EP3433530B1 - Facility for feeding fuel gas to a member consuming gas and for liquefying said fuel gas - Google Patents

Description

Technical area

The invention relates to the field of installations for processing a combustible gas, for example liquefied natural gas (LNG).

The invention relates more particularly to an installation aimed, on the one hand, at supplying combustible gas to a gas consuming member and, on the other hand, at liquefying said combustible gas.

Technological background

Liquefied natural gas is stored in sealed and thermally insulating tanks, in a two-phase liquid / vapor equilibrium state, at cryogenic temperatures. The thermal insulation barriers of liquefied natural gas storage tanks are the seat of a thermal flux tending to heat the contents of the tanks, which results in evaporation of the liquefied natural gas. The gas resulting from natural evaporation is generally used to feed a gas consuming organ in order to develop it. Thus, on an LNG tanker for example, the evaporated gas is used to power the powertrain making it possible to propel the ship or the generator sets supplying the electricity necessary for the operation of the on-board equipment. However, if such a practice makes it possible to recover the gas resulting from natural evaporation in the tanks, it does not make it possible to reduce its quantity.

In addition, when the combustible gas consists of a gaseous mixture, the composition of the vapor phase resulting from natural evaporation is different from that of the liquid phase and moreover tends to vary over time. Indeed, the vapor phase resulting from natural evaporation naturally presents a composition richer in the most volatile components, such as nitrogen for liquefied natural gas, than the liquid phase. However, it follows from these variations in composition that the calorific value of the gas resulting from natural evaporation like that of the liquefied gas remaining in the tank is variable over time when natural evaporation prevails. However, the supply of a consumer organ with a combustible gas whose calorific capacity undergoes significant variations is likely to cause imperfect combustion of the gas as well as malfunctions and variable efficiency of the gas consuming member.

We know from US-A-2010170297 a device for re-liquefying the gas resulting from natural evaporation in an LNG tank. This device comprises a heat exchange unit arranged above the LNG tank to condense the gas resulting from natural evaporation by heat exchange with a secondary coolant such as liquid nitrogen. The installation intended to produce, cool and liquefy nitrogen consumes energy.

JP0960799 describes an LNG storage installation with an LNG vaporization circuit and a gas recondensation circuit from natural evaporation. The vaporization of LNG in the vaporization circuit is produced by the heat supplied by the heater 24.

The document KR20100021774 describes an apparatus for supplying combustible gas to a high pressure gas injection engine in a ship. This device comprises a liquefied gas supply line connecting a liquefied gas fuel tank to a high pressure gas injection engine, a re-liquefaction circulation line, a compression unit installed in the liquid supply line. liquefied gas, a vaporized gas liquefaction unit, a vaporized gas re-liquefaction unit and a controller. The controller regulates the adjustment pressure of the liquefied fuel tank and the quantity of liquefied gas supply according to the load variations acting on the high pressure gas injection engine.

summary

An idea underlying the invention is to propose an installation aiming at supplying combustible gas to a gas consuming member and at re-liquefying said combustible gas which does not have at least some of the drawbacks of the prior art. Certain aspects of the invention start from the idea of using the liquid phase of the combustible gas as a refrigerant in a heat exchanger to cool and condense the gas resulting from natural evaporation.

• une cuve étanche et thermiquement isolante comportant un espace intérieur destiné à être rempli de gaz combustible dans un état d'équilibre diphasique liquide-vapeur;
• un échangeur de chaleur disposé à une position plus haute que la cuve étanche et thermiquement isolante, l'échangeur de chaleur comprenant une voie de vaporisation et une voie de condensation séparées de manière étanche l'une de l'autre par des parois d'échange de chaleur permettant de transférer de la chaleur entre un fluide contenu dans la voie de condensation et un fluide contenu dans la voie de vaporisation, la voie de vaporisation et la voie de condensation comportant chacune une entrée et une sortie,
• l'entrée de la voie de condensation étant raccordée à la cuve étanche et thermiquement isolante par un circuit collecteur de vapeur comportant une admission débouchant dans une portion supérieure de l'espace intérieur de la cuve pour prélever un premier flux de gaz combustible en phase vapeur dans l'espace intérieur de la cuve, l'entrée de la voie de condensation est disposée plus haut que la sortie de la voie de condensation,

• la sortie de la voie de condensation étant raccordée à l'espace intérieur de la cuve pour transférer par gravité une fraction liquide du premier flux de gaz combustible dans l'espace intérieur de la cuve, la fraction liquide du premier flux de gaz combustible étant obtenue par condensation dans la voie de condensation,
• l'entrée de la voie de vaporisation étant raccordée à la cuve étanche et thermiquement isolante par un circuit d'entrée de liquide, le circuit d'entrée de liquide comportant une admission débouchant dans une portion inférieure de l'espace intérieur de la cuve pour prélever un deuxième flux de gaz combustible en phase liquide dans l'espace intérieur de la cuve et une pompe de circulation pour transférer le deuxième flux de gaz combustible en phase liquide dans la voie de vaporisation,
• la sortie de la voie de vaporisation étant raccordée à un organe consommateur de gaz pour transférer une fraction vapeur du deuxième flux de gaz combustible vers l'organe consommateur de gaz, la fraction vapeur du deuxième flux de gaz combustible étant obtenue par vaporisation dans la voie de vaporisation.

