smaller sizes are trapped. Various thermoplastic and thermosetting synthetic materials can be used as matrices, for example polyurethane (PU), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polystyrene (PS), polyetherimide, polyethylene (PE), polypropylene (PP), polyimide . This list is not exhaustive.

In the expansion synthesis methods, a foaming agent is used. Two large families of blowing agents can be used depending, in particular, on the method of synthesis of the matrix. Expansion agents resulting from a chemical reaction, known as chemical agents, and expansion agents resulting from the vaporization of a liquid under a rise in temperature or a decrease in pressure, called physical agents. Some synthetic foams may contain only physical agents, for example pentane foamed polypropylene foam, and others exclusively chemical agents, for example carbon dioxide (CO2) foamed PU foam, and still others may be used. Both types of blowing agents are used, for example expanded polyurethane foams with several agents including pentane and expansion gases 141b, 365 and 245fa. In all cases, the blowing agent is or gives rise to an expansion gas which develops and occupies the cells of the foam.

The expansion gases are generally selected according to their implementation properties and their prices but also according to their thermal conductivity. They are usually chosen to limit as much as possible thermal transfers by conduction in the gas phase of the insulating material on the one hand and to have low diffusion coefficients in the selected matrix.

Once the expanded foam piece has been manufactured, the cells thus contain an initial gas or gas mixture. During the lifetime of the foam considered, the latter is the seat of diffusion phenomena that gradually vary the composition of the gas phase in the cells of the foam, including the partial pressures of the expansion gases and environmental gas. Thus, the chemical species whose partial pressure is lower in the environment than in the foam tend to escape from the foam whereas that whose partial pressure is lower in the foam than in the environment tend to penetrate into the foam. diffusion foam.

Thus, under open storage conditions, the majority of blowing agents tend to leave the foam while nitrogen and oxygen in the air tend to diffuse inside the insulating material. Since the expansion gases generally have lower thermal conductivities than those of the ambient gases, the insulation quality of the foams considered therefore tends to degrade for a long time. These phenomena are called aging of the foam.

This point is illustrated in FIG. 1 which represents the evolution of the thermal conductivity at 20 ° C., expressed in W / mK on the ordinate axis, as a function of the time of exposure to the ambient atmosphere, expressed in days on the abscissa axis, for two pieces of CO ₂ expanded polyurethane foam with a density of 130kg / m ³ . Curve 1 and the diamonds refer to a piece 25 mm thick. Curve 2 and squares refer to a 50 mm thick piece.

summary

An idea underlying the invention is to prevent and / or remedy the phenomena of aging of the foam described above.

For this purpose, according to one embodiment, the invention provides a method for forced diffusion treatment of a thermally insulating piece made of expanded synthetic foam, comprising:

during an evacuation step, heat the insulating part to a temperature exceeding the ambient temperature and simultaneously exposing the insulating part to a gaseous atmosphere with low partial pressures at least for the dinitrogen, oxygen, carbon dioxide and gases having a diffusion coefficient in the expanded, expanded synthetic foam or equal to that of the dinitrogen,

terminate the evacuation step when a plurality of partial pressures of the dinitrogen, oxygen, carbon dioxide and gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of the dinitrogen in the insulating part is less than at a certain threshold.

In other words, during the evacuation step, the insulating part is exposed to a gaseous atmosphere with partial pressures for the dinitrogen, the oxygen, the carbon dioxide and the gases having a diffusion coefficient in the synthetic foam. foams greater than or equal to that of the dinitrogen which are lower than partial pressures of these bodies in the air at normal pressure.

In addition, the evacuation step is terminated when a combination of the partial pressures of the dinitrogen, oxygen, carbon dioxide and gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of in the insulating part is below a determined threshold, a physical property of the insulating part related to said cumulative partial pressures reaches a determined threshold or after a determined time.

In addition, the thermally insulating part is disposed in a sealed and thermally insulating tank wall and forms an insulating barrier of the tank wall. Also, during the evacuation step, all or part of the tank wall is heated.

Such an evacuation step makes it possible to evacuate gases which are unfavorable to the thermal properties of the foam, in particular dinitrogen, oxygen, carbon dioxide, helium, dihydrogen, argon and the like.

