FR3066250B1 - DEVICE AND METHOD FOR COOLING LIQUEFIED GAS AND / OR NATURAL EVAPORATION GAS FROM LIQUEFIED GAS - Google Patents

Abstract

Device (10) for cooling natural evaporation gas for an installation (12) for producing energy, in particular on board a ship, characterized in that it comprises: - optionally, a main tank (14) for liquefied gas storage and having a first outlet (45) of natural evaporation gas, - means (170) for cooling liquefied gas, - a secondary tank (30) for cooled liquefied gas configured to store cooled liquefied gas by said cooling means; - a first heat exchange circuit (40) having an input for connection to said first output of said main tank for the circulation of natural evaporation gas in said circuit, said first circuit being configured to cooperate with said secondary reservoir so that said natural evaporation gas passing through said first circuit is cooled by cooled liquefied gas i stored in said secondary tank or from said secondary tank.

Description

Device and method for cooling liquefied gas and / or natural evaporation gas of liquefied gas

TECHNICAL FIELD The invention relates to a device and a method for cooling liquefied gas and / or natural evaporation gas of liquefied gas for an energy production installation, in particular onboard a ship, such as a ship of transport of liquefied gas or whose machines operate on liquefied gas.

STATE OF THE ART

In order to more easily transport gas, such as natural gas, over long distances, the gas is generally liquefied (to become liquefied natural gas - LNG) by cooling it to cryogenic temperatures, for example -163 ° C at atmospheric pressure. The liquefied gas is then loaded into specialized vessels.

In a liquefied gas transport vessel, for example of the LNG type, an energy production facility is provided to meet the energy requirements of the operation of the ship, in particular for the propulsion of the ship and / or the production of electricity for the vessels. equipment on board.

Such an installation commonly includes thermal machines consuming gas from an evaporator that is fed from the cargo of liquefied gas transported in the tank or tanks of the ship.

The document FR-A-2 837 783 provides for feeding such an evaporator and / or other systems necessary for propulsion by means of a submerged pump at the bottom of a tank of the ship.

In order to limit the evaporation of the liquefied gas, it is known to store it under pressure in the tank so as to move on the liquid-vapor equilibrium curve of the liquefied gas considered, thus increasing its vaporization temperature. The liquefied gas can thus be stored at higher temperatures which has the effect of limiting evaporation of the gas. The natural evaporation of gas is however inevitable, this phenomenon being called NBOG which is the acronym for English Natural Boil-Off Gas (as opposed to the forced evaporation of gas or FBOG, acronym for the English Forced Boil- Off Gas). The gas which naturally evaporates in the tank of a ship is generally used to supply the aforementioned installation. In the case (first case) where the quantity of naturally evaporated gas is insufficient for the fuel gas demand of the installation, the pump immersed in the tank is actuated to supply more fuel gas after forced evaporation. In the case (second case) where the quantity of evaporated gas is too great compared to the demand of the installation, the surplus gas is generally burned in a gas combustion unit, which represents a gas loss. combustible.

In the present art, the improvement of the reservoirs is such that the rates of natural evaporation (BOR - acronym Boil-Off Rate) of liquefied gases are becoming lower, whereas the machines of a ship are becoming more efficient. This has the consequence, in each of the first and second cases mentioned above, that the difference is very large between the amount of natural gas produced by evaporation and that required by the installation of a ship.

Consequently, there is an increasing interest for solutions for cooling the liquefied gas contained in a storage tank and managing the BOG generated in this tank, such as, for example, re-liquefaction or cooling units, such as those described in FIG. application WO-A1-2016 / 075399. The idea underlying this document is to propose a device for cooling a liquefied gas to limit the natural evaporation of the liquefied gas while maintaining it in a thermodynamic state for its storage in a sustainable manner. However, the heat exchanger technology described in this document is expensive and inefficient, and has other drawbacks which will be detailed in the following.

In addition, several parameters affect the generation of NBOG, such as fluid movements and ambient conditions. The energy requirements in a ship also vary a lot, depending on the operation performed or the speed of navigation. Therefore, it may be difficult to implement an effective BOG management solution because the amount of excess NBOG can vary enormously.

The present invention provides an improvement to the present technique, which is simple, effective and economical.

SUMMARY OF THE INVENTION

According to a first aspect, the invention proposes a device for cooling liquefied gas, in particular for an installation for producing energy on board a ship, characterized in that it comprises: optionally, a main storage tank of liquefied gas, - a first cooled liquefied gas separation tank, an inlet of which is connected to a first end of a first pipe whose second end is intended to be immersed in the liquefied gas contained in said main tank, preferably at the bottom of the tank, said first pipe being able to feed said first balloon with liquefied gas, means for depressurizing said first balloon with respect to said main tank, which are configured to apply in said first balloon a lower operating pressure to the pressure in said main tank, - vaporization means, equipping said first conduit and / or said inlet of said first balloon, so that at least a portion of the liquefied gas supplying said first balloon, said vaporized gas, is vaporized and at least one other part (for example: the rest) said liquefied gas, said cooled liquefied gas, is cooled to the saturation temperature at said operating pressure in said first flask, said first flask being configured to separate said vaporized gas and said cooled liquefied gas, and - supply means said main reservoir in said cooled liquefied gas contained in said first flask, for cooling the gas, liquefied and / or in the form of gas contained in said main tank. It is here the liquefied gas which is cooled, or rather more cooled compared to what it is already, and intended to be used to cool and control the temperature of the liquefied gas contained in the main tank.

The first balloon acts as a vacuum evaporator (ESV) and is associated with the first compressor which acts as a vacuum evaporation compressor. In known manner, the vaporization or depressurization of a gas causes a release of cooling energy. The vaporization means can therefore be likened to cooling means. Furthermore, vaporization means, depression means and depressurization means, have similar meanings or even identical in the sense of the invention. According to the invention, vaporization means equip the first pipe and / or the connection inlet of this first pipe to the first balloon. The first balloon can further form means of vaporization (complementary), as will be explained in the following. The invention thus proposes replacing the exchanger of the prior art with a vacuum evaporator, which makes it possible to obtain a larger cooling capacity and thus to improve the efficiency of the cooling of the gas, liquefied and / or in the form of of gas contained in the main tank.

The main reservoir is optional insofar as it can be considered as part or not of the device according to the invention. The device can for example be delivered without a main tank which is not part of the device. Alternatively, the device once mounted on a ship for example, is associated with a main tank which is part of the device according to the invention.

Advantageously, there is no heat exchanger (the drawback of which is to generate a cold loss by pinching) occurring during the expansion or vaporization step. In the prior art, with the use of such a heat exchanger, the entire light part is totally evaporated thanks in particular to the exchanger which evaporates the light part of the gas remained liquid after the depressurization. However, the depressurization and the exchanger are not sufficient to evaporate also heavy.

In the present application, the term heavy and light, respectively heavy gases or high molar masses and light gases or low molar masses. In one embodiment, the liquefied gas is liquefied natural gas. In this case, a light gas is methane. In liquefied natural gas, there may also be some nitrogen in the light part. The minor heavy part comprises, for example for liquefied gas propane, butane and ethane (which evaporates at a higher temperature or a lower pressure for example the operating pressure). In liquefied gas, heavy goods account for between 5.2% and 49.8% of the total liquefied gas mass. The heavies have for example molar masses between 25 and 500% greater than those of light).

The improvements made by this device are numerous and are for example the following: - a simpler architecture, a simpler control and a safer use through a cooling process that can take place entirely outside the main tank, - a better efficiency due to the suppression of pinching which can take place with a prior art exchanger, such as that described in the application W0-A1-2016 / 075399; given the operating pressures and the associated temperature drops, a nip of 1 to 2 ° C represents a cold power loss generated around 15%, - the cooling capacity is generated in the form of cooled liquefied gas which can be conveyed and used as needed, or stored for later use; this is particularly advantageous since this power can be generated by recovering the forced evaporation gas energy during the missing phases of NBOG corresponding to phases where hot power rather than cold power is needed, - a contrario, in considering the typical dimensions of a main tank, in particular of ship, the volume of gas stored in such a tank, and the sizes of the required cooling equipment as described in the aforementioned prior application, the cold power recovered with these equipment is not sufficient for its storage and its subsequent use, - the liquefied gas is intended to undergo a phase separation in the flask, only gas, which can be used in the installation, being intended to be sucked by the means of depression such as a compressor; no droplet can thus be sucked by the compressor, which could damage it; considering the operating pressure ranges, the liquefied gas temperatures and compositions, in most cases the liquefied gas will not be completely vaporized in a heat exchanger such as that described in the aforementioned prior application; for example, the liquid ratio in the initial architecture at 120mbara is between 0.12 and 32%, and at 800mbara (it is not possible to consider a pressure at 950mbara as proposed in the earlier application due to the pinch in the exchanger), it is between 0.8 and 92% (large variations due to different compositions of liquefied gas), - in the previous application, all the flow necessary for the supply of the installation is that is to say for the consumer, must pass through a compressor, which is not necessarily the case in the invention where only the amount of forced evaporation gas necessary is used to supplement the amount of gas produced. natural evaporation; thus, the capacity of the compressor is reduced, which reduces initial investment costs and operating costs; in addition, as each component of the device introduces losses, it is more effective overall to limit the flow rates flowing in the device; finally, the proposed device is easily connected to a conventional consumption installation of a ship, thus limiting the impact on the existing environment and giving more flexibility to the design of machines running on fuel gas of a ship; - The balloon is preferably located outside the main tank, facilitating and securing the device.

Overall, compared to the usual device installed on a ship where additional BOG is generated by supplying a heat exchanger to a liquefied gas by means of a pump, the device here reduces the total energy expended for the vaporization of the fuel. at 38%. The main goal is to generate cold by recovering the energy of vaporization which is typically an expense in a ship. Depending on the characteristics of the ship, including the speed profile, the efficiency of its machines, etc., the device can generate a cooling capacity up to 175% of the heat produced during a voyage of the ship (including return including commercial operation and waiting for entry of a channel).