According to one embodiment, the invention provides an installation for supplying combustible gas to a gas consuming member and to liquefaction of said combustible gas, the installation comprising:

• a sealed and thermally insulating tank having an interior space intended to be filled with combustible gas in a two-phase liquid-vapor equilibrium state;
• a heat exchanger disposed at a higher position than the sealed and thermally insulating tank, the heat exchanger comprising a vaporization path and a condensation path separated in a sealed manner from one another by exchange walls heat making it possible to transfer heat between a fluid contained in the condensation path and a fluid contained in the vaporization path, the vaporization path and the condensation path each comprising an inlet and an outlet,
• the inlet of the condensation channel being connected to the sealed tank and thermally insulating by a vapor collector circuit comprising an inlet opening into an upper portion of the interior space of the tank to draw a first flow of combustible gas in vapor phase in the interior space of the tank, the inlet of the track is located higher than the outlet of the condensation channel,

• the outlet of the condensation channel being connected to the interior space of the tank to transfer by gravity a liquid fraction of the first flow of combustible gas into the interior space of the tank, the liquid fraction of the first flow of combustible gas being obtained by condensation in the condensation channel,
• the inlet of the vaporization path being connected to the sealed and thermally insulating tank by a liquid inlet circuit, the liquid inlet circuit comprising an inlet opening into a lower portion of the interior space of the tank for taking a second flow of combustible gas in liquid phase in the interior space of the tank and a circulation pump to transfer the second flow of combustible gas in liquid phase in the vaporization path,
• the outlet of the vaporization path being connected to a gas consuming member for transferring a vapor fraction of the second flow of combustible gas to the gas consuming member, the vapor fraction of the second flow of combustible gas being obtained by vaporization in the path vaporization.

According to embodiments, such an installation may include one or more of the following characteristics.

According to one embodiment, the outlet of the spraying path is arranged lower than the inlet of the spraying path. Thus, both the first flow of combustible gas in the condensation path and the second flow of combustible gas in the vaporization path realize a downward movement, which promotes the exploitation of gravity to maintain the circulation of these two flows. . Furthermore, this orientation of the flows makes it possible to carry out a co-current heat exchange between the liquid phase of the combustible gas used as refrigerant and the gas resulting from natural evaporation to promote an isothermal heat exchange by phase change. Preferably in this case, the vaporization path is configured to flow the second flow of combustible gas in the form of falling liquid films.

According to one embodiment, the vaporization path of the heat exchanger comprises a phase separation tank disposed at the bottom of the vaporization path, the phase separation tank having a bottom wall and a side wall extending upward from the bottom wall, the outlet of the spray path opening through the side wall of the phase separation tank at a position spaced above the bottom wall. With such a phase separation tank, it is easy to separate by gravity the vapor fraction from the second flow of combustible gas from the fraction that remains liquid.

According to one embodiment, a purge circuit opens out through the bottom wall of the phase separation tank in order to be able to evacuate a liquid phase from the phase separation tank by gravity. Thus, in the case where an unvaporized fraction of the second stream remains, for example composed of the least volatile chemical species of a mixture (heavy bodies), an evacuation of this liquid fraction is facilitated in order to avoid saturating or obstruct the spray path.

According to one embodiment, the vaporization path of the heat exchanger is placed in depression, that is to say at a pressure lower than the pressure prevailing in the vapor phase of the sealed and thermally insulating tank. It is thus possible to further force the vaporization of the combustible gas in the vaporization path, by the cumulative effect of the heat supply in the condensation path and of the vacuum in the vaporization path. In addition, since the vacuum moves the two-phase equilibrium temperature down in the vaporization path, it is thus possible to increase the heat flow transferred from the vapor phase in the condensation path to the gas located in the vaporization route.

Preferably in this case, the absolute pressure in the vaporization path is greater than 120 mbar absolute. It is indeed preferable for the pressure inside the vaporization path to be higher than the pressure corresponding to the triple point of the methane phase diagram so as to avoid solidification of the natural gas inside the vaporization path. . The pressure in the vaporization path can in particular be between 500 mbar absolute and 980 mbar absolute.

According to the invention, the installation further comprises a vacuum pump or vacuum pump connected to the vaporization path to place the vaporization path of the heat exchanger at a pressure lower than the pressure prevailing in the vapor phase of the waterproof and thermally insulating tank

According to embodiments, such a vacuum pump can be controlled as a function of a flow rate setpoint or a pressure setpoint. Such a flow or pressure setpoint can be predetermined or generated by the gas consuming member.

• l'installation comporte un capteur de mesure de débit apte à délivrer un signal représentatif du débit du flux de vapeur aspiré à travers l'admission et refoulé vers l'organe consommateur de gaz et un dispositif de commande apte à commander la pompe à vide en fonction du signal représentatif du débit du flux de vapeur et d'une consigne de débit générée par l'organe consommateur de gaz.
• l'installation comporte un capteur de pression apte à délivrer un signal représentatif de la pression régnant dans la voie de vaporisation et un dispositif de commande apte à commander la pompe à vide en fonction du signal représentatif de la pression et d'une consigne de pression.

According to corresponding embodiments, the installation can have one or more of the following characteristics:

• the installation includes a flow measurement sensor capable of delivering a signal representative of the flow rate of the vapor flow drawn through the inlet and discharged towards the gas consuming member and a control device capable of controlling the vacuum pump in function of the signal representative of the flow rate of the vapor flow and of a flow rate setpoint generated by the gas consuming member.
• the installation comprises a pressure sensor capable of delivering a signal representative of the pressure prevailing in the vaporization path and a control device capable of controlling the vacuum pump as a function of the signal representative of the pressure and of a pressure setpoint .

The connection between the outlet of the vaporization channel and the gas consuming member can be direct or indirect, depending on the requirements of the consuming member. According to one embodiment, the aforementioned vacuum pump is arranged between the outlet of the vaporization path and the gas consuming member. According to another embodiment, a compressor is arranged between the outlet of the vaporization path and the gas consuming member to supply a flow of gas in the vapor phase at a pressure higher than the storage pressure in the tank.

According to one embodiment, the heat exchanger comprises a sealed and thermally insulating envelope delimiting an interior space containing the condensation channel, the envelope being arranged above the sealed and thermally insulating tank and comprising a lower opening communicating with the interior space of the sealed and thermally insulating tank and constituting the outlet of the condensation channel.

Such a sealed and thermally insulating envelope can be produced in different ways, for example in one piece with a top wall of the tank or else in the form of an assembly attached to the top wall of the tank.

According to one embodiment, a top wall of the sealed and thermally insulating tank has an opening connected to the lower opening of the envelope, the envelope further comprising a fixing flange arranged around the lower opening of the envelope, the fixing flange being attached to the top wall of the sealed and thermally insulating tank around the opening of the top wall.