According to one embodiment, the invention also provides a method for forced diffusion treatment of a thermally insulating expanded thermosetting polyurethane foam part comprising at least 80% closed cells, said method comprising:

during an evacuation step, heat the insulating part to a temperature higher than the ambient temperature and simultaneously exposing the insulating part to a gaseous atmosphere having partial pressures for the dinitrogen, oxygen, carbon dioxide and gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of the dinitrogen which are less than their partial pressure in the air at normal pressure, complete the evacuation step when a combination of the partial pressures of the dinitrogen, the oxygen, the carbon dioxide and the gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of the dinitrogen in the insulating part is below a determined threshold or that a physical property of the insulating part related to said cumulative partial pressures reaches a determined threshold or after a predetermined time.

According to one embodiment, the invention also provides a sealed and thermally insulating vessel intended to contain a low temperature liquefied combustible gas, in which a wall of the vessel comprises a multilayer structure mounted on a carrier wall, the multilayer structure comprising a primary sealing membrane in contact with the liquefied fuel gas contained in the tank, a secondary sealing membrane disposed between the primary waterproofing membrane and the supporting wall, a primary heat-insulating barrier disposed between the primary waterproofing membrane and the secondary sealing membrane, and a secondary thermally insulating barrier disposed between the secondary sealing membrane and the supporting wall, and wherein one or each thermally insulating barrier comprises thermally insulating pieces of expanded synthetic foam.

According to one embodiment, the tank is equipped with a forced diffusion treatment device comprising:

a heating device adapted to heat the primary sealing membrane and / or the supporting wall and / or the thermally insulating barriers to raise the temperature of the thermally insulating parts, for example by circulating hot gas,

a pumping device connected to the or each thermally insulating barrier comprising the thermally insulating pieces made of expanded synthetic foam and capable of reducing the total pressure of a gaseous phase in the or each thermally insulating barrier below the normal pressure, preferably in below 10 mbar, and a control unit adapted to:

controlling the heater and the pumping device to simultaneously heat the thermally insulating pieces to a discharge temperature above room temperature and expose the thermally insulating pieces to the total pressure below the normal pressure during an evacuation step, and

Brief description of the figures

The invention will be better understood, and other objects, details, characteristics and advantages thereof will appear more clearly in the course of the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes. with reference to the accompanying drawings.

FIG. 1 is a graph of the evolution of the thermal conductivity of an expanded synthetic foam as a function of the time of exposure to the ambient atmosphere.

FIG. 2 is a graph similar to FIG. 1 showing the influence of the aging temperature of the expanded synthetic foam.

• Figure 3 is a schematic sectional view of a sealed and insulating tank in which methods according to the invention can be implemented.

FIG. 4 is a schematic side view of an insulating panel that can be used in the tank of FIG. 3.

• Figure 5 is a schematic cutaway representation of a vessel tank LNG and a loading / unloading terminal of this vessel.

Detailed description of embodiments In the description and the claims, the term "normal pressure" will be used as a synonym for atmospheric pressure.

Processes for treating an insulating part made of synthetic foam to prevent or remedy the phenomena of aging of the foam, or even to improve the quality of thermal insulation of the insulating part, will now be described.

For this, during the first step, the so-called evacuation step, the treatment process consists in heating the insulating part to a discharge temperature greater than ambient temperature and simultaneously exposing the insulating part to a gaseous atmosphere with low partial pressures. for dinitrogen and oxygen, ie less than their partial pressure in air at atmospheric pressure.

This step makes it possible to accelerate the diffusion of the gases present in the foam towards the ambient environment. The foam is placed under high temperature conditions so that the diffusion coefficients of the gases present in the matrix are increased. In addition, the foam is placed under reduced pressure, at least for the main gases constituting the air, in order to accelerate the diffusion of the gases present in the foam, at least nitrous oxide and oxygen, to the external gaseous atmosphere.

This process is applicable to many varieties of foamed synthetic foams and blowing agents. Preferably, the expanded synthetic foam comprises at least 80% closed cells. Matrix materials and blowing agents may be selected from the polymers and agents mentioned in the introduction. By way of example, the expanded synthetic foam is in particular a thermosetting polyurethane foam comprising at least 80% of closed cells.

The discharge temperature is chosen so as not to damage the expanded synthetic foam. For this purpose, a discharge temperature of less than 100 ° C. is preferably chosen.