The pressure in the main tank may vary depending on the depth in the tank due to the hydrostatic pressure.

In this application, the term "bottom" of tank or tank, a position located less than one meter from a bottom wall of the tank, the bottom wall being the wall of the tank closest to the center of the earth in operation. The pump or pumps are preferably as close to the bottom as possible to operate down to the lowest filling level possible (the distance from the bottom is limited by the fact that a pump too close to the bottom may have difficulty in initiate).

The device according to the invention may comprise one or more of the following characteristics, taken separately from each other or in combination with each other: said first balloon is a separation and / or expansion balloon; at least a part of said first balloon, and / or at least a part of said first pipe, and / or at least a part of said vaporization means, is / are housed or intended to be housed ( e) s in said main tank; said first flask is configured to be fed only with liquefied gas; the pressure of the liquefied gas in said first pipe is preferably greater than the hydrostatic pressure generated by the immersed portion of this first pipe in said main tank; the diameter of said first pipe, before said depressurizing means, is preferably as small as possible to limit the cooling of the liquefied gas in this pipe (limits the loss of cold); said first pipe is preferably configured so that the liquefied gas taken from said main tank remains liquid up to said depressurizing means; although the pressure drops in the first pipe because the hydrostatic pressure due to the immersion height in the main tank decreases, the pressure remains high enough that all the gas remains liquid; the pressure in the first pipe, at the inlet of the depressurizing means, is for example about 1 bar; the liquefied gas having only slightly warmed in the first pipe, it always remains at a temperature where it is liquid at about 1 bar (for example at about -160 ° C); said vaporization means comprise a valve, for example JT or Joule-Thomson and / or a portion of the first pipe, located in particular downstream of the valve; the vaporization of the liquefied gas taken preferably takes place (mainly or more than 80% or even 90%) just after the valve, in said portion of first pipe; the liquefied gas is also cooled in this portion of pipe because of the depression by "flash" evaporation effect (spontaneous depression); this portion of pipe may be of a larger diameter than the portion of first pipe located before the valve, in particular so as to have a sufficient flow) because the vaporized gas occupies more volume; alternatively, the vaporization can take place mainly or almost exclusively (more than 80%) in said first balloon, if the portion of pipe between the valve and the first balloon is reduced or zero; in this case, unless the first balloon is of sufficient volume, it may not have continuous operation; it would therefore be necessary to wait until the end of the phenomenon of evaporation and cooling of the liquefied gas takes place, at a temperature just below the boiling point at the new pressure, after depression ("flash") to empty the first balloon , especially in the secondary tank mentioned below; one could also in this case in particular replace the valve, for example JT, by a simple two-state valve (all or yours ie 100% closed / 100% open); said depressurizing means comprise at least a first compressor, an inlet of which is connected to a first gas outlet of said first flask, and an outlet of which is capable of supplying combustible gas, in particular to said installation, said first compressor being suitable sucking at least a portion of said vaporized gas into said first flask and applying said operating pressure to said first flask; alternatively or additionally, the vacuum means comprise at least one pump, an inlet of which is connected to a liquid outlet of said first balloon; in this variant, at least one compressor could be used to suck the vaporized gas contained in said first balloon; said supply means comprise a second pipe, a first end of which is connected to a second outlet of cooled liquefied gas of said first tank, and of which at least a second end intended to open into said main tank, said second pipe being able to inject at least a portion of said cooled liquefied gas from said first flask in said main tank; the connection of the first balloon to said main tank, by means of said second pipe, can be direct or indirect; that is, the second conduit may comprise or be associated with other fluid communication components or divided into sections between which such components are disposed; this may be the case of all the pipes mentioned in the context of the invention; gas, in liquid and / or gaseous form, can be injected into said main tank, in particular by means of said second pipe; a mixture of gas and steam can be injected into the main tank; if this mixture is reinjected at the bottom of the tank, the gaseous part of the mixture will tend to recondense under the effect of the hydrostatic pressure of the gas and the temperature of the liquefied natural gas in the main tank; this can lead to a slowing down of the pressure drop in the main tank; the device comprises a first pump connected to said second end of said first pipe, and intended to be immersed in said liquefied gas contained in said main tank, preferably at the bottom of the tank, so as to force the circulation of liquefied gas through said first driving to said first balloon; alternatively, the device is devoid of such a first pump; this is for example the case when the first balloon and the first pipe are in said first tank; the device comprises a second pump connected to said second pipe so as to force the circulation of at least a portion of said cooled liquefied gas through said second pipe from said first tank to said main tank; alternatively, this second pump would not be necessary, for example in the case of a batch operation where the first flask would be fed with liquefied gas to a predetermined filling level, it would then be depressurized to generate a cooling of liquefied gas and partial evaporation, which would cause a rise in pressure in said first flask to a value substantially close to the pressure in the main tank, sufficient to make the second pump optional; - The first pipe is equipped with an all-or-nothing valve, and able to be closed for example when a vacuum is created in said first balloon; the first or the second pump may be a fuel pump or a bilge pump equipping the vessel; this type of pump is typically capable of providing a maximum flow rate of the order of 25-30 t / h; alternatively, a pump of higher maximum flow rate can be used, in particular for the first pump, which would for example be able to provide a maximum flow rate of 300t / h, preferably see up to 2500t / h; the assembly formed by the first balloon, the first compressor and the first pump, acts as a vacuum evaporation means (or a vacuum evaporator - ESV); generally, in the present invention, the assembly formed by a balloon, a compressor and a pump, is assimilated to vacuum evaporation means; the vaporizing means are preferably configured to lower the pressure of the gas to the operating pressure of the first balloon; said second output of said first compressor is connected to an input of a second compressor, an output of which is capable of supplying fuel to said installation; said second pipe comprises or is connected to a plunger intended to be immersed in the liquefied gas contained in said main tank, and / or a spray boom in said main tank, for injection of cooled liquefied gas into said main tank ; the injection of cooled liquefied gas can therefore be carried out in the gas and / or in the liquefied gas contained in the main tank; said second outlet of said first flask is connected to a first inlet of a secondary tank, so as to supply this tank with cooled liquefied gas and to store cooled liquefied gas in said tank; the secondary reservoir is configured to contain said cooled liquefied gas at a pressure greater than said operating pressure in said first flask; the secondary tank is thus overpressurized with respect to the first balloon, and is for example at atmospheric pressure; the secondary tank can therefore be cheaper especially since it can be intended to store a large volume of gas; it is an advantage of this secondary reservoir; thus, the cooled gas could be accumulated in the first flask when the needs of the installation are greater than the natural evaporation, then be poured into the main tank so as to slow the natural evaporation when the needs of the installation are less than natural evaporation; the cooled liquefied gas contained in said secondary tank can be considered as subcooled liquefied gas; "Subcooled" means that the gas is at a temperature strictly below the boiling temperature (i.e., the saturation temperature) at the pressure to which the gas is subjected; in the secondary tank, the liquefied gas is at such a pressure that it can be considered as subcooled; the secondary reservoir acts as a fluid cooling heat exchanger, in particular BOG; said second pump is located between said second outlet of said first flask and said first inlet of said secondary reservoir; said secondary reservoir comprises a first outlet of at least a portion of said cooled liquefied gas connected to said second conduit, said second conduit being adapted to convey at least a portion of said cooled liquefied gas from said secondary reservoir to said main reservoir; said device comprises at least one heat exchange circuit configured to cool a fluid flowing in said circuit through at least a portion of the cooled liquefied gas stored in said secondary tank or from said secondary tank; this heat exchange circuit can be located in the secondary tank, be attached to or associated with the secondary tank, or be spaced from this secondary tank; a cooled liquefied gas pipe may for example be used to supply said heat exchange circuit, which may be part of a separate exchanger; alternatively, the cooled liquefied gas used to cool the fluid flowing in said heat exchange circuit, could come from another source, such as the main tank or the first balloon for example; the combination of said secondary reservoir and of said heat exchange circuit makes it possible to reprocess the natural evaporation, with a very good yield, since the pinch relative to the exchanger is small compared to the difference in temperature between the natural evaporation (the vapor phase gas at the inlet of the secondary reservoir at a temperature for example between -80 ° C and -160 ° C or more precisely between -100 and -140 ° C) andthe liquid gas, thanks in particular to the fact that the gas liquid is cooled; of course, one would have the same advantage with an exchange with the cooled gas of said first balloon or the main tank in the absence of secondary tank; in other words, cooled liquefied gas can be stored in the secondary tank, the first tank and / or the main tank; said heat exchange circuit comprises an inlet connected to a natural evaporation gas outlet of said main tank; in this context, said heat exchange circuit can make it possible to reprocess the natural evaporation of the main tank, with a very good efficiency, since the pinch relative to the exchanger would be small compared to the difference in temperature between the natural evaporation and the liquid gas, in particular because the liquid gas is cooled; said input of said circuit is connected to said output of at least one compressor, such as said first or second compressor, which is supplied with natural evaporation gas from said outlet of said main tank; the natural evaporation gas is thus compressed (which increases its temperature) before passing into the exchanger or the exchange circuit with the cooled liquid gas; said input of said circuit is connected to said output of at least one compressor, such as said first or second compressor, by a primary circuit of a first heat exchanger, said first heat exchanger comprising a secondary circuit of which an input is connected said natural evaporation gas outlet of said main reservoir, and an outlet of which is connected to said inlet of said first or second compressor; the natural evaporation gas taken from the main tank will be heated during its passage in said secondary circuit, which is not a problem since it must in any case be reheated if it is used to feed the tank. installation; advantageously, a prior exchange takes place (the exchange must be done beforehand since the natural evaporation gas is less cold than the cooled liquid gas) between the totality of the natural evaporation gas (including a part supplying the installation) and a compressed part of this natural evaporation gas (the surplus beyond the consumption of the installation which is recondensed); said heat exchange circuit includes an outlet connected to an inlet of a second tank, said second balloon having a first cooled liquefied gas outlet connected to said second line for injection of cooled liquefied gas into said main tank ; alternatively, the device could be configured to reinject into the main tank, for example at the bottom of the tank, a gaseous part of the mixture, which will tend to recondense under the effect of the hydrostatic pressure of the gas and the temperature of the gas liquefied in the main tank; said second balloon is a balloon and / or phase separation; said output of said circuit is connected to said input of said second balloon by a valve, such as a Joule-Thomson effect valve (whose acronym is JT), for the purpose of reducing the temperature of the gas by adiabatic expansion; the natural evaporation gas can thus be relaxed; the compression / depression, on either side of the exchanger or the heat exchange circuit, can make it possible to obtain a temperature of the natural evaporation gas that is lower, and thus to condense more evaporation gas natural; the device comprises a second heat exchanger of which a primary circuit has an input connected to an output of a third pump intended to be immersed in the liquefied gas of said main tank, and an output of said cooled liquefied gas, and a secondary circuit has a an input connected to said first conduit and an output connected to the input of said first balloon; said second heat exchanger is not immersed in the liquefied gas of said main tank, nor mounted in said main tank; the output of the primary circuit of said second heat exchanger is connected to an inlet of said secondary tank, for the purpose of supplying cooled liquefied gas from said secondary tank; the device is devoid of components other than pumps and / or pipes, immersed in the liquefied gas contained in said main tank; said liquefied gas comprises at least one so-called pure part comprising a gas or pure body and said cooled liquefied gas and said vaporized gas comprise said at least one pure part. In the case where the liquefied gas is liquefied natural gas, such a pure part may consist of methane.