Preferably in this case, the heat exchanger further comprises a collecting pipe extending from the lower opening of the envelope to near a top wall of the envelope and having a lower end opening into the interior space of the tank and an upper end opening into the interior space of the casing, the collecting pipe delimiting within the interior space of the casing an interior space of the collecting pipe forming the vapor collector circuit and an outer space of the collecting pipe forming the condensation path of the heat exchanger.

Thanks to these characteristics, the heat exchanger and the vapor collecting circuit can be produced in a relatively space-saving integrated form and having a relatively reduced exchange surface with the external environment, which limits the heat flows liable to increase natural evaporation.

According to another embodiment, the installation comprises a plurality of sealed and thermally insulating tanks comprising an interior space intended to be filled with combustible gas in a liquid-vapor two-phase equilibrium state, said vapor collector circuit being a collector circuit common connecting the inlet of the condensation channel to each of said tanks to collect the gases from evaporation in each of the tanks. It is thus possible to operate the heat exchanger jointly for a set of tanks.

• une pluralité de tubes parallèles à la canalisation collectrice disposés dans l'espace extérieur de la canalisation collectrice autour de la canalisation collectrice, les tubes parallèles constituant lesdites parois d'échange de chaleur de l'échangeur de chaleur,
• un distributeur d'entrée disposé dans l'espace intérieur de l'enveloppe, le distributeur d'entrée s'étendant à la périphérie de la canalisation collectrice et présentant une paroi de fond à travers laquelle débouche une extrémité supérieure de chacun des tubes parallèles,
• un tube d'entrée constituant l'entrée de la voie de vaporisation et s'étendant à travers l'enveloppe entre l'extérieur de l'enveloppe et le distributeur d'entrée,
• un carter de sortie disposé dans l'espace extérieur de la canalisation collectrice autour de la canalisation collectrice plus bas que la chambre d'entrée et présentant une paroi de sommet à travers laquelle débouche une extrémité inférieure de chacun des tubes parallèles, et
• un tube de sortie constituant la sortie de la voie de vaporisation et s'étendant à travers l'enveloppe entre le carter de sortie et l'extérieur de l'enveloppe.

According to a corresponding embodiment, the heat exchanger comprises:

• a plurality of tubes parallel to the collecting pipe arranged in the external space of the collecting pipe around the collecting pipe, the parallel tubes constituting said heat exchange walls of the heat exchanger,
• an inlet distributor arranged in the interior space of the envelope, the inlet distributor extending at the periphery of the collecting pipe and having a bottom wall through which opens an upper end of each of the parallel tubes,
• an inlet tube constituting the inlet of the vaporization path and extending through the enclosure between the exterior of the enclosure and the inlet distributor,
• an outlet casing disposed in the external space of the collecting pipe around the collecting pipe lower than the inlet chamber and having a top wall through which opens a lower end of each of the parallel tubes, and
• an outlet tube constituting the outlet of the vaporization path and extending through the envelope between the outlet casing and the exterior of the envelope.

In order to maximize the efficiency of the heat exchanger, it is indeed desirable to make thermal contact between the vaporization path and the condensation path over the greatest possible height of the external envelope. Advantageously, the inlet distributor is disposed higher than the upper end of the collecting pipe. Thus the parallel tubes can extend over almost the same length as the collecting pipe.

According to one embodiment, the tubes parallel to the manifold have heat exchange fins arranged on the outer surface of the tubes parallel to the manifold.

• admettre un premier flux de gaz combustible en phase vapeur à l'entrée de la voie de condensation depuis la portion supérieure de l'espace intérieur de la cuve étanche et thermiquement isolante à travers le circuit collecteur de vapeur,
• transférer un deuxième flux de gaz combustible en phase liquide depuis la portion inférieure de l'espace intérieur de la cuve jusqu'à l'entrée de la voie de vaporisation à l'aide de la pompe de circulation,

• réaliser un échange de chaleur entre le premier flux de gaz combustible dans la voie de condensation et le deuxième flux de gaz combustible dans la voie de vaporisation, de manière à vaporiser au moins une fraction du deuxième flux de gaz combustible, initialement en phase liquide, dans la voie de vaporisation en condensant au moins une fraction du premier flux de gaz combustible, initialement en phase vapeur, dans la voie de condensation,
• transférer par gravité la fraction liquide du premier flux de gaz combustible depuis la sortie de la voie de condensation jusqu'à l'espace intérieur de la cuve, et
• transférer la fraction vapeur du deuxième flux de gaz combustible depuis la sortie de la voie de vaporisation vers l'organe consommateur de gaz.

According to one embodiment, the invention also provides a method for supplying combustible gas to a gas consuming member and for liquefying said combustible gas, using a said installation, comprising:

• admit a first flow of combustible gas in the vapor phase at the entry of the condensation channel from the upper portion of the interior space of the sealed and thermally insulating tank through the vapor collecting circuit,
• transfer a second flow of combustible gas in liquid phase from the portion lower of the interior space of the tank up to the entry of the vaporization path using the circulation pump,

• performing a heat exchange between the first flow of combustible gas in the condensation path and the second flow of combustible gas in the vaporization path, so as to vaporize at least a fraction of the second flow of combustible gas, initially in the liquid phase, in the vaporization path by condensing at least a fraction of the first flow of combustible gas, initially in the vapor phase, in the condensation path,
• gravity transfer the liquid fraction of the first flow of combustible gas from the outlet of the condensation channel to the interior of the tank, and
• transfer the vapor fraction of the second flow of combustible gas from the outlet of the vaporization path to the gas consuming member.

Thanks to the downward orientation of the condensation channel, the first flow of combustible gas cooled by the heat exchange can flow by natural convection, ie by gravity, towards the interior space of the tank, which favors the production of a suction in the vapor collector circuit, thus maintaining the first flow without additional mechanical work.

Preferably, this method is implemented so as to vaporize all or almost all of the second flow of combustible gas in the vaporization path. Thus, by producing the vapor phase by forced vaporization of a flow of liquid taken from the lower portion of the tank, the content of the most volatile compounds is substantially equal to that of the liquid phase of the gas stored in the tank. The concentration of the most volatile compounds in the vaporized gas flow is therefore limited and substantially constant over time.