A temperature up to 100 ° C may be acceptable for certain polymers such as polypropylene or polyethylene. For many synthetic polymers, the discharge temperature is preferably below 80 ° C. This threshold of 80 ° C. is for example preferred for a foam of polyurethane, PVC, or polystyrene, especially to avoid the sublimation of polystyrene. The choice of discharge temperature may also take into account the heat resistance of other materials that are assembled to the insulation part, depending on the characteristics of the intended application.

Any rise in temperature is likely to increase the diffusion coefficient of the gases. As a measure of efficiency, the discharge temperature preferably corresponds to a substantial rise in temperature. According to one embodiment, the discharge temperature is greater than 50 ° C, or even greater than 60 ° C.

The heating of the insulating part may be achieved by various heating means, for example by radiation, conduction, for example brought into contact with a hot solid, or conducto-convection, that is to say placed in contact with a fluid hot.

According to one embodiment, the gaseous atmosphere of the evacuation step also has a low partial pressure for an expansion gas used for the manufacture of the expanded synthetic foam. Thanks to these characteristics, it is also possible to reduce the concentration of the expansion gas during the evacuation step, in order to reduce the thermal conductivity of the expanded foam.

It is advantageous for the implementation of this evacuation step that the insulating foam is foamed with one or more expansion agents having a diffusion coefficient as high as possible.

According to one embodiment, the expansion gas used for the manufacture of the expanded synthetic foam consists essentially of carbon dioxide. For example rigid polyurethane foam can be expanded with CO ₂ . The coefficient of diffusion of CO ₂ is higher than that of other known expansions agents, in particular expansion gases 141b, 245fa, 365, or pentane. In addition, a C0 ₂ expanded foam has the double advantage of not using gas that is likely to contribute significantly to global warming or the hole in the ozone layer, and to present the highest production costs. weak on the other hand. Indeed, the expanded foam C0 ₂ is expanded by chemical reaction of the water. For illustration, Table 1 gives orders of magnitude of the diffusion coefficients measured at ambient temperature on various polyurethane foams with a density of 120 to 135 kg / m ³ .

Table 1: Order of magnitude of diffusion coefficients

Table 2 illustrates the evolution of diffusion coefficients as a function of temperature, and shows in particular the increase of the diffusion coefficient with temperature.

Table 2: Effective diffusion coefficient D _eff of different gases in a low density PIR foam

Several techniques can be employed during the evacuation step to create the partial pressure gradients that allow the desired chemical species to escape from the foam, including oxygen and nitrogen and carbon dioxide. A first technique consists in subjecting the insulating piece to a reduced total pressure. According to a corresponding embodiment, the gaseous atmosphere of the evacuation step has a total pressure lower than the normal pressure, preferably less than 10 mbar. With this reduced pressure, the external environment is depopulated gas species likely to diffuse massively in the foam. The establishment and maintenance of this reduced pressure can be performed with a vacuum pump or other suction device. The suction makes it possible to eliminate the gases released from the foam of the ambient medium as and when they leave. In this vacuum technique, the heating of the insulating part is advantageously carried out by direct conduction or radiation.

A second alternative technique of the first is to immerse the insulating part in an atmosphere consisting essentially of one or more gas diffusing very badly in the foam. According to a corresponding embodiment, the gaseous atmosphere of the evacuation step is a gaseous phase of gas with large molecules in forced convection, that is to say a gaseous phase of gas having a molar mass greater than or equal to at 70g / mol.

The gaseous phase of large molecule gases, inasmuch as it has extremely low levels of nitrogen and oxygen, also creates a partial pressure gradient which favors the migration of dinitrogen and oxygen to the outside of the insulating part. In addition, the convection movement makes it possible to eliminate the gases exiting the foam from the ambient environment as they emerge.

Such a sweep with a gas whose diffusion coefficient in the foam is very low can be implemented with very large molecule gases, for example cyclopentane (C ₅ H ₀ ), gas CF ₄ , gas R-23, gas R-508 B, R-134 gas (CH ₂ FCF ₃ ), gas 141 b, gas 245fa, gas 365 or any other gas with a molar mass greater than or equal to 70 g / mol.