In the present application, "pure" is understood to mean a single chemical body or species as opposed to a mixture of bodies or species. Said pure gas is for example a light gas or a heavy gas.

The present invention also relates to a vessel, in particular for transporting liquefied gas, comprising at least one device as described above.

The present invention also relates to a method for cooling liquefied gas for a power generation installation, in particular on board a ship, by means of a device as described above, characterized in that it comprises: a a liquefied gas sampling step contained in said main tank, said liquefied gas being taken from said first line at a sampling temperature, a step B of said withdrawn gas at a pressure of expansion less than a saturation vapor pressure of said a gas taken at said sampling temperature so that a part of said withdrawn gas vaporizes under the effect of the expansion, and that a remaining part of said sampled gas remains liquid and is cooled to a temperature below that of said sampling temperature, in particular the fact that said sampled gas is cooled to a saturation temperature at said expansion pressure, a step C of filling said first flask with liquefied gas and separating, in particular by gravity, into said flask of said vaporized gas with respect to said cooled liquid gas, a step D of supplying said installation with at least a portion of said vaporized gas contained in said first flask, and a step E of cooling the liquefied gas contained in said main tank by means of cooled liquefied gas contained in said first flask, for cooling the gas contained in said main tank.

Saturation vapor pressure is the pressure at which the gaseous phase of a substance is in equilibrium with its liquid or solid phase at a given temperature in a closed system.

According to the invention, instead of using the vacuum and the cooling in a vaporization chamber and the heat exchange between this vaporization chamber and the liquefied gas in a balloon, for cooling the liquefied gas poured into the main tank, a flash evaporation is used in the flask, the cooled liquid resultant of which is returned to the main tank. The advantage is mainly the suppression of the pinching of the heat exchange between the vaporization chamber and the liquefied gas of the balloon.

According to one embodiment, the liquefied gas sample consists of a pure gas, for example methane. In this case, the liquefied gas flowing in said first pipe may consist of a mixture comprising this pure gas, for example liquefied natural gas comprising methane.

The method according to the invention may comprise one or more of the following steps or characteristics, taken separately from each other or in combination with each other: step E comprises the injection of cooled liquefied gas into said main tank, by circulation in said second pipe, for cooling the liquefied gas contained in said main tank; the method comprises a step of spraying droplets of liquefied gas cooled in the gas contained in said main tank, this gas being located above the level of liquefied gas contained in the main tank, the method comprises an outgoing gas compression step said first output of said first balloon; the pressure in said first balloon is between 120 and 950mbara, and / or the pressure in said main tank is between 20 and 700mbarg, between 20 and 350mbarg, or between 20 and 250mbarg, particularly for an atmospheric tank, and is at a pressure of up to 10mbara for a pressure tank, and / or the expansion causes an evaporation fraction of between 0.94 and 15.18%, and / or the flow rate in the first pipe is between 18.09 and 374.7 / h, and / or the rate of production of liquefied gas cooled in said first flask is between 15.35 and 371.6t / h, and / or the secondary reservoir has an internal volume or capacity between 1312 and 86037m3, and / or the temperature of the cooled gas, after sampling of liquefied gas or natural evaporation gas, and cooling of this gas, is between -159 and -180.4 ° C, and / or the expansion degassing of compressed natural evaporation results in a fraction of evaporation between 81.63% and 100%; the method comprises a step of preheating liquefied gas taken from said main tank by heat exchange with the fluid flowing in said primary circuit, after the expansion and before the injection of said liquefied gas which may be partially or completely vaporized in said first balloon ; the method comprises a precooling step liquefied gas taken from said main reservoir, by heat exchange with the fluid flowing in said secondary circuit, before its injection into said secondary reservoir; the method comprises a step of cooling gas leaving said first or second compressor by heat exchange with the cooled liquefied gas contained in said secondary tank; the method comprises a step of pre-cooling the gas leaving said first or second compressor, before cooling in said secondary tank, by heat exchange with natural evaporation gas taken from said main tank; the method comprises a step of preheating the natural evaporation gas taken from said main tank before being compressed by said first or second compressor; the process comprises, before the filling of said second flask, a step of lowering the pressure and / or the temperature of the gas intended to supply said second flask; the method comprises a step of injecting liquefied gas cooled in said main tank, by means of said second pipe; this injection makes it possible to participate in the cooling of the liquefied gas contained in the main reservoir, in order to limit the production of BOG. the method comprises a step of conveying gas from said second flask to said second compressor; this gas can be used in the installation after compression. The invention also relates to a fuel gas supply method of a power generation installation, in particular on board a ship, by means of a device as described above, characterized in that it comprises a liquefied gas sampling step A contained in said main tank, said liquefied gas being taken from said first line at a sampling temperature, a step B of expanding said withdrawn gas at a lower expansion pressure than a vapor pressure; saturating said gas sampled at said sampling temperature, so that a part of said withdrawn gas vaporizes under the effect of the expansion, and that a remaining part of said sampled gas remains liquid and is cooled to a temperature lower than that of said sampling temperature, in particular because said sampled gas is cooled to a saturation temperature at said expansion zone, a step C of filling said first balloon and separating, in particular by gravity, into said first balloon, said liquefied gas with respect to said cooled liquid gas, a step F of supplying the secondary reservoir with gas cooled liquefied from said first flask, and storage of said cooled liquefied gas in said secondary reservoir, - step G of natural evaporation gas sampling in said main tank and preheating thereof, - a compression step H at the times of evaporation gas from said first flask and preheated natural evaporation gas, a step I of supplying said plant with said compressed gases.

The method according to the invention may comprise one or more of the following steps or characteristics, taken separately from each other or in combination with each other: steps A, B, C and F are carried out continuously; simultaneously with steps A, B, C and F, simultaneously with step G, or simultaneously with steps A, B, C, F and G, the process comprises a step of withdrawing cooled liquefied gas from said secondary reservoir and injecting this gas into said main tank in order to cool the liquefied gas contained in this main tank; the injection of cooled liquefied gas is carried out directly in the liquefied gas and / or in the evaporation gas of said main tank;

According to a second aspect, the invention proposes a device for cooling natural evaporation gas for an energy production installation, in particular on board a vessel, characterized in that it comprises: optionally, a tank main liquefied gas storage system and having a first natural evaporation gas outlet, - liquefied gas cooling means, - a cooled liquefied gas secondary tank configured to store liquefied gas cooled by said cooling means, and a first heat exchange circuit having an inlet for connection to said first outlet of said main reservoir for the circulation of natural evaporation gas in said circuit, said first circuit being configured to cooperate with said secondary reservoir so that said natural evaporation gas passing through said first circuit is cooled by liquid gas cooled choke stored in said secondary tank or from said secondary tank.

The main reservoir is optional insofar as it can be considered as part or not of the device according to the invention. The device can for example be delivered without a main tank which is not part of the device. Alternatively, the device once mounted on a ship for example, is associated with a main tank which is part of the device according to the invention.

The solution thus proposes an improvement of the management of the BOG in a device adapted to the needs for example of a ship, by cooling this BOG, and allowing: - to limit the capacity of the means used for the cooling to that necessary for the management surplus NBOG instead of the one needed to manage a peak production NBOG, - optimize the utilization rate of these means that can be used continuously, the cold source, such as cooled liquefied gas, can be stored if necessary, - ensure that the refrigerating capacity produced is used correctly when necessary.

The solution is suitable for any type of means that cool a fluid. The fluid here is BOG from the tank, cooled in the secondary tank and finally returned to the tank where it will be in a cooled state.