In addition, thanks to such an installation, the vaporization of the liquefied gas can be carried out without the aid of an external heat source, as opposed to forced vaporization installations using a heat exchange with sea water, a intermediate liquid or combustion gases from the engine or specific burners.

The gas present in the upper portion of the interior space of the tank thus acts as a hot source for the flow to be vaporized. Also, the installation allows both to produce a flow of vapor and to cool and condense the vapor phase resulting from natural evaporation present in the gaseous sky of the tank, so as to limit natural evaporation.

According to one embodiment, the invention provides a ship comprising an aforementioned installation.

According to one embodiment, the invention also provides a method of loading or unloading such a ship, in which combustible gas is conveyed through insulated pipes from or to a floating or terrestrial storage installation towards or from the tank. waterproof and thermally insulating of the ship.

According to one embodiment, the invention also provides a transfer system for a combustible gas, the system comprising the abovementioned ship, isolated pipes arranged so as to connect the tank installed in the hull of the ship to a floating storage installation or terrestrial and a pump for driving a flow of combustible gas through the insulated pipes from or to the floating or terrestrial storage installation towards or from the watertight and thermally insulating vessel of the ship.

Brief description of the figures

• La figure 1 est une illustration schématique d'une installation d'alimentation en gaz combustible d'organes consommateurs de gaz et de liquéfaction dudit gaz combustible, utile à la compréhension de l'invention mais n'en faisant pas partie
• La figure 2 est une demi-vue en perspective et en coupe longitudinale d'un échangeur de chaleur utilisable dans installation de la figure 1.
• La figure 3 est une vue en coupe transversale de l'échangeur de chaleur de la figure 2 selon la ligne III-III.
• La figure 4 est une vue agrandie d'un tube d'échange de chaleur de l'échangeur de chaleur de la figure 2.
• La figure 5 est une vue analogue à la figure 1 montrant un mode de réalisation selon l'invention de l'installation d'alimentation en gaz combustible d'organes consommateurs de gaz et de liquéfaction dudit gaz combustible.
• La figure 6 est une représentation schématique écorchée d'une cuve de navire méthanier comportant une telle installation et d'un terminal de chargement/déchargement de cette cuve.

The invention will be better understood, and other objects, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely by way of illustration and without limitation. , with reference to the accompanying drawings.

• The figure 1 is a schematic illustration of an installation for supplying combustible gas to gas consuming organs and for liquefying said combustible gas, useful for understanding the invention but not forming part of it
• The figure 2 is a half view in perspective and in longitudinal section of a heat exchanger usable in installation of the figure 1 .
• The figure 3 is a cross-sectional view of the heat exchanger of the figure 2 along line III-III.
• The figure 4 is an enlarged view of a heat exchanger tube of the heat exchanger of the figure 2 .
• The figure 5 is a view analogous to the figure 1 showing an embodiment according to the invention of the installation for supplying combustible gas to organs consuming gas and for liquefying said combustible gas.
• The figure 6 is a cutaway schematic representation of an LNG tank vessel comprising such an installation and of a loading / unloading terminal of this tank.

Detailed description of embodiments

In the description and the claims, the term “combustible gas” is generic in nature and is intended equally to refer to a gas consisting of a single pure body or to a gas mixture consisting of a plurality of components.

On the figure 1 , an installation 1 aiming, on the one hand, at supplying combustible gas to one or more gas consuming members and, on the other hand, at liquefying combustible gas is illustrated. Such an installation 1 can be installed on land or on a floating structure. In the case of a floating structure, the installation 1 can be intended for a liquefaction or regasification barge, for a liquefied natural gas transport vessel, such as an LNG carrier, or more generally for any equipped vessel. of a gas consuming organ.

Installation 1 illustrated on the figure 1 comprises a steam outlet line 3 which can supply directly or indirectly different types of fuel gas consuming devices not shown, namely in particular a burner, an electric generator and / or an engine for the propulsion of a ship.

Such a burner is integrated into an energy production installation. The energy production installation may in particular include a steam production boiler. The steam can be used to power steam turbines for energy production and / or to power a ship's heating network.

Such an electric generator comprises for example a thermal engine with mixed diesel / natural gas supply, for example of DFDE technology for “Dual Fuel Diesel Electric” in English. Such an engine can burn a mixture of diesel and natural gas or use either of these two fuels. The natural gas supplying such a heat engine must have a pressure of the order of a few bars to a few tens of bars, for example of around 6 to 8 bars absolute. For this, one or more compressors 4 can be provided on the steam outlet line 3.

Such an engine for propelling the ship is, for example, a low-speed two-stroke dual-fuel engine of “ME-GI” technology, developed by the company MAN. Such an engine uses natural gas as fuel and a small amount of pilot fuel which is injected before the injection of natural gas so that it ignites. To supply such an engine, natural gas must first be compressed under a high pressure of between 150 and 400 bar absolute, and more particularly between 250 and 300 bar absolute. For this, one or more compressors 4 can be provided on the steam outlet line 3.

The installation 1 comprises a sealed and thermally insulating tank 2. According to one embodiment, the tank 2 is a membrane tank. By way of example, such membrane tanks are described in patent applications WO14057221 , FR2691520 and FR2877638 . Such membrane tanks are intended to store combustible gas at pressures substantially equal to atmospheric pressure or slightly higher. According to other alternative embodiments, the tank 2 can also be a self-supporting tank and can in particular have a parallelepiped, prismatic, spherical, cylindrical or multi-lobic shape. Certain types of tank 2 allow gas to be stored at pressures substantially higher than atmospheric pressure.

The tank 2 has an internal space 7 intended to be filled with combustible gas. The combustible gas can in particular be a liquefied natural gas (LNG), that is to say a gaseous mixture mainly comprising methane as well as one or more other hydrocarbons, such as ethane, propane, n-butane , i-butane, n-pentane i-pentane, neopentane, and nitrogen in small proportion. The combustible gas can also be ethane or a liquefied petroleum gas (LPG), that is to say a mixture of hydrocarbons resulting from the refining of petroleum comprising essentially propane and butane.