The table below represents the molar mass of several gases, the gases below having a molar mass greater than or equal to 70 g / mol being able to be used as gaseous atmosphere in which the insulation part is immersed during the evacuation step. Gas considered Molar mass (g / mol)

N ₂ 28

o ₂ 32

co ₂ 44 cyclopentane (C ₅ H ₁₀₎ 70

CF ₄ 88

R-23 70

R-508 B 95

R-134 (CH ₂ FCF ₃ ) 102

141b 104

245 134

365,148

Indeed, it is observed that the smaller the molar mass of a gas, the faster the phenomenon of diffusion through the foam.

The evacuation step is terminated after the partial pressures of some of the gases initially present in the cells have reached a target value. The most important and disadvantageous gases for the conductivity of the foam are nitrogen and oxygen, as well as C0 ₂ possibly, for example if it has been used as an expansion agent. It is therefore appropriate to complete the evacuation step when a plurality of partial pressures of at least the dinitrogen and the oxygen in the insulating part is less than a determined threshold.

According to one embodiment, the determined threshold is less than or equal to 30 mbar for the accumulation of partial pressures of dinitrogen, oxygen, carbon dioxide and gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that dinitrogen. This threshold corresponds approximately to a foam containing 3% of air.

The detection of such a condition can be carried out by direct or indirect experimental measurement and / or by calculation, in particular by numerical modeling. According to an embodiment corresponding to a direct measurement, the measurement of the nitrogen and oxygen in the insulating part during the evacuation step is measured and the evacuation step is stopped when the concentrations of the nitrogen and oxygen measured in the insulating room exceed the desired thresholds.

According to an embodiment corresponding to an indirect measurement, one or more physical properties related to the concentration of the dinitrogen and oxygen in the insulating part, such as the thermal conductivity of the foam, are measured and the evacuation step is stopped. when the measured property reaches a value which has been determined elsewhere, experimentally or by modeling, that it corresponds to the desired concentration.

According to one embodiment, the evacuation step is stopped after a determined time, which has been determined by the calculation, in particular by numerical modeling, taking into account the thermodynamic conditions of the treatment and the physical properties of the foam and chemical species present.

This forced diffusion treatment method can be applied to any kind of expanded foam insulating part. This forced diffusion treatment method can be implemented either in a dedicated processing station, for example in an insulating parts manufacturing plant, or directly in the operating environment of the insulating part.

According to one embodiment, the insulating part comprises reliefs or holes of small size increasing the exchange surface of the insulating part with the gaseous atmosphere. Thanks to these characteristics, the piece of foam has a ratio volume / area of exchange important so as to promote the diffusion phenomena during the evacuation step. For this purpose, the piece of foam has, for example, grooves of thickness of the order of one millimeter or holes of small diameter, for example about 2 mm, judiciously distributed in order to facilitate the diffusion of the gases without risking the creation of zones. gas convection. These reliefs or holes may in particular be arranged in the width or length of a parallelepiped panel.

According to one embodiment, the insulating part is disposed in a sealed and thermally insulating tank wall and forms an insulating barrier of the tank wall. The insulating foam foam part may in particular be part of a prefabricated insulation panel installed in the thickness of the wall of the tank, for example in a LNG tanker. As an illustration, it will be noted that examples of such prefabricated panels are described in the publication FR-A-2781557.

According to a corresponding embodiment, the evacuation step comprises the step of heating all or part of the tank wall. In the case of a tank intended to contain a cold product, for example a tank of liquefied gas, this heating of the tank wall must be implemented while the tank is empty. Such heating can be achieved by many means, for example by radiative heating, conductive heating or conducto-convective heating. According to one embodiment, an inner surface and / or an outer surface of the vessel wall is exposed to a hot gaseous atmosphere.

According to a preferred embodiment, the method further comprises one or more diffusion inhibitory actions applied to the insulating part during an operation step subsequent to the evacuation step, the said or each inhibiting action being effective for curbing a diffusion. gas into the interior of the piece of expanded material. Thanks to these characteristics, after the evacuation step, it prevents or slows the entry or the entry of ambient gases into the foam during its subsequent operation.

Preferably, the diffusion inhibiting action (s) are actions that are substantially continuous in time, so as to prevent or slow down durably the penetration of air or other ambient gases by diffusion in the synthetic foam. For this, different inhibitory actions can be used alternatively or in combination. Several inhibitory actions can be used in combination by being used simultaneously in time or being used successively in time during successive periods of the step of operating the insulating part.