The device according to the invention may comprise one or more of the following characteristics, taken separately from each other or in combination with each other: a first separation balloon, one input of which is connected to an output of said first circuit for the purpose of supplying said first flask with cooled natural evaporation gas and recondensed natural evaporation gas forming cooled liquefied gas, said first flask comprising a first natural evaporation gas outlet and a second cooled liquefied gas outlet intended to be connected to said main tank for injection of cooled liquefied gas into said main tank; said second tank is configured to contain the cooled liquefied gas at a pressure greater than an operating pressure of said first tank; the device comprises at least a first compressor, an inlet of which is connected to said first natural evaporation gas outlet of said main tank and / or to said first outlet of natural evaporation gas of said first tank; said cooling means comprise a second heat exchange circuit which is intended to cooperate by heat exchange with liquefied gas of said secondary tank or from said secondary tank, and in which circulates a cooling fluid for the cooling of said liquefied gas ; cooled liquefied gas is thus directly generated in said secondary tank and the generation of cooled liquefied gas; said cooling means comprise: a second balloon, an inlet of which is connected to a first end of a first pipe whose second end is intended to be immersed in the liquefied gas contained in said main tank, said first pipe being able to feed said second balloon liquefied gas, and a second pipe having a first end is connected to a first cooled liquefied gas outlet of said second balloon, and a second end is connected to said secondary tank for supplying cooled liquefied gas said tank secondary; said second balloon is a separation and / or expansion balloon; the device comprises a first heat exchanger of which a primary circuit has an inlet connected to a liquefied gas outlet of said main tank, and a cooled liquefied gas outlet, and a secondary circuit has an inlet connected to said first pipe and a connected output at the entrance of said second balloon; said second heat exchanger is not immersed in the liquefied gas of said main tank, nor mounted in said main tank; the output of the primary circuit of said second heat exchanger is connected to an inlet of said secondary tank, for the purpose of supplying cooled liquefied gas from said secondary tank; the device is devoid of components other than pumps and / or pipes, immersed in the liquefied gas contained in said main tank; said inlet of said primary circuit is connected to an outlet of a third pump intended to be immersed in the liquefied gas of said main tank; the device comprises: a first pump connected to said second end of said first pipe, and intended to be immersed in said liquefied gas contained in said main tank, so as to force the circulation of liquefied gas through said first pipe from said main tank until said second balloon, and a second pump connected to said second conduit so as to force the flow of liquefied gas cooled from said second balloon to said secondary reservoir. said first conduit includes said vaporizing means; the device comprises at least a second compressor having an inlet connected to said first natural evaporation gas outlet of said main tank; said second compressor has an output connected to said input of said first circuit; said inlet of said second compressor is further connected to a second gas outlet of said second flask and / or a second gas outlet of said first flask; said input of said second compressor is connected to the output of said first compressor; said first or second compressor has an outlet adapted to supply combustible gas, in particular to said installation; said input of said first circuit is connected to said output of said first or second compressor by a primary circuit of a second heat exchanger, said second heat exchanger having a secondary circuit having an input connected to said first evaporation gas outlet natural of said main tank, and an output of which is connected to said inlet of said first or second compressor; said secondary tank is connected to a first end of a third pipe of cooled liquefied gas, a second end of which is intended to be connected to said main tank, said third pipe being able to convey at least a portion of said cooled liquefied gas from said secondary tank up to that main tank; said third pipe comprises a plunger intended to be immersed in the liquefied gas contained in said main tank, and / or a spray bar located in said main tank, for the injection of cooled liquefied gas into said main tank; said input of said first circuit is connected to said output of at least one compressor, such as said first or second compressor, by a primary circuit of a second heat exchanger, said second heat exchanger having a secondary circuit of which an input is connected to said first natural evaporation gas outlet of said main reservoir, and an output of which is connected to said inlet of said first or second compressor; there can thus be a prior exchange (the exchange must be prior since the natural evaporation gas is less cold than the cooled liquid gas) between the totality of the natural evaporation gas (part of which goes to the installation) and a compressed part of this natural evaporation gas (the surplus beyond the consumption of the installation which is recondensed); the device is devoid of components other than pumps and / or pipes, immersed in the liquefied gas contained in said main tank.

The effects and advantages described in the foregoing in relation to the characteristics of the device of the first aspect of the invention are naturally applicable to the same characteristics of the device of the second aspect, and vice versa.

The present invention also relates to a vessel, in particular for transporting liquefied gas, comprising at least one device as described above.

The method according to the invention may comprise one or more of the following steps or characteristics, taken separately from each other or in combination with each other: the method comprises: a step of compressing gas leaving said first outlet of said main tank and / or a step of compressing gas leaving said second outlet of said first flask, and / or a step of compressing gas leaving said second outlet of said second flask; the method comprises a precooling step of the compressed gas, before it is cooled in said secondary tank, by heat exchange with natural evaporation gas taken from said main tank and circulating in said secondary circuit of said second exchanger; the method comprises a step of preheating natural evaporation gas taken from said main tank, by heat exchange with the fluid flowing in said primary circuit of said second exchanger, before the compression of this gas; the method comprises a step of cooling the liquefied gas contained in said secondary tank; the method comprises a step of expanding liquefied gas so that a portion of said gas vaporizes under the effect of the expansion, and that a remaining portion of said gas remains liquid and is cooled, the process comprises a step of filling said second balloon and separating, in particular by gravity, into said first balloon, said vaporized gas with respect to said cooled liquid gas; the method comprises a step of supplying cooled liquefied gas from said secondary reservoir; the method comprises a step of preheating liquefied gas taken from said main tank by heat exchange with the fluid circulating in said primary circuit of said first exchanger, after the expansion and before the injection of said liquefied gas into said second balloon; the method comprises a step of cooling liquefied gas taken from said main tank by heat exchange with the fluid flowing in said secondary circuit of said first exchanger, before its injection into said secondary tank.

The effects and advantages described in the foregoing in relation to the features and process steps of the first aspect of the invention are naturally applicable to the same features and process steps of the second aspect, and vice versa. The invention also relates to a method for cooling liquefied gas and / or gas for evaporation of liquefied gas for an energy production installation, in particular on a ship, by means of a device as described below. above, characterized in that it comprises: a step A for preparing liquefied gas cooled in said secondary reservoir, a step B for withdrawing liquefied gas cooled in said secondary reservoir, a step C for injecting said liquefied gas cooled in said evaporation gas and / or in said liquefied gas contained in the main tank. The invention also relates to a fuel gas supply method of a power generation installation, in particular on board a ship, by means of a device as described above, characterized in that it comprises monitoring at least one gas consumption parameter by said installation, and when the value of said parameter is greater than a predetermined threshold, a step of preparation and storage of cooled liquefied gas, in particular in said secondary tank, when the value of said parameter is less than a predetermined threshold, a step of recondensation of natural evaporation gas produced in excess in said main tank

The method may include a step of cooling the gas contained in said main tank from said cooled liquefied gas to limit the production of natural evaporation gas.

The predetermined threshold may possibly vary, for example during a voyage of the ship. Functionally, this threshold may correspond to the flow rate of NBOG to be withdrawn from the main reservoir so as not to have to control the pressure of the latter.

Advantageously, cooled liquefied gas is prepared when the production of natural evaporation gas is insufficient to meet the consumption of gas by said installation.

Preferably, liquefied gas is cooled by sampling, expansion, and phase separation of liquefied gas contained in said main tank.

The slowing down of the natural evaporation can be done in several ways: by pouring the cooled liquid gas into the tank (for example by the spray bar of the liquid gas cooled in the tank, or by simple exit in the main tank), or by an exchange of cold (that is to say by an exchanger) between the natural evaporation gas and the cooled gas which allows the recondensation of the natural evaporation gas (possibly also returned to the tank).

The fact that the liquid gas is undercooled makes it possible not to generate evaporation gas when it is desired to slow down the natural evaporation. Storage makes it possible to cope with significant recondensation needs with a secondary reservoir of limited capacity (for example a liquefaction unit is very expensive and its cost depends on its capacity).

Alternatively, the cooled gas is stored in the main tank in order to condense natural evaporation gas in this tank, particularly when the available amount of natural evaporation gas in this tank is greater than the need of the facility. Since the cooled gas has a higher density than the rest of the gas in the main tank, it is necessary, for example, to cool / recondense the natural evaporation gas from the liquid gas at the bottom of the main tank, for example below the liquid outlet. or exchanger for example. For example, an exchanger may be provided at this location or a pipe may be provided for bringing the cooled gas stored at this location to a heat exchanger (located for example outside the tank) with natural evaporation.

Advantageously: said natural evaporation gas is condensed by heat exchange with said cooled liquefied gas, and / or said natural evaporation gas is compressed before said heat exchange, and / or said natural evaporation gas is decompressed after said heat exchange, and / or said natural evaporation gas undergoes phase separation after said decompression.

The features and steps of the device and method of the first aspect of the invention may be combined with those of the device and method of the second aspect, and vice versa.

BRIEF DESCRIPTION OF THE FIGURES The invention will be better understood and other details, characteristics and advantages of the present invention will appear more clearly on reading the description which follows, given by way of nonlimiting example and with reference to the appended drawings. in which: - Figure 1 is a schematic view of a first embodiment of a device according to the invention, which here a ship, - Figures 2 to 6 are schematic views corresponding to Figure 1 and illustrating the steps of a method according to the invention, - Figure 7 is a schematic view of a second embodiment of a device according to the invention, which here a ship, - Figure 8 is a schematic view of a third embodiment of a device according to the invention, which equips a ship here, - Figures 9 and 10 are schematic views of a fourth embodiment of a device according to the invention, which team here a ship , and illustrating steps of a method according to the invention - Figure 11 is a schematic view of a fifth embodiment of a device according to the invention, which here a ship, - Figure 12 is a view schematic of a sixth embodiment of a device according to the invention, which team here a ship, - Figure 13 is a schematic view of a seventh embodiment of a device according to the invention, which team here a ship.

DETAILED DESCRIPTION

FIG. 1 shows a first embodiment of a device 10 according to the invention which can be considered as allowing a cooling of liquefied gas and / or a cooling of natural evaporation gas of liquefied gas.

The device 10 is particularly suitable but not exclusively for the supply of fuel gas to a ship, such as a liquefied gas transport vessel. The device 10 can thus be used to supply fuel gas to an installation 12 for producing energy, in particular on a ship.

A vessel has a tank 14 or more tanks 14 for storing liquefied gas. The gas is, for example, methane or a mixture of gases comprising methane. The or each reservoir 14 may contain gas in liquefied form at a predetermined pressure and temperature, for example at atmospheric pressure and a temperature of the order of -160 ° C. One or more tanks 14 of the ship can be connected to the installation 12 by a device 10 according to the invention. The number of tanks is thus not limiting. It is for example between 1 and 6. Each tank 14 can have a capacity of between 1,000 to 50,000m3.