The combustible gas is stored in the internal space 7 of the tank 2 in a liquid-vapor two-phase equilibrium state. The gas is therefore present in the vapor phase, in the upper part 8 of the tank 2 and in the liquid phase in the lower part 9 of the tank 2. This stratification is obtained naturally due to the specific density of each phase. The location of the liquid-vapor interface naturally depends on the filling level of the tank 2. The equilibrium temperature of the liquefied natural gas corresponding to its two-phase liquid-vapor equilibrium state is approximately -162 ° C when it is stored at atmospheric pressure.

Above the top wall 5 of the tank 2, there is shown a heat exchanger 10 which jointly makes it possible to re-liquefy gas in the vapor phase originating from natural evaporation in the upper part 8 of the tank 2 while forcibly vaporizing gas in the liquid phase taken from the lower part 9 of the tank 2.

• un circuit collecteur de vapeur 13 qui débouche au niveau du sommet de l'espace intérieur 12, pour amener de la vapeur du gaz combustible en haut de l'espace intérieur 12,
• un circuit de retour de condensat 14 qui débouche en bas de l'espace intérieur 12, pour collecter par gravité le gaz combustible condensé dans l'espace intérieur 12 et le ramener vers l'intérieur de la cuve 2.

For this, the heat exchanger 10 has an external gas-tight casing 11, preferably thermally insulating to limit the heat flow entering from the environment, which is arranged above the top wall 5 of the tank 2, and whose interior space 12 is in communication with the upper part 8 of the tank 2 by at least two connections:

• a vapor collector circuit 13 which opens at the top of the interior space 12, for bringing fuel gas vapor to the top of the interior space 12,
• a condensate return circuit 14 which opens at the bottom of the interior space 12, for collecting by gravity the combustible gas condensed in the interior space 12 and bringing it towards the interior of the tank 2.

On the figure 1 , the vapor collector circuit 13 and the condensate return circuit 14 pass through the top wall 5 of the tank 2, but other arrangements are possible, in particular for the condensate return circuit 14, for example by crossing the wall lateral 6 in the upper portion 8 of the tank 2.

As sketched in figure 50, the steam collector circuit 13 may include several branches connected to several tanks to serve as a common collector connecting a set of tanks to the condensation path of the heat exchanger 10. Valves, not shown, can be provided on each branch to keep the possibility of isolating the tanks from each other in this case.

In the same way, the condensate return circuit 14 could be connected to several tanks.

To extract heat from the interior space 12, the heat exchanger 10 also has a vaporization circuit 15 which is arranged in the interior space 12, shown here in the form of a helical coil but the shape of which can vary to a large extent. The vaporization circuit 15 is supplied with combustible gas in liquid phase from the lower part 9 of the tank 2 by a circulation pump 16 and an inlet pipe 17 joining the inlet of the vaporization circuit 15 by passing through seals the outer envelope 11. By removing the latent heat from the combustible gas in the vapor phase located in the interior space 12, the gas in the liquid phase circulating in the vaporization circuit 15 is vaporized and the vapor phase thus formed flows towards the outlet line 3, which is connected to the outlet of the vaporization circuit 15 by sealingly passing through the external envelope 11. For this, the outlet of the vaporization circuit 15 is preferably located lower than the inlet of the vaporization circuit 15. Thus, both the flow of gas being vaporized in the vaporization circuit 15 and the flow of gas being condensed in the interior space 12 have a downward movement nt, one under the effect of the circulation pump, the other only under the effect of gravity and the difference in density between the liquid and vapor phases.

Since the liquid phase is much denser than the vapor phase, the consumption of vapor by condensation creates a permanent suction effect in the vapor collector circuit 13, as shown by the arrow 19. It is therefore generally not necessary to have a circulation pump in the steam collector circuit 13.

In order to further force the vaporization of the combustible gas in the liquid phase circulating in the vaporization circuit 15, it is possible to place the latter under vacuum. For this, as shown in the figure 5 , a vacuum pump 51 can be used, for example in place of the compressor 4. The vacuum pump 51 must be a cryogenic pump, that is to say a pump capable of withstanding cryogenic temperatures below -150 ° vs. It must also comply with ATEX regulations, that is to say designed to eliminate any risk of explosion. In addition, a pressure drop member, for example an expansion valve 45, is placed at the inlet of the vaporization circuit 15, preferably inside the external envelope 11.

The figure 1 shows in broken lines another possible arrangement of the vapor collecting circuit, in the form of a collecting pipe 113 concentrically disposed in the condensate return circuit 14 from the upper part 8 of the tank 2 to the top of the interior space 12. In this case the admission of gas in the vapor phase takes place from the interior of the collecting pipe 113, while the condensate return flows in the annular space around the collecting pipe 113 in the condensate return circuit 14. For the rest, the operation is identical.

Although the figure 1 illustrates a heat exchanger whose vaporization path is contained and bathed in the fluid of the condensation path, a reverse configuration is also possible, namely a condensation path contained and bathed in the fluid of the vaporization path. Other configurations are also possible, for example with a heat exchanger in which the two channels have substantially the same volume.

With reference to figures 2 to 4 , we will now describe another embodiment of the heat exchanger. Elements analogous or identical to those of the figure 1 carry the same reference figure increased by 100.

On the figure 2 , the outer casing 111 has the general shape of a cylindrical bottle with a vertical axis, turned upside down with the neck. More specifically, the main body delimiting the interior space 112 has a larger diameter than the condensate return tube 114.

The watertight and thermally insulating walls are here formed of two parallel layers of mutually spaced metal sheets, with a vacuum space between the two. Other forms of thermal insulation could be used.

The condensate return tube 114 has bellows for absorbing thermal contraction when the temperature of the outer casing 111 changes, especially when it is put into service. It is terminated at its lower end by a fixing flange 21 for fixing to the top wall of the tank 2.

The collecting pipe 213 is arranged concentrically in the condensate return tube 114 from the end of the condensate return tube 114 and enters the interior space 112 over a large part of its height. The upper end of the collecting pipe 213 is open and opens into the upper part of the interior space 112. To guarantee the holding mechanical of the collecting pipe 213 in this position, fixing members can be provided to link the collecting pipe 213 to the external envelope 111. For example, fixing lugs 22 are here provided at the upper end of the collecting pipe 213 and attached to the vaporization circuit 115, itself fixed to the external envelope 111.