Three embodiments of the inhibitory actions are presented below for illustrative purposes.

According to a first embodiment, the inhibitive action consists in exposing the insulating part to a gaseous atmosphere whose total pressure is kept below the normal pressure, preferably below 10 mbar. Thanks to these characteristics, the foam is maintained in a reduced pressure space. The ambient gas then having very low partial pressures, their tiny diffusion no longer affects the conductivity of the foam.

According to a second embodiment, the inhibiting action consists in keeping the insulating part at a temperature below 0 ° C., preferably below -20 ° C. Thanks to these characteristics, the foam is maintained under reduced temperature conditions at which the diffusion coefficients of the ambient gases in the matrix are much lower than they are during the evacuation step. As the diffusion phenomenon is therefore extremely slow, the migration of the ambient gas to the cells can be slowed down considerably to kinetics whose effect is negligible over the duration of use of the insulation.

Figure 2 illustrates the effect of low temperatures on the evolution of thermal conductivity over time. The thermal conductivity, expressed on the ordinate axis in W / mK, is plotted as a function of the aging time, expressed on the abscissa axis in days. The example relates to a PU foam at 40 kg / m ³ density. On curves 3 and 4, the thermal conductivity is measured at a positive temperature of + 20 ° C. In curves 5 and 6, the thermal conductivity is measured at a negative temperature of -120 ° C, which produces much lower values.

On the curves 3 and 5, the aging of the foam took place at a positive temperature of + 20 ° C. On curves 4 and 6, the aging of the foam took place at a negative temperature of -20 ° C. Thus, the effect of cold as a retarder of gaseous diffusion is very sensitive over a period of at least 60 days. The aging of a high-density foam produces similar observations starting from a higher initial thermal conductivity ranging from 0.024 W / mK for a foam whose expansion gases are HFCs and 141 b, to 0.027 W / mK for an expanded foam with C0 ₂ .

According to a third embodiment, the inhibitive action consists in exposing the insulating part to a gaseous atmosphere consisting essentially of a chemical species with large molecules that is weakly diffusive. Thanks to these characteristics, the foam is maintained in a non-diffusive gas environment.

Gases which have the following properties are preferably chosen: a diffusion coefficient in the matrix of the very low foam, a conductivity low thermal, and densities and viscosities greatly limiting thermal convection. Gases that can be used for this purpose include CF _4; the gas R-23, the gas R-508 B, the gas R-134 (CH ₂ FCF ₃ ), the gas 141b, the gas 245fa, the gas 365 or any other gas with a molar mass greater than or equal to 70 g / mol. The choice among the aforementioned gases may in particular be made according to the temperature and pressure conditions in the operating environment. It is appropriate that the gas chosen is in the vapor phase under the conditions of temperature and pressure of the operating environment. Also, to maintain these bodies in the vapor phase, it may be necessary to simultaneously maintain a relatively low pressure in the operating environment of the insulating part, for example in the primary or secondary insulating barrier of a gas tank wall. liquefied natural. As an illustration, gases that are particularly suitable for an operating environment in a primary or secondary insulating barrier of a tank wall of liquefied natural gas are, in particular, HFC R-508-B and HFC R-23 gases at a temperature of about -100 ° C to -120 and the CF ₄ at a lower temperature.

By way of illustration, the saturating vapor pressure of the HFC gas R23 is 60 mbar at -120 ° C. The saturated vapor pressure of the CF4 gas at -160 ° C is 30 mbar and 1.15 bar at -120 ° C.

Embodiments of the method applied to expanded foam blocks for use in the manufacture of a thermal insulation barrier arranged in the thickness of a liquefied gas tank wall will now be described.

According to an embodiment shown in FIG. 3, a sealed and thermally insulating tank 10 intended to contain a low temperature liquefied combustible gas has a prismatic shape and is integrated into a carrying structure constituted by the double hull of a ship. The outer wall and the inner wall of the double shell forming the supporting structure are designated by the numbers 1 1 and 12 in Figure 3. A ballast space 13 is defined between the two walls 11 and 12.