In what follows, the expression "the tank" will have to be interpreted as "the or each tank".

The reservoir 14 contains liquefied gas 14a as well as gas 14b resulting from an evaporation, in particular a natural evaporation, of the liquefied gas 14a in the tank 14. Naturally, the liquefied gas 14a is stored at the bottom of the tank 14 while the 14b evaporation is located above the level of liquefied gas in the tank, schematically represented by the letter N.

In what follows, "LNG" denotes liquefied gas, that is to say gas in liquid form, "BOG" denotes evaporation gas, "NBOG" denotes natural evaporation gas, and "FBOG" means forced evaporation gas, these acronyms being known to those skilled in the art because they correspond to the initials of the associated English expressions.

In the embodiment shown in Figure 1, pumps 16a, 16b are immersed in the LNG tank 14, and are preferably located at the bottom of the tank to ensure that they are fed only LNG.

The pumps 16a, 16b are here two in number. The pump 16a is connected to an end, here below, of a pipe 18. The pump 16b is connected to an end, here below, of a pipe 20. In a variant, there may be more pumps of each type, for example to provide redundancy of 16a and 16b or use existing pumps such as spray pumps already on a ship (in which case, the function of 16b could be provided by the four spray pumps, each of which has four separate tanks.

The pipe 20 comprises an upper end connected to an LNG droplet spray ramp 22 situated in the upper part of the tank 14, above the level N. The ramp 22 is thus configured to spray LNG droplets in the NBOG. This makes it possible to force the recondensation of the NBOG in the tank 14. The pump 16b is configured to force the circulation of LNG in line 20, from the bottom of the tank 14 to the ramp 22 and to ensure that the LNG is pulverized in the form of droplets. In practice, a gaseous sky can be present in the main tank while the NBOG can circulate in the pipes.

The pump 16a is configured to force the flow of LNG in the pipe 18 from the bottom of the tank 14 to a balloon 24 connected to one end, for example greater, of the pipe 18. The pipe 18 comprises depressurization means 19 , such as a valve JT, so as to reduce the pressure of the LNG circulating in the pipe 18 before reaching the balloon 24. Advantageously, the means 19 are configured so that the pressure of the LNG flowing in the pipe 18 is lowered to the operating pressure of the balloon 24. The means 19 comprise for example a valve JT (as described below).

The circulation of the LNG in the pipe 18 and through the depressurization means 19 therefore results in at least partial vaporization of the LNG before feeding the balloon 24.

The balloon 24 is thus intended to be supplied with partially vaporized LNG coming from the tank 14. The operating pressure inside the balloon 24 is lower than the storage pressure of the LNG inside the tank 14. 24 balloon in LNG can cause a complementary vaporization of LNG, resulting on the one hand by the generation of FBOG in the balloon 24, and the cooling of LNG remaining in the balloon, which is called "cooled liquefied gas". The flask 24 contains gas in liquefied form at a predetermined pressure and temperature.

The balloon 24 thus contains cooled liquefied gas 24a and gas 24b resulting from an evaporation, forced here, of the liquefied gas 14a from the tank 14. Naturally, the cooled liquefied gas (or LNG) 24a is stored at the bottom of the balloon 24 while the evaporation gas (or FBOG) 24b is located above the level of liquefied gas in the balloon 24, schematically represented by the letter L.

The balloon 24 comprises three fluid communication ports, namely an LNG inlet connected to the pipe 18, an FBOG output and an LNG output.

The output of FBOG is connected to an input of a compressor 26, an output of which is connected to a compressor 28. The compressors 26, 28 may be two independent compressors or two compression stages of the same compressor. The compressors 26, 28 can thus be shared.

The compressor 26 is here used to apply the operating pressure inside the balloon 24. It is thus configured to depressurize the balloon 24 relative to the tank 14. The pressure difference between them may be such that it is sufficient to force the flow of LNG from the tank to the balloon 24. In the latter case, it is therefore understood that the pump 16a is optional. The conditions imposed by the compressor 26 on the balloon 24 are determined to generate LNG in the expansion tank.

When the amount of LNG in the balloon 24 is too large and a threshold level is likely to be reached, LNG can be transferred from the LNG outlet of the balloon 24 to an LNG inlet of a secondary tank 30.

The balloon 24 and the secondary tank 30 are here connected by a pipe 31 comprising for example a valve 33 and a pump 35. The pump 35 is configured to force the flow of LNGs from the tank 24 to the secondary tank 30. The pump 35 is particularly useful when the tank 30 is overpressurized with the balloon 24. The secondary tank 30 contains LNG at a predetermined pressure and temperature.

The secondary tank 30 is configured to store the excess LNG produced in the tank 24. The tank 30 thus contains cooled liquefied gas 30a and gas 30b resulting from evaporation, here natural, liquefied gas 14a from the tank 14 Naturally, the cooled liquefied gas (or LNG) 30a is stored at the bottom of the secondary tank 30 while the evaporation gas 30b is located above the level of liquefied gas in this tank, schematically represented by the letter M.

The secondary reservoir 30 comprises an output of LNGs. In the example shown, this outlet is connected by a pipe 32 on the one hand to the spray boom 22 of the tank 14 or each tank 14, and on the other hand to a plunger 34 intended to be immersed or immersed in the LNG tank. It is thus understood that LNG can supply the spray boom 22 for the purpose of spraying LNG droplets into the BOG of the tank 14, and the LNG can supply the plunger 34 with a view to the injection of LNGs directly into the LNG of the tank. tank 14.

The pipe 32 can be connected to the LNG outlet of the secondary tank 30 by a valve 36. The pipe can be connected to the plunger 34 and the ramp 22 by a three-way valve 38.

The secondary reservoir 30 is here used to cool a fluid, such as a gas or a liquid, which is here BOG main tank 14. A heat exchange circuit 40 is here associated with the secondary reservoir 30. The association should here be understood in the broad sense, the circuit 40 may for example be a serpentine pipe immersed in the LNG contained in the secondary tank 30. The circuit 40 could alternatively be located outside the tank 30. The circuit 40 is configured so that heat exchanges take place between the fluid flowing in the circuit 40 and the LNG contained in the secondary reservoir 30. The fluid flowing in the circuit 40 is generally hotter than the LNG which thus cools the fluid during its operation. circulation in the circuit 40. The circuit comprises an input and an output. The input of the circuit 40 is connected to an output 45 of BOG main tank 14, which is here at an upper end of the tank. The BOG output 45 of the reservoir 14 is connected to an input of a secondary circuit 42a of a heat exchanger 42, an output of which is connected to the input or to an input of the compressor 28.

The output of the compressor 28 is generally connected to the installation 12 for its supply of fuel gas. Part of the fuel gas leaving the compressor 28 can be withdrawn and re-routed via a pipe 44 which can be connected to the outlet of the compressor 28 via a three-way valve 46.

The compressor 28 is configured to compress the gas (such as the NBOG from the tank) to a working pressure adapted to its use in the plant 12.

Line 44 is connected to an input of a primary circuit 42b of exchanger 42, an output of which is connected to the input of circuit 40.

The output of the circuit 40 is connected by a line 48 to a balloon 50 separate from the balloon 24. The line 48 comprises a valve 52, which is preferably a Joule-Thomson effect valve, for the purpose of reducing the temperature of the gas by adiabatic expansion.

A relaxation of Joule-Thomson is a stationary and slow laminar relaxation carried out by passing a flow of gas through a buffer (wadding or raw silk in general) in an insulated pipe and horizontal, the pressure reigning on the left and on the right buffer being different. For real gases, the relaxation of Joule-Thomson is generally accompanied by a variation of temperature: it is the Joule-Thomson effect. The exchanger 42, the circuit 40, and the valve 52 cool and (re) partially condense the BOG.

The balloon 50 is intended to separate the BOG remained in gaseous form 50b BOG (re) condensed 50a before supplying the tank 14 in BOG (re) condensed. Naturally, the recondensed BOG 50a is stored at the bottom of the flask 50 while the evaporation gas (or BOG) 50b is located above the level of liquefied gas in the flask 50, schematically represented by the letter O.

The balloon 50 comprises three fluid communication ports, namely a BOG input connected to the line 48, a BOG gas output and a BOG (re) condensed output. The BOG gas outlet is here connected to the inlet of the compressor 28. The condensed BOG (re) outlet is here connected to the plunger 34, the pipe 32 and / or the spray bar 22 for the purpose of BOG injection. (re) condensed in the reservoir 14.

The vacuum evaporation means formed by the following elements, the pump 16a, the depressurization means 19, the tank 24 and the compressor 26, make it possible to recover the latent heat of vaporization which is generally spent in an evaporator of the technique. prior to producing FBGG and the cooling capacity which is used in particular to cool the LNG contained in the main tank 14.

The LNG forms a refrigerating capacity that can be stored in the secondary tank 30 when it is not necessary, for example during phases where the quantity of NBOG produced is insufficient to meet the demand.

The latent heat recovery vaporization is obtained through the device 10 above and in particular the balloon 24, whose operating pressure is less than that of the reservoir 14 which is for example between -20mbarg and 250mbarg (mbar gauge - or between -20 and 350mbarg, or between -20 and 700mbarg). The operating pressure of the balloon 24 is preferably between 300 and 800mbara (absolute mbar).

The LNG from the tank 14 at a saturation equilibrium corresponding to the storage pressure of the LNG in the tank 14, is conveyed to the balloon 24 which is in depression with respect to the tank 14. Therefore, this LNG is in a state of overheating when it is depressurized by the means 19 and, to reach a saturation equilibrium, it releases its excess heat by vaporization. The LNG is then separated into LNGs and FBOG inside the balloon 24 in proportions depending in particular on the operating pressure of the balloon 24.

For example, with an operating pressure of 300mbara, the evaporation rate of the LNG feeding the balloon 24 is between 9.5 and 10%. At 800mbara, this rate is between 2.3 and 3%. The remaining part is a liquid cooled to a temperature corresponding to the saturation equilibrium at the operating pressure of the balloon 24. For example, with an operating pressure of 300mbara, the LNG is cooled to a temperature of between -172. and -175 ° C (temperature drop from -12 to -15 ° C), and at 800mbara, the LNG is cooled to a temperature between -163 and -164 ° C (temperature drop from -3 to - 4 ° C).