• un distributeur d'entrée 23 de forme annulaire ou torique disposé au sommet de l'espace intérieur 112,
• un carter de sortie 24 également de forme annulaire ou torique disposé au bas de l'espace intérieur 112 autour de la canalisation collectrice 213, et
• un grand nombre de tubes à ailettes 25 s'étendant parallèlement à la canalisation collectrice 213, de préférence verticalement, entre le distributeur d'entrée 23 et le carter de sortie 24.

The vaporization circuit 115 will now be described in more detail. It essentially comprises:

• an annular or toroidal inlet distributor 23 disposed at the top of the interior space 112,
• an outlet casing 24 also of annular or toroidal shape disposed at the bottom of the interior space 112 around the collecting pipe 213, and
• a large number of finned tubes 25 extending parallel to the collecting pipe 213, preferably vertically, between the inlet distributor 23 and the outlet housing 24.

The finned tubes 25 each have an upper end 27 opening into the annular chamber 26 of the inlet distributor 23 through the bottom wall thereof and a lower end 28 opening into the annular chamber 29 of the outlet housing 24 to through the cover wall of it. They constitute the heat exchange walls of the heat exchanger 110, which make it possible to jointly carry out the vaporization of the liquid phase flowing downwards in the finned tubes 25 and the condensation of the gaseous phase flowing down in the interior space 112.

The finned tubes 25 are distributed throughout the interior space 112 all around the collecting pipe 213, as partially shown in the figure 3 , in order to maximize the exchange surface between the two flows and to homogenize the heat transfers.

The figure 4 shows two embodiments of the finned tubes 25. In the right view, the tube body 30 is surrounded by fins 31 in the form of discs extending transversely to the tube body 30 and distributed in a mutually spaced manner over the entire length of tube body 30.

In the left view, the tube body 30 is surrounded by fins 32 in the form of rectangular or polygonal blades extending parallel to the tube body 30 over the entire length of the tube body 30 and distributed in a mutually spaced manner all around of the tube body 30.

In a variant not shown, the fins are eliminated, which makes it possible to reduce the lateral size of each tube and therefore to increase the number of tubes, to also obtain a high exchange surface.

The annular chamber 26 of the inlet distributor 23 has here a square cross section and extends in line with the fin tubes 25, therefore at the periphery of the collecting pipe 213. Furthermore, a conical wall is arranged in the center of the distributor inlet 23, with its top facing the upper end of the collecting pipe 213 to close the center of the inlet distributor 23, and thus force the vapor phase to flow laterally towards the top of the fin tubes 25 in leaving the collecting pipe 213.

An inlet tube 117 extends laterally from the annular chamber 26 to the outside of the outer casing 111. Sealed welds or seals, not shown, are provided around the inlet tube 117 at the level of the crossing of the outer casing 111 to maintain the sealing thereof. The inlet tube 117 is connected to the circulation pump 16 by any suitable pipe, preferably provided with thermal insulation.

The outlet casing 24 has a hollow toroidal shape around and away from the collecting pipe 213. Its bottom wall 33 is concave in order to form a phase separation tank which makes it possible to collect by gravity the non-vaporized part of the flow of gas in liquid phase injected from the inlet tube 117. A purge pipe 34 opening at the bottom of the bottom wall 33 makes it possible to evacuate this liquid fraction, for example to reinject it into the tank 2. Furthermore, an outlet tube 103 extends laterally from the annular chamber 29 to the outside of the envelope 111. The outlet tube 103 opens into the annular chamber 29 above the concave bottom wall 33, in order to avoid collecting the liquid phase. In practice, the filling level of the bottom wall 33 must be kept relatively low to avoid an overflow of the liquid phase towards the outlet tube 103. Sealed welds or seals not shown are provided around the tube. exit 103 at the crossing of the outer casing 111 to maintain the seal thereof. The outlet tube 103 is connected to the fuel gas consuming members, directly or via other gas processing equipment, for example, compressor, heater, etc.

In operation, the fact that the vapor phase collected in the upper part 8 of the tank 2 is channeled at the top of the heat exchanger 110 by the collecting pipe 213, ensures on the one hand that the heat exchanger 110 works on substantially its entire height and on the other hand that a convection / pumping by condensation movement is ensured on the vapor phase. The latter, relatively hot compared to the liquid phase located in the lower part 9 of the tank 2, enters through the collecting pipe 213 and arrives at the top of the heat exchanger 110. It then comes into contact with the surfaces d heat exchange of the vaporization circuit, namely the tubes 25, cools, which creates a first suction effect by thermal contraction of the vapor, then changes state by yielding its latent heat of vaporization to form droplets which then descend by gravity to the concave bottom wall 35 of the outer casing 111, which creates a second suction effect. It is thus possible to do without active pumping members to cause the circulation of the vapor phase.

In the vaporization circuit 115, the architecture shown here with an inlet at the top and an outlet at the bottom uses a film falling technique. The operation to be obtained is that this film has lost all of the components which can vaporize during the time between its entering chamber 26 and arriving in chamber 29, subject to the low volatility bodies which it is likely to contain and which will then arrive in liquid phase on the bottom wall 33.

A valve 49 is preferably arranged on the purge pipe 34, to close the purge pipe 34 during normal operation of the installation and open the purge pipe 34 intermittently to evacuate the liquid fraction rich in heavy bodies. The evacuation of the liquid fraction can be brought about either by injection of gas under pressure into the inlet tube 117, or by gravity under the sole effect of the hydrostatic pressure of the accumulated heavy bodies. This purge operation can thus be done even when the installation is in operation.

Alternatively, a valve 149 is used on the purge pipe 34 instead of the valve 49, in order to be able to close the purge pipe 34 if necessary and open the purge pipe 34 intermittently or continuously to evacuate the liquid fraction rich in heavy bodies . The evacuation of the liquid fraction can be caused by gravity when the valve is in the open position, under the sole effect of the hydrostatic pressure of the accumulated heavy bodies. This purge operation can also be done when the installation is in operation.