As shown schematically in FIG. 3, a wall of the tank comprises a multilayer structure mounted on the carrier wall 12. The multilayer structure comprises a primary sealing membrane 15 in contact with the liquefied fuel gas contained in the tank, a membrane of sealing secondary member 16 disposed between the primary sealing membrane 15 and the supporting wall 12, a primary heat-insulating barrier 17 disposed between the primary sealing membrane 15 and the secondary sealing membrane 16, and a secondary heat-insulating barrier 18 disposed between the secondary sealing membrane 16 and the supporting wall 12.

There are many materials that can be used in thermally insulating barriers. In the present embodiment, one or each of the thermally insulating barriers 17 and 18 comprises thermally insulating pieces of expanded synthetic foam.

In one embodiment, the constituent foam of the insulating blocks is treated once installed on board but in a phase preceding the cold setting of the vessels of the vessel. For this, the foam blocks are heated to an exhaust temperature at which the foam and any components associated with the foam, for example commonly used materials such as plywood, glass wool and triplex, are not damaged by heat. According to a preferred embodiment, this temperature varies from 60 to 80 ° C. Thus, the diffusion coefficients of the gases present in the foam are increased in order to reduce the duration of the forced diffusion treatment.

For this, it is possible to heat the inner space 20 of the tank and possibly the ballast spaces 13 to the desired temperature by means of a blower 21, blowing for example hot air or hot gases. exhaust recovered from a ship propulsion plant. Other heating means may also be employed. Figure 3 shows schematically a blowing pipe 22 opening into the inner space 20 and a blowing pipe 23 opening into the ballast space 13 for this purpose.

The or one of the insulation spaces 17 and 18 thus heated are also placed at reduced pressure, for example between 0.1 mbar and 10 mbar, in order to increase the motor pressure gradient of the diffusion of the gases present in the foam, that is to say, to ensure that the ambient environment of the foam has sufficiently low partial pressures for the gases leaving the foam to substantially empty the gas cells that they contain. For this, it is possible to use a vacuum pump 25 arranged to extract the gaseous phase of the primary thermally insulating barrier 17 and / or the heat barrier. secondary insulation 18. Figure 3 shows schematically a suction pipe 26 opening into the primary space and a suction pipe 27 opening into the secondary space for this purpose.

The diffusion of the gases is forced by the temperature and the concentration gradient until a satisfactory level is obtained. This evacuation step can be controlled automatically by an electronic control unit 30 controlling the vacuum pump 25 and the blower 21 using various feedback parameters 31, for example physical measurements taken in the tank by pressure sensors. , temperature, gas analysis or other.

This evacuation step is preferably followed by inhibitory diffusion actions to maintain the cells of the foam substantially free of gas penalizing the thermal conductivity.

One possibility of action is to maintain the gas isolation spaces at a reduced pressure throughout the operation of the vessel to reduce the partial pressures of species likely to migrate into the foam.

One possibility of action is to cool the vessel in such a way that the insulation foam is placed under reduced temperature conditions. The reduction of these temperatures makes it possible to greatly reduce the diffusion coefficients of the ambient gases in the foam, even if the isolation spaces 17 and 18 are replaced at atmospheric pressure. Each isolation space can thus be swept with steam nitrogen without risking to degrade the thermal conductivity properties of the foam as the vessels of the vessel are cold.

A possibility of action when the ship returns to near-ambient temperature conditions, that is to say when the tanks are emptied, is to perform a new vacuum draw with the vacuum pump 25, without necessarily heating simultaneously. the tank wall. This makes it possible to prevent the diffusion of the ambient gas into the foam and possibly to empty the peripheral layers of the foam of the flushing gas which could have diffused in reduced quantity.

Another possible action is to fill the isolation space with a gas having a diffusion coefficient in the matrix of the foam as low as possible. In order to improve the effect of the aforementioned inhibitive actions, it is also possible to apply a gastight or low gas diffusion coating on the outer surfaces of the foam exposed to the ambient gases. The establishment of such a facing is performed before the installation of foam blocks in the vessel wall, for example in a manufacturing facility where the forced diffusion treatment of the foam blocks has been previously performed. The cladding can then remain in place for the entire operating life of the insulating part.

According to one embodiment, illustrated in particular in Figure 4, the insulating part is a flattened parallelepipedal foam block 40 whose surface has two large faces 43, 44 parallel to the length and width directions of the block and mutually spaced in a thickness direction of the block, and peripheral faces 41, 42 smaller than the large faces and extending in the thickness direction of the block between the two large faces. The impervious coating 45 here has the shape of a band disposed longitudinally on the peripheral faces 41, 42 of the block all around the block and having a width less than the thickness of the block.