Then, the LNG can be evacuated through the pump 35, preferably to the secondary tank 30. The pump 35 can be used to increase the pressure of the LNG. The storage of LNG in the secondary tank 30 keeps the cooling capacity.

In operation, the vaporized part of the LNG feeding the balloon 24 will accumulate in this balloon. In order to control the pressure at a predetermined value in the balloon 24 (for example between 300 and 800mbara), the FBG0 produced in the balloon 24 is preferably continuously extracted. This is done by the compressor 26, which is configured to suck the gas contained in the tank 24, with an inlet pressure corresponding to the operating pressure of the tank 24 and an outlet pressure which is for example similar to the pressure of the tank. Storage of the LNG in the tank 14. The gas thus treated is then easy to use since it is at a pressure similar to that of the NBOG produced in the tank 14 and can supply, with this NBOG, the same compressor 28. This compressor 28 is configured to produce fuel gas directly usable in the installation 12, for example for the supply of propulsion machinery of the ship.

With the device 10 presented in the foregoing, to meet the gas consumption by the installation 12, the NBOG produced in the tank 14 is conveyed to the compressor 28 which compresses it to the operating pressure. The additional BOG required to meet the demand is produced by forced vaporization of the LNG supplying the balloon 24, then successively supplying the compressors 26 and 28. The pump 16 may be necessary to feed the balloon 24 with LNG from the tank 14. , especially when the height of the tank or the level N is between 10 and 50m - in this case, the only depression of the balloon 24 may indeed be insufficient to circulate the LNG passively in the pipe 18.

The balloon 24 must thus be fed with a sufficient flow of LNG to meet, with the NBOG, fuel consumption consumption needs of the installation 12. For example, the additional flow of FBOG that would be produced in the balloon 24 could be between 0 and 4000 kg / h. Accordingly, depending on the composition of the LNG and the operating pressure of the balloon 24, the flow from the tank 14 to the balloon 24 could be between 0 and 17.5 t / h.

The LNG generated in the balloon 24 is stored in the secondary tank 30. The tank 30 is configured to store and store the LNG and is therefore advantageously thermally insulated. The pressure in the secondary reservoir 30 is for example between 0.3bara and 10bara, to benefit from flexibility in the management of the pressure. The temperature of the LNG in the tank 30 is close to that of the LNG in the balloon 24, and is for example between -175 to -161 ° C. This is necessary, for example during phases where the NBOG is in excess, the LNG contained in the secondary tank 30 can be routed in line 32 to the spray boom 22, to spray droplets of LNG in the BOG contained in the tank 14 and thus cool the BOG. It can also be re-injected by the diver 34 into the tank LNG in order to directly cool this LNG.

The NBOG which would be produced in excess of the demand of the installation 12, is taken and conveyed to the compressor 28. It is then redirected by the valve 46 to the circuit 40 of the secondary reservoir 30 in which it is cooled. by heat exchange with the previously stored LNG, as previously explained. Then, the excess NBOG is directed to the valve 52 through which it will be depressurized to reach a pressure close to the storage pressure in the reservoir 14. For example, if the reservoir is an atmospheric reservoir, the excess NBOG can be depressurized at a pressure between 0 and 1barg. Next, the excess NBOG feeds the balloon 50, where it undergoes a phase separation, in BOG (re) condensed and BOG gas. The BOG gas is conveyed by the pipe 51 to the compressor 28 in the same way as the NBOG that would be produced in the tank 14. The BOG (re) condensed is injected into the tank 14 for the storage of LNG.

FIGS. 2 to 6 illustrate phases of operation of the device of FIG. 1, which may correspond to the speed phases of the ship equipped with this device.

The process for cooling liquefied gas is described here in three phases: 1. Phase where the quantity of NBOG is insufficient, also called FBOG phase (FIGS. 2 and 3), for example when the vessel is sailing at a speed requiring more BOG to complete the NBOG product in the reservoir (s) 14. Additional BOG or FBOG will be provided by the device 10 and cold power will be generated. 2. Phase in which the NBOG produced is in excess (Figures 4 and 5), for example when the ship is sailing at a low speed or is anchored, the excess of NBOG to be managed in a safe and respectful manner. environment. 3. Phase in which the main tank 14 of the ship is cooled (FIG. 6), for example before loading after the return voyage (during which management of the BOG is generally not necessary because the tank or tanks 14 are practically empty) . 1. Phase where the amount of NBOG is insufficient, also called FBOG phase (Figures 2 and 3)

Figure 2 illustrates steps of the first phase in which FBGO and LNG are jointly produced by the device.

In order to control the pressure in the tank 14, NBOG is taken from this tank through the outlet 45 and then feeds the compressor 28, which will produce combustible gas at a permissible pressure for the installation 12, for example of the order from 6-7bars, 15-17bars or 300-315bars. In order to supplement the quantity of gas and meet the consumption needs of the installation 12, the LNG of the tank 14 is conveyed by the pump 16a and the pipe 18 to the depressurization means 19 where the LNG undergoes a depression up to the operating pressure of the balloon 24. The LNG reaches the balloon 24 at the operating pressure of this balloon and, because of the saturation equilibrium displacement induced by the pressure differential between the balloon 24 and the tank 14, a part LNG vaporizes (flash phenomenon) between the depressurization means 19 and the balloon and the rest is cooled to the saturation temperature of the LNG at the operating pressure of the balloon. Sufficient flow must be taken from the tank 14, as explained above. The FBOG contained in the balloon 24 is then evacuated and compressed by the compressor 26 at the storage pressure of the LNG in the tank 14. Then, the FBOG is again compressed by the compressor 28 to reach the pressure required for the installation 12 In order not to fill the balloon in excess 24, the LNG of this balloon is conveyed to the secondary tank 30, in particular when the LNG filling rate of the balloon reaches a certain threshold level, for example 50%.

Figure 3 illustrates further steps of the first phase in which LNG is stored in the secondary tank 30.

In the case where the capacity of the secondary tank 30 is not sufficient to store the LNG produced, LNG contained in the tank 30 can be transferred to the bottom of the tank 14, through the pipe 32 and the plunger 34, to cool the LNG of the tank 14 below the saturation temperature of the LNG at the storage pressure in the tank 14. 2. The phase in which the NBOG produced is in excess (FIGS. 4 and 5)

Figure 4 illustrates steps of the second phase in which excess BOG is recondensed.

The NBOG produced in the tank 14 is in sufficient quantity or more than sufficient to meet the needs of the installation 12. In order to control the pressure in the tank 14, the BOG is taken from this tank and feeds the compressor 28 to reach the pressure required for installation 12. The excess BOG that can not be consumed by the installation is conveyed from the outlet of the compressor 28 to the exchanger 42 in which it undergoes cooling by heat exchange with the NBOG cold taken directly from the tank 14 through the outlet 45. The excess BOG is then sent to the circuit 40 of the secondary tank 30 where it is again cooled by heat exchange with LNG stored in this tank, as explained above. Then, the excess BOG is depressurized by the valve 52 and feeds the balloon 50 where the BOG (re) condensed by the exchanger 42, the circuit 40 and the valve 52 is separated from the BOG gas. The remaining BOG gas is returned to the compressor 28 to supply the installation 12.

Figure 5 illustrates steps of the second phase, in which LNG is pulverized.

Instead of recondensing the excess of NBOG through the dedicated line, it is possible to transfer the LNG contained in the secondary reservoir 30 to the pipe 32 and then to the spray boom 22, to directly recondense the BOG contained in the reservoir. 14. 3. Phase in which the vessel's main tank is cooled (Figure 6)

Figure 6 illustrates steps of the last phase.

Typically, the re-liquefaction terminals, where the ship loads its cargo, require a cold temperature in the tank 14 before loading, in order to limit the amount of LNG that would be instantly vaporized (flash). This is generally done by spraying by means of the ramp 22, and the associated pump 16b, the LNG already contained in the tank 14 for cooling the BOG of this tank. With the device 10, this operation can be performed by supplying the ramp 22 with LNGs from the secondary tank 30, and therefore LNG colder than that contained in the tank 14. In the same way, when the BOG contained in the tank 14 is not sufficient to supply the installation 12, the LNG contained in the secondary tank 30 can be regenerated in the same way as during the first phase.

FIG. 7 represents an alternative embodiment of the device which differs from that of FIG. 1 in that it comprises another heat exchanger 60. The heat exchanger 60 comprises two circuits, respectively primary 60a and secondary 60b.

The secondary circuit 60b comprises an input connected to the pipe 18, here downstream of the depressurization means 19. The secondary circuit 60b comprises an output connected to the LNG inlet of the balloon 24.

The primary circuit 60a comprises an input connected by a three-way valve 62 respectively to the pump 16b and to the spray bar 22 of the reservoir 14. The primary circuit 60a comprises an output connected to an LNG inlet of the secondary reservoir 30.

The secondary circuit 60b is a cold circuit, the fluid circulating in this circuit and in this case the depressurized LNG, being intended to be heated by circulation in this circuit so as to vaporize it (in FBOG). The primary circuit 60a is a hot circuit, the fluid flowing in this circuit and in this case the LNG from the tank 14, being intended to be cooled by circulation in this circuit. The circuit 60a may not allow, however, to vaporize the heavier components (ethane, propane, etc.). It is understood that the depressurization upstream of the secondary circuit 60b makes it possible to lower the vaporization temperature, which makes it possible to generate FBOG from a heat exchange with the LNG taken from the tank and circulating in the primary circuit. FBOG vaporization requires a supply of heat supplied by the LNG circulating in the primary circuit, so it is a cooling source for the cooling of LNG circulating in the primary circuit.