Alternatively, a pump external to the tank, not shown, can be used to evacuate this remaining liquid fraction, intermittently or continuously. One of the advantages of this architecture is that the risk of saturation of the vaporization circuit 115 by the liquid phase is relatively limited: if the heat supplied by the vapor is insufficient to vaporize the liquid, the remaining liquid phase can be evacuated as it arrives without interrupting the spraying process. This would not be the case with a boiling vessel fed from below and in which a liquid heel is brought to the boil.

As in the figure 5 , it is possible to further force the vaporization of the combustible gas in the liquid phase arriving in the vaporization circuit 115 by placing the latter under vacuum. The purge device and its operation will be modified in this case.

When the vaporization circuit 115 is placed under vacuum, a second valve 52 is added to the purge pipe 34 upstream of the valve 149 in order to create a buffer volume 53 which can take the form of a pipe or a reservoir. The operation of valves 52 and 149 is alternative: we start by opening the second valve 52 to let the buffer space 53 fill with heavy bodies. Then close the second valve 52 before opening the valve 149 to empty the buffer volume by gravity before closing the valve 149. The opening of the valves 52 and 149 can be caused either by gas injection or by electric control as for solenoid valves.
The opening frequency of valves 52 and 149 is directly linked to the composition of the LNG, so the more the LNG contains a large fraction of heavy compounds the greater the opening frequency of the valves 52 and 149.

The architecture of the heat exchanger 110 makes it possible to carry out a heat exchange with parallel currents or co-currents. In theory, this form of heat exchange has less efficiency than counter-current heat exchange. In fact, in a bi-fluid heat exchanger, the two fluids enter the exchanger with a given temperature difference between the two fluids. If the heat exchange is done against the current, the outlet temperature of one of the fluids tends towards the inlet temperature of the other and vice versa. On the other hand, in a co-current exchanger, the two fluids tend towards a mixing temperature.

These considerations are not an obstacle to the proper functioning of the heat exchanger 110 which is used as an evapo-condenser. In fact, the share of sensible heat in the heat exchanges in question is a minority, and the majority of the heat transfer is carried out isothermally by phase change.

By way of illustration, if the vapor phase of the combustible gas returns to -100 ° C in the collecting pipe 213, the proportion of sensible heat to bring this vapor to -160 ° C is approximately 130 kJ / kg while the latent heat necessary to condense it is 510kJ / kg. Thus, the majority of the heat transfer is isothermal. It is the same for the liquid phase in the vaporization circuit 115.

With reference to the figure 6 , there is a cutaway view of an LNG tanker 70 equipped with a fuel gas supply installation for gas consuming bodies and liquefaction of said fuel gas as described above. The figure 6 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 waterproof barrier intended to be in contact with the LNG contained in the tank, a secondary waterproof barrier arranged between the primary waterproof barrier and the double hull 72 of the ship, and two insulating barriers arranged respectively between the primary waterproof barrier and the secondary waterproof barrier and between the secondary waterproof barrier and the double shell 72.

In a manner known per se, loading / unloading lines 73 arranged on the upper deck of the ship can be connected, using appropriate connectors, to a maritime or port terminal to transfer a cargo of LNG from or to the tank 71.

The figure 6 represents an example of a maritime terminal comprising a loading and unloading station 75, an underwater pipe 76 and a shore installation 77. The loading and unloading station 75 is a fixed offshore 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 which can be connected to the loading / unloading pipes 73. The movable arm 74 can be adjusted to suit all sizes of LNG carriers. A connection pipe, not shown, extends inside the tower 78. The loading and unloading station 75 allows the loading and unloading of the LNG carrier 70 from or to the onshore installation 77. This comprises liquefied gas storage tanks 80 and connecting pipes 81 connected by the subsea pipe 76 to the loading or unloading station 75. The subsea pipe 76 allows the transfer of the liquefied gas between the loading or unloading station 75 and the shore installation 77 over a long distance, for example 5 km, which makes it possible to keep the LNG carrier 70 at a great distance from the coast during the loading and unloading operations.

To generate the pressure necessary for the transfer of the liquefied gas, pumps on board the ship 70 and / or pumps fitted to the shore installation 77 and / or pumps fitted to 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 in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these fall within the scope of the invention as defined by the claims.

The use of the verb "to include", "to understand" or "to include" and of its conjugated forms does not exclude the presence of elements or other stages than those stated in a claim.

In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

Claims (17)

1. An installation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas, the installation (1) including:

   - a leaktight heat-insulating tank (2) including an inner space (7) intended to be filled with combustible gas in a liquid-vapor two-phase state of equilibrium;

   - a heat exchanger (10, 110) placed in a higher position than the leaktight heat-insulating tank, the heat exchanger comprising a first path (15, 115) and a condensation path (12, 112) separated from each other in a leaktight manner by heat-exchange walls allowing heat to be transferred between a fluid contained in the condensation path and a fluid contained in the first path, the first path and the condensation path each including an inlet and an outlet,

   - the inlet of the condensation path being connected to the leaktight and heat-insulating tank by a vapor-collecting circuit (13, 113, 213) including an admission emerging in an upper portion (8) of the inner space of the tank to withdraw a first stream (19) of vapor-phase combustible gas in the inner space of the tank; the inlet of the condensation path is placed higher than the outlet of the condensation path,

   - the outlet of the condensation path (14, 114) being connected to the inner space of the tank to transfer by gravity a liquid fraction of the first stream of combustible gas in the inner space of the tank, the liquid fraction of the first stream of combustible gas being obtained by condensation in the condensation path,