According to the embodiment of FIG. 4, this impervious coating is disposed only on the surfaces of the foam block 40 which are exposed to a temperature greater than -20 ° C. in use, that is to say portions close to the double shell 11, 12. For example, the width of the strip 45 is between 3 and 6 cm, and ideally 4.5 cm for a secondary insulation barrier of high density PU foam.

The gas-tight coating can be made in a number of ways. For example, the gas-tight coating comprises a layer of polymer resin and / or paint disposed on the outer surface of the insulating part and / or a metal sheet, for example at least a few microns thick, bonded to the outer surface of the insulating part. the insulating part. Such a metal sheet may be made of aluminum or other metals.

In the embodiment of Figure 4, the foam block 40 is used in a prefabricated insulation panel 50 whose structure is otherwise known, and which will now be recalled. The panel 50 has substantially the shape of a rectangular parallelepiped; it consists of a first plate 51 of plywood or a composite material 9 mm thick surmounted by the foam block 40, itself surmounted by a layer of tight composite material 52 intended to form the membrane secondary 16. On the impervious layer 52 is disposed a second block of foam 53 which itself bears a second plywood plate 54 of 12 mm thick. The subassembly 53, 54 is intended to constitute an element of the primary insulation barrier 17. It has, in plan, a rectangular shape whose sides are parallel to those of the subassembly 1, 40, 52. The two subsets have, seen in plan, the form of two rectangles having the same center. A peripheral rim 57, of constant width, exists all around the subassembly 53, 54 and is constituted by the edge of the subassembly 1, 40, 52. The impervious layer 52 is for example made in a multilayer composite composed of one or more metal foils and one or more fiberglass mats impregnated with polymeric resin.

The technique described above to prevent aging of the insulating parts 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 other.

A tank equipped with a forced diffusion treatment device as illustrated in FIG. 3 can also be made in the form of a terrestrial storage facility, for example for storing LNG, or to be installed in a floating structure, coastal or deep-sea, including a LNG tank, a floating storage and regasification unit (FSRU), a floating production and remote storage unit (FPSO) and others.

According to one embodiment, a vessel for the transport of a cold liquid product comprises a double hull and a aforementioned tank disposed in the double hull.

According to one embodiment, the invention also provides a method of loading or unloading such a vessel, in which a cold liquid product is conveyed through isolated pipes from or to a floating or land storage facility to or from the vessel vessel. According to one embodiment, the invention also provides a transfer system for a cold liquid product, 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 terrestrial and a pump for driving a flow of cold liquid product through the insulated pipelines from or to the floating or land storage facility to or from the vessel vessel.

Referring to Figure 5, a cutaway view of a LNG tank 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 two insulating barriers arranged respectively between the primary watertight barrier and the secondary watertight barrier and between the secondary watertight barrier and the double hull 72.

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. 5 represents 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 an arm mobile 74 and a tower 78 which supports the movable arm 74. The movable arm 74 carries a bundle of insulated flexible pipes 79 that can connect to the loading / unloading pipes 73. The movable arm 74 can be adapted to all gauges of 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 75 and the onshore installation 77 over a large distance, for example 5 km, which makes it possible to keep the tanker vessel 70 at great distance from the coast 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 obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they 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 "an" 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

A method of forced diffusion treatment of a thermally insulating piece (40) of expanded synthetic foam disposed in a sealed and thermally insulating vessel wall and forming an insulating barrier of the vessel wall, said method comprising:

during an evacuation step, heating all or part of the tank wall so as to heat the insulating part to a discharge temperature greater than ambient temperature and simultaneously expose the insulating part to a gaseous atmosphere having low partial pressures for dinitrogen, oxygen, carbon dioxide and gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of the dinitrogen, said low partial pressures being for each of these bodies less than the partial pressure to said body in i air at normal pressure,

terminate the evacuation step when a plurality of partial pressures of the dinitrogen, oxygen, carbon dioxide and gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of the dinitrogen in the insulating part is less than at a determined threshold, or that a physical property of the insulating part related to said accumulation of partial pressures reaches a determined threshold or after a determined time.