LNG from the tank 14 is thus conveyed by the pump 16a to the depressurization means 19 and then circulates in the secondary or cold circuit of the exchanger 60. In the meantime, LNG from the tank is conveyed by the pump 16b until To the primary or hot circuit of the exchanger 60. Therefore, the heat exchange between these circuits results in: the heating of depressurized and partially vaporized LNG, with a view to continuing its vaporization, which is then conveyed to the balloon in order to undergo a phase separation, - the cooling of LNG which feeds the secondary reservoir 30 to be stored there for later use.

Then, the device functions as initially described in relation with FIGS. 1 to 6. The impacts of exchanger 60 are here: pump 16a can be sized to circulate only a predetermined maximum quantity of LNG, with a view to training FBOG sufficient to meet the needs of the installation 12, in addition to the NBOG. This task could be carried out by the fuel pump generally installed in a ship, - the capacity of the balloon 24 can be reduced to the extent that the feed rate of LNG can be lower (only the additional FBOG flow would be used to reach the fuel gas demand of the plant 12), - because of the temperature pinch in the heat exchanger, the cooling capacity production is lowered (approximately 15% loss on the basis of an operating pressure of 500 mbara) - the flow of LNG and LNG flowing with this solution is lower, therefore, the energy consumption of the pumps is reduced, which reduces the energy consumption of the system

FIG. 8 shows another embodiment of a device 110 according to the invention which can be considered as allowing a cooling of liquefied gas and / or a cooling of natural evaporation gas of liquefied gas.

The device 110 is particularly suitable but not exclusively for the supply of fuel gas to a ship, such as a liquefied gas transport vessel. The device can thus be used to supply fuel gas to an installation 112 for producing energy on board a ship.

A vessel comprises a tank 114 or several tanks 114 for storing liquefied gas. The gas is, for example, methane or a mixture of gases comprising methane, for example liquefied natural gas. The or each reservoir 114 may contain gas in liquefied form at a predetermined pressure and temperature, for example at atmospheric pressure and a temperature of the order of -160 ° C. One or more of the tanks 114 of the ship can be connected to the installation 112 by a device 110 according to the invention. The number of tanks is thus not limiting. It is for example between 1 and 6. Each tank 114 can have a capacity of between 1,000 to 50,000m3.

In what follows, the expression "the tank" should be interpreted as "the or each tank".

The reservoir 114 contains liquefied gas 114a as well as gas 114b resulting from an evaporation, in particular a natural evaporation, of the liquefied gas 114a in the tank 114. Naturally, the liquefied gas 114a is stored at the bottom of the tank 114 while the Evaporation 114b is located above the level of liquefied gas in the tank, schematically represented by the letter N.

In what follows, "LNG" designates liquefied gas, that is to say gas in liquid form, "BOG" designates evaporation gas, "NBOG" designates natural evaporation gas, and "FBOG Refers to forced evaporation gas, these acronyms being known to those skilled in the art because they correspond to the initials of associated English expressions.

In the embodiment shown in FIG. 8, the tank 114 comprises a LNG droplet spray ramp 122 which is situated in the upper part of the tank, above the level N. The ramp 122 is thus configured to spray droplets of LNG in the BOG. This makes it possible to force the recondensation of the BOG in the tank 14.

The device 110 here comprises cooling means 170 which are associated with a secondary reservoir 130 LNG storage.

The cooling means 170 comprise, for example, a heat exchange circuit 172 associated with the tank 130. The secondary tank 130 contains LNGs at a predetermined pressure and temperature.

The secondary tank 130 is configured to store LNGs. The reservoir 30 thus contains cooled liquefied gas 130a as well as gas 130b resulting from evaporation of the liquefied gas 130a. Naturally, the cooled liquefied gas (or LNG) 130a is stored at the bottom of the secondary tank 130 while the evaporation gas 130b is located above the level of liquefied gas, schematically represented by the letter M.

The secondary reservoir 130 includes an output of LNGs. In the example shown, this outlet is connected by a pipe 132 on the one hand to the spray boom 122 of the tank 114 or each tank 114, and on the other hand to a plunger 134 intended to be immersed or immersed in the tank. LNG Tank 114. It is thus understood that LNG can supply the spray boom 122 for the spraying of LNG droplets in the BOG of the tank 114, and the LNG can supply the plunger 134 for the injection of LNGs. directly into the tank LNG 114.

The pipe 132 can be connected to the LNG outlet of the secondary tank 130 via a valve 136. The pipe can be connected to the plunger 134 and to the ramp 122 via a three-way valve 138.

The secondary reservoir 130 is here used to cool a fluid, such as a gas or a liquid, which is here BOG main tank 114. Another heat exchange circuit 140 is here associated with the secondary reservoir 130. The association of each circuit 140, 172 to the secondary tank 130 must here be understood in the broad sense, the circuits 172 and 140 may for example be serpentine pipes immersed in the LNG contained in the secondary tank 130. These circuits may alternatively be located outside the tank 130. The circuit 140 is configured so that heat exchanges take place between the fluid flowing in the circuit and the LNG contained in the secondary tank 130. The fluid flowing in the circuit 140 is generally warmer LNG which thus cools the fluid during its circulation in the circuit 140. The circuit comprises an input and an output. The input of the circuit 140 is connected to a BOG output 145 of the main tank 114, which is here at an upper end of the tank. The BOG 145 output of the tank 140 is connected to an input of a secondary circuit 142a of a heat exchanger 142, an output of which is connected to an input of a compressor 128.

The output of the compressor 128 is generally connected to the installation 112 for its supply of fuel gas. Part of the fuel gas leaving the compressor 128 can be withdrawn and re-routed through a pipe 144 which can be connected to the outlet of the compressor 128 via a three-way valve 146.

The compressor 128 is configured to compress the gas to a service pressure adapted to its use in the installation 112.

The pipe 140 is connected to an input of a primary circuit 142b of the exchanger 142, an output of which is connected to the input of the circuit 140.

The output of the circuit 140 is connected by a line 148 to a balloon 150. The line 148 comprises a valve 152, such as a Joule-Thomson effect valve, for the purpose of reducing the temperature of the gas by adiabatic expansion. The exchanger 142, the circuit 140 and the valve 152 condense (in other words: (re) liquefy) part of the BOG.

The balloon 150 is intended to separate the BOG thus (re) condensed from the BOG remained in gaseous form.

The balloon 150 thus contains BOG (re) condensed (by the condensing line comprising for example the exchanger 142, the circuit 140 and the valve 152) 150a as well as the BOG gas 150b. Naturally, condensed BOG 150a is stored at the bottom of flask 150 while BOG gas 150b is located above the level of liquefied gas in flask 150, schematically represented by the letter O.

The balloon 150 comprises three fluid communication ports, namely a BOG input connected to the line 148, a BOG gas output and a liquid BOG output. The condensed BOG outlet is here connected to the inlet of the compressor 126 via a pipe 151. The liquid BOG outlet is here connected to the plunger 134, the pipe 132 and / or the spray boom 122 for the storage of LNG in the tank 114.

FIG. 9 represents an alternative embodiment of the device 110 which differs from that of FIG. 8 by its cooling means 170.

Thus, the cooling means 170 comprise a pump 116a immersed in the LNG of the tank 114, and preferably located at the bottom of the tank to ensure that it is fed only LNG.

The pump 116a is connected to an end, here below, of a pipe 118. The pipe 118 comprises an upper end connected to an LNG inlet of the secondary tank 130 for the supply of LNGs in this tank. Line 118 passes through or includes a cold generator, such as a vacuum evaporator, which may include a balloon associated with a compressor, as illustrated in the previous embodiment.

The pump 116a is configured to force the flow of LNG in the line 118 from the bottom of the tank 114 to the secondary tank 130, for the LNG feed of the secondary tank 130 and storage therein.

In the devices of Figures 8 and 9, the solution is the integration of cooling means 170 in the environment of a ship to make the best use of this equipment to meet the needs of the ship. The cooling means 170 are such that, in use: for the type represented in FIG. 9, LNG is conveyed from the tank 114, by the pump 116a, to the cooling means 170 where it is cooled and then injected into the secondary reservoir 130 where it is stored; if the capacity of the tank 130 is not sufficient for this storage, LNGs can be sent to the line 132 and then by the plunger 134 inside the tank 114, which makes it possible to cool the LNG in the tank 114; for the second type represented in FIG. 8, the cooling means 170 directly cool the LNG stored in the secondary tank 130 by being directly in contact with this LNG, in order to generate LNGs.

In both cases, the result is that LNG is stored in the secondary tank 130. The temperature of the LNG is preferably between -180 and -160 ° C, which corresponds to a temperature drop of the LNG between -0, 5 and -20 ° C typically. Because of the heat input into the secondary tank 130, some of the LNGs can evaporate and turn into BOG 130b. If the pressure inside the secondary reservoir 130 reaches a predetermined threshold, then it can be controlled by removing part of the BOG by the compressor 126. The secondary reservoir 130 is designed according to its use, and for example has a capacity between 50 to 500m3 for the management of the BOG during travel, or from 1,500 to 10,000m3 for BOG management during anchoring (2 to 5 days). The pressure in the secondary reservoir 130 is for example between 0.3bara and 10bara, to benefit from flexibility in the management of the pressure and the evaporation gas 130b.

The cooling means 170 can be operated independently of the solution and its environment. Preferably, the cooling means 170 are in continuous operation, when cooling capacity is immediately necessary or not.

When necessary, LNG can be sent to tank 114 by means of line 132 and plunger 134, for example to control the pressure or temperature of the LNG contained in tank 114.