   - the inlet of the first path (15, 115) being connected to the leaktight heat-insulating tank by a liquid inlet circuit (17, 117), the liquid inlet circuit including an admission emerging in a lower portion (9) of the inner space of the tank to withdraw a second stream of liquid-phase combustible gas in the inner space of the tank and a circulation pump (16) to transfer the second stream of liquid-phase combustible gas into the first path,

   characterized in that the first path is a vaporization path, the installation further comprising a vacuum pump (51) connected to the vaporization path (15, 115) to place the vaporization path of the heat exchanger at a pressure below the pressure prevailing in the vapor phase of the leaktight heat-insulating tank,
   and in that the outlet of the vaporization path (3, 103) is connected to a gas-consuming member to transfer a vapor fraction of the second stream of combustible gas to the gas-consuming member, the vapor fraction of the second stream of combustible gas being obtained during functioning, by vaporization of the combustible gas in the vaporization path placed at a pressure below the pressure prevailing in the vapor phase of the leaktight heat-insulating tank.
2. The installation as claimed in claim 1, in which the vacuum pump (51) is arranged between the outlet of the vaporization path and the gas-consuming member.
3. The installation as claimed in claim 1, in which the outlet of the the vaporization path (15, 115) is placed lower than the inlet of the vaporization path.
4. The installation as claimed in claim 3, in which the vaporization path of the heat exchanger includes a phase separation tank (33) located at the bottom of the vaporization path, the phase separation tank including a base wall and a side wall extending upward from the base wall, the vaporization path outlet (103) emerging through the side wall of the phase separation tank at a position spaced above the base wall.
5. The installation as claimed in claim 4, also including a purge circuit (34) emerging through the base wall of the phase separation tank to be able to evacuate a liquid phase from the phase separation tank by gravity.
6. The installation as claimed in any one of claims 1 to 5, also including a compressor (4) arranged between the outlet of the vaporization path and the gas-consuming member.
7. The installation as claimed in any one of claims 1 to 6, in which the heat exchanger includes a leaktight heat-insulating envelope (11, 111) delimiting an inner space (12, 112) containing the condensation path, the envelope being arranged above the leaktight heat-insulating tank and including a lower aperture (14, 114) communicating with the inner space of the leaktight heat-insulating tank and constituting the outlet of the condensation path.
8. The installation as claimed in claim 7, in which a top wall (5) of the leaktight heat-insulating tank has an aperture connected to the lower aperture of the envelope, the envelope also including a fastening clip (21) arranged around the lower aperture of the envelope, the fastening clip being attached to the top wall of the leaktight heat-insulating tank around the aperture of the top wall.
9. The installation as claimed in claim 8, in which the heat exchanger also includes a collecting pipe (113, 213) extending from the lower aperture of the envelope to a position close to a top wall of the envelope (11, 111) and having a lower extremity emerging in the inner space of the tank and an upper extremity emerging in the inner space (12, 112) of the envelope, the collecting pipe delimiting within the inner space of the envelope an inner space of the collecting pipe forming the vapor-collecting circuit and an outer space of the collecting pipe forming the condensation path of the heat exchanger.
10. The installation as claimed in claim 9, in which the heat exchanger includes:

    a plurality of tubes (55) parallel to the collecting pipe arranged in the outer space of the collecting pipe around the collecting pipe, the parallel tubes constituting said heat-exchange walls of the heat exchanger,

    an inlet distributor (23) arranged in the inner space of the envelope, the inlet distributor extending to the periphery of the collecting pipe and having a base wall through which emerges an upper extremity of each of the parallel tubes,

    an inlet tube (117) constituting the inlet of the vaporization path and extending through the envelope between the exterior of the envelope and the inlet distributor,

    an outlet case (24) arranged in the outer space of the collecting pipe around the collecting pipe lower than the inlet chamber and having a top wall through which emerges a lower extremity of each of the parallel tubes, and

    an outlet tube (103) constituting the outlet of the vaporization path and extending through the envelope between the outlet case and the exterior of the envelope.
11. The installation as claimed in claim 10, in which the inlet distributor (23) is arranged higher than the upper extremity of the collecting pipe (213).
12. The installation as claimed in claim 11, in which the tubes (25) parallel to the collecting pipe have heat-exchange vanes (31, 32) arranged on the outer surface of the tubes parallel to the collecting pipe (213).
13. The installation as claimed in any one of claims 1 to 12, also including a plurality of leaktight heat-insulating tanks including an inner space intended to be filled with the combustible gas in a liquid-vapor two-phase state of equilibrium, said vapor-collecting circuit (13) being a common collecting circuit connecting the inlet of the condensation path to each of said tanks to collect the gases derived from evaporation in each of the tanks.
14. A process for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas by means of an installation as claimed in any one of claims 1 to 12, including:

    - introducing a first stream of vapor-phase combustible gas (19) into the inlet of the condensation path (12, 112) from the upper portion (8) of the inner space of the leaktight heat-insulating tank through the vapor-collecting circuit,

    characterized in that he method further comprises:

    - transferring a second stream of liquid-phase combustible gas from the lower portion of the inner space of the tank to the inlet of the vaporization path (15, 115) by means of the circulation pump (16),

    - placing the vaporization path of the heat exchanger at a pressure below the pressure prevailing in the vapor phase of the leaktight heat-insulating tank,

    - exchanging heat between the first stream of combustible gas in the condensation path and the second stream of combustible gas in the vaporization path, so as to vaporize at least a fraction of the second stream of combustible gas in the vaporization path placed at a pressure below the pressure prevailing in the vapor phase of the leaktight heat-insulating tank while condensing at least a fraction of the first stream of combustible gas in the condensation path,

    - transferring by gravity the liquid fraction of the first stream of combustible gas from the outlet of the condensation path (14, 114) to the inner space of the tank, and

    - transferring the vapor fraction of the second stream of combustible gas from the outlet of the vaporization path to the gas-consuming member.
15. A ship (70) including an installation (1) as claimed in any one of claims 1 to 12.
16. A process for loading or emptying a ship (70) as claimed in claim 15, in which combustible gas is conveyed through insulated pipelines (73, 79, 76, 81) from or to a floating or land-based storage installation (77) to or from the ship's leaktight heat-insulated tank (71).
17. A system for transferring a combustible gas, the system including a ship (70) as claimed in claim 15, insulated pipelines (73, 79, 76, 81) arranged so as to connect the tank (71) installed in the ship's hull to a floating or land-based storage installation (77), and a pump for entraining combustible gas through the insulated pipelines from or to the floating or land-based storage installation to or from the ship's leaktight heat-insulated tank (71).

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