2. The method of claim 1, wherein the expanded synthetic foam comprises at least 80% closed cells.

3. The method of claim 1 or 2, wherein the foamed synthetic foam is a polyurethane foam.

The method of claim 3, wherein the polyurethane foam is a thermosetting foam.

5. Method according to one of claims 1 to 4, wherein the discharge temperature is less than 100 ° C, preferably less than 80 ° C.

6. Method according to one of claims 1 to 5, wherein the discharge temperature is greater than 50 ° C.

7. Method according to one of claims 1 to 6, wherein the expansion gas used for the manufacture of the expanded synthetic foam consists essentially of carbon dioxide.

8. Method according to one of claims 1 to 7, wherein the gaseous atmosphere of the evacuation step has a total pressure less than the normal pressure, preferably less than 10 mbar.

9. Method according to one of claims 1 to 8, wherein the gaseous atmosphere of the evacuation step is a gaseous phase of gas having a molar mass greater than or equal to 70 g / mol in forced convection.

10. Method according to one of claims 1 to 9, wherein the determined threshold is less than or equal to 30 mbar for the accumulation of partial pressures of dinitrogen, oxygen, carbon dioxide and gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of the dinitrogen.

11. Method according to one of claims 1 to 10, wherein the insulating part comprises reliefs or holes of small size increasing the exchange surface of the insulating part with the gaseous atmosphere.

12. Method according to one of claims 1 to 11, further comprising:

an inhibitory diffusion action applied to the insulating part during an operation step subsequent to the evacuation step, said inhibiting action being effective for braking gaseous diffusion towards the inside of the piece of expanded material.

13. The method of claim 12, wherein the inhibiting action comprises exposing the insulating part to a gaseous atmosphere whose total pressure is kept below the normal pressure, preferably less than 10 mbar.

14. The method of claim 12 or 13, wherein the inhibiting action comprises exposing the insulating part to a gaseous atmosphere consisting essentially of a chemical species having a molecular mass greater than or equal to 70 g / mol.

15. Method according to one of claims 12 to 14, wherein the inhibiting action consists in maintaining the insulating part at a temperature below 0 ° C, preferably below -20 ° C.

16. A method according to any one of claims 1 to 15, wherein the insulating member comprises a gas-tight coating (45) disposed on an outer surface of the insulating member.

The method of claim 16, wherein the gas-tight coating comprises a polymeric resin layer and / or a metal foil disposed on the outer surface of the insulating member.

18. The method of claim 16 or 17, wherein the insulating part is a flattened parallelepipedal foam block (40) whose surface has two large faces (43, 44) parallel to the length and width directions of the block and mutually spaced in a thickness direction of the block, and peripheral faces (41, 42) smaller than the large faces and extending in the thickness direction of the block between the two large faces, wherein the watertight coating presents form of a band (45) disposed iongitudinaiement on the peripheral faces (41, 42) of the block all around the block and having a width less than the thickness of the block.

19. A sealed and thermally insulating vessel (71) for containing a liquefied combustible gas at low temperature,

in which a wall of the tank comprises a multilayer structure mounted on a supporting wall (12), the multilayer structure comprising a primary sealing membrane (15) in contact with the liquefied combustible gas contained in the tank, a sealing membrane secondary (16) disposed between the primary sealing membrane and the supporting wall, a primary heat-insulating barrier (17) disposed between the primary waterproofing membrane and the secondary waterproofing membrane, and a secondary heat-insulating barrier (18) disposed between the secondary sealing membrane and the supporting wall, and wherein one or each thermally insulating barrier comprises thermally insulating pieces of expanded synthetic foam, characterized in that the tank is equipped with a forced diffusion treatment device comprising: a heater (21, 22, 23) adapted to heat the waterproofing membrane and / or the carrier wall and / or the thermally insulating barriers to raise the temperature of the thermally insulating parts,

a pumping device (25, 26, 27) connected to the or each thermally insulating barrier comprising the thermally insulating pieces of synthetic foam expanded and capable of reducing the total pressure of a gaseous phase in the or each thermally insulating barrier below normal pressure, preferably below 10 mbar,

and a control unit (30) adapted to:

terminate the evacuation step when a combination of the partial pressures of the dinitrogen, oxygen, carbon dioxide and gases having a diffusion coefficient in the expanded synthetic foam greater than or equal to that of the dinitrogen in the insulating pieces is less than at a certain threshold.