Typically, the pressure in the tank 114 is monitored by removing NBOG from the tank 114 by aspirating the NBOG by means of the compressor 126 through the NBOG outlet 145 of the tank 114. Next, the NBOG from the compressor 126 is used to supply the installation 112. If the load of the installation 112 is not sufficient to consume all the NBOG, then there is excess NBOG that must be managed. In this case, it is preferable to act only on the excess NBOG rather than on the LNG or all the NBOG contained in the tank 114, as previously described. Thanks to the solution, the excess NBOG coming from the compressor 126 to the operating pressure of the installation 112 (for example 6-7bars or 15-17bars or 300-315bars depending on the type of installation of the ship) is sent to the heat exchanger 142 through which it will be cooled by heat exchange with NBOG taken from the outlet of NBOG 145 in the tank 114. Next, the excess NBOG is sent to the heat exchange circuit 140 of the tank 130, through it will be cooled by heat exchange the LNG contained in the tank 130. Then, the excess NBOG is depressurized by the valve JT 152 at the operating pressure of the balloon 150, before feeding the balloon 150. The balloon 150 is regulated at a pressure close to the storage pressure in the tank 114. Thanks to the arrangement of the BOG condensing line (which comprises the heat exchanger 142, the circuit 140, the valve JT 152 and the balloon 150) , part of the NBOG surplus is condensed. Finally, the condensed NBOG recovered in the balloon 150 is reinjected into the tank 114, through the plunger 134. By (re) condensing the NBOG, it is possible to lower the pressure of the NBOG in the tank 114.

The advantages of this device are numerous and for example: the cooling means 170 can process all the excess NBOG and operate continuously at an average capacity. Typically, the cooling means 170 are sized either to handle the maximum excess of NBOG, then operate at lower capacities to handle the actual variations of excess NBOG, or at a balanced capacity and the excess of NBOG beyond that capacity is lost. With the device 110, the cooling means 170 can be sized according to the average excess capacity of NBOG while being able to handle all the surplus NBOG. For a typical ship, the average excess NBOG is in the range of 25 to 50% maximum NBOG excess. This flexibility to absorb the variations, on the one hand, of the production of cooling capacity, and on the other hand, of the cooling capacity needs, is granted thanks to the secondary tank 130 which is capable of storing LNGs colder than LNG. stored in the tank 114. By doing so, the cold power is concentrated in the LNGs and ready to be used when it is necessary, while it is diluted inside the consequent volume of the tank 114 in the prior art .

Typically, the cold power is used to spray LNG into the tank 114. In doing so, the vapor phase in the tank 114 is cooled and partially condensed. In terms of energy, this is not ideal because part of the excess NBOG can be used to supply the installation 112. Thanks to the device 110, part of the NBOG is used to power the installation 112 and the cold power is used only on the excess NBOG. For a typical ship, the gas consumption during anchoring is in the range of 15 to 30% of the NBOG. - Thanks to the compressor 126 that equips the ship, the surplus NBOG is compressed at an inlet pressure of the installation 112 (typically 6-7bar, 15-17 bar or 300-315bar), then cooled by LNG and phased before returning to the main tank 114. This is more efficient than spraying LNGs in the vapor phase of the main tank 114, since it allows the excess NBOG to be further cooled and condensed to a greater extent by the pressure difference. - Some cooling means can be used in particular conditions. For example, the vacuum evaporator described in the foregoing can only generate cold from additional FBOG needed in addition to the NBOG to power the installation 112. With the device 110, the generated cold power can be used when and where it is necessary.

FIGS. 9 and 10 illustrate operating phases of the device of FIG. 9, which are naturally applicable to the device of FIG. 8, and which may correspond to the operating phases of the ship equipped with this device. 1. Check tank conditions (pressure and temperature) - figure 9; 2. Management of excess NBOG - figure 10. 1. Check tank conditions (pressure and temperature) - figure 9.

In the case where the secondary tank 130 does not need to be supplied with LNG from the tank 114 (for example, the energy requirements are provided by another energy source) and the conditions of the tank 114 must be controlled. (eg wetting pressure or temperature before loading), then LNG contained in the secondary tank 130 can be used to cool the LNG contained in the tank 114, by routing it through the line 132 and the plunger 134. 2. Management excess NBOG - Figure 10.

As previously described, the excess NBOG can be managed by circulating it through the condensation line formed by the exchanger 142, the heat exchange circuit 140, the JT valve 152 and the balloon 150.

Figure 11 shows an alternative.

Since the installation requires a gas supply typically at an inlet pressure greater than the storage pressure in the tank 114, the compressor 126 makes it possible to route the NBOG to a pressure admissible by the installation 112. The NBOG is warmed up during this compression. Preferably, the exchanger 142 is used to recover a portion of the cold from the tank 114. This is a possibility for better performance, but is not fundamental and therefore not essential. It is therefore removed in the embodiment of FIG. 11. An output of the three-way valve 146 is therefore directly connected to the input of the circuit 140, and the output of NBOG 145 of the reservoir is directly connected to the input of the compressor 126.

Figure 12 shows an alternative embodiment of the device which differs from that of Figure 9 in that it comprises another heat exchanger 180. The heat exchanger 180 comprises two circuits, respectively primary 180a and secondary 180b.

The secondary circuit 180b comprises an inlet connected to a pump 182 immersed in the LNG contained in the secondary tank 130, and an outlet connected to an LNG inlet in the tank 130, for the reinjection of LNGs into the tank after the it has exchanged calories with the fluid flowing in the primary circuit of the exchanger 180. The primary circuit 180 is comparable to the circuit 140 for heat exchange described above.

The primary circuit 180a is a hot circuit, the fluid circulating in this circuit and in this case the compressed BOG, being intended to be cooled by circulation in this circuit. The secondary circuit 180b is a cold circuit, the fluid flowing in this circuit and in this case the LNG from tank 330, being intended to be cooled by circulation in this circuit.

FIG. 13 represents an alternative embodiment of the device 10 which differs from that of FIG. 1 in that the balloon 24 and the secondary tank 30 are communized to form and define a single same tank 90 for forced vaporization of LNG coming from the tank 14 and storage of LNGs so produced.

The first table below gives examples of values for various operating parameters of the device according to the invention, for various ranges (wide, median and optimal).

The second table provides the same types of parameters but targeted on more common compositions of liquefied gas and in particular liquefied natural gas, such as methane or a gas mixture containing methane.

Depending on the level of filling of the main tank, the hydrostatic pressure varies at the lower end of the pipe 18 (the pump is generally at a stable depth).

The temperature of the liquefied gas in the flask 24 is equal to the "temperature of the BOG cooled by the circuit 40 (° Q" minus 2 ° C for example, which corresponds to the "pinching" of the exchanger.

The fraction of gas evaporated after depressurization is given by the formula: X = (H1, u-H1, d) / (Hv, d-H1, d) in which: X is the mass percentage of vaporized liquid,

Hl, d (J / Kg) is the enthalpy of the upstream liquid at the upstream temperature and pressure,

Hv, d (J / Kg) is the enthalpy of the gas vaporized at the downstream pressure and corresponding to the saturation temperature, and

H1, d (J / Kg) is the enthalpy of the residual liquid at the downstream pressure and corresponding to the saturation temperature.

Claims (24)

1. Device (10, 110) for cooling natural evaporation gas for an installation (12, 112) for producing energy, in particular on board a ship, characterized in that it comprises: optionally a main reservoir (14, 114) for liquefied gas storage and having a first outlet (45, 145) of natural evaporation gas, - means (170) for cooling liquefied gas, - a secondary reservoir (30, 130 ) a cooled liquefied gas configured to store liquefied gas cooled by said cooling means, and - a first heat exchange circuit (40, 140) having an inlet for connection to said first outlet of said main tank for the circulation of natural evaporation gas in said circuit, said first circuit being configured to cooperate with said secondary reservoir so that said natural evaporation gas passing through said first the circuit is cooled by cooled liquefied gas stored in said secondary tank or from said secondary tank. 2. Device (10, 110) according to the preceding claim, wherein it further comprises: - a first separation flask (50, 150) having an input connected to an output of said first circuit (40, 140) in order to feeding said first flask with cooled natural evaporation gas and recondensed natural evaporation gas forming cooled liquefied gas, said first flask having a first natural evaporation gas outlet and a second cooled liquefied gas outlet for be connected to said main tank for the injection of cooled liquefied gas into said main tank. 3. Device (10, 110) according to one of the preceding claims, wherein it comprises at least a first compressor (26, 126) whose inlet is connected to said first natural evaporation gas outlet of said main tank (14). 114) and / or said first natural evaporation gas outlet of said first flask (50, 150). 4. Device (10, 110) according to one of the preceding claims, wherein said cooling means comprises a second circuit (172) for heat exchange which is intended to cooperate by heat exchange with liquefied gas of said secondary tank (30, 130) or from said secondary reservoir (30, 130), and wherein a coolant circulates for cooling said liquefied gas and generating the cooled liquefied gas. 5. Device (10, 110) according to one of claims 1 to 3, wherein said cooling means comprise: - a second balloon (24) having an inlet connected to a first end of a first pipe (18, 118) of which a second end is intended to be immersed in the liquefied gas contained in said main tank (14, 114), said first pipe being able to supply said second balloon with liquefied gas, and - a second pipe (31) of which one first end is connected to a first cooled liquefied gas outlet of said second flask, and a second end of which is connected to said secondary tank for supplying cooled liquefied gas from said secondary tank (30, 130). 6. Device (10, 110) according to the preceding claim, wherein it comprises a first heat exchanger (60), a primary circuit (60a) has an inlet connected to a liquefied gas outlet of said main tank (14), and an outlet is connected to an inlet of said secondary tank (30), for the supply of liquefied gas to said secondary tank, and a secondary circuit (60b) has an inlet connected to said first pipe (18) and an output connected to the inlet of said second balloon (24). 7. Device (10, 110) according to claim 5 or 6, wherein it comprises: - a first pump (16a, 116a) connected to said second end of said first pipe (18, 118), and intended to be immersed in said liquefied gas contained in said main tank (14, 114), thereby forcing the flow of liquefied gas through said first line from said main tank to said second balloon (24), and - a second pump (35) connected said second conduit (31) for forcing the flow of liquefied gas cooled from said second balloon (24) to said secondary reservoir (30, 130). 8. Device (10, 110) according to one of claims 5 to 7, wherein said first pipe (18,118) includes spray means (19). 9. Device (10, 110) according to one of the preceding claims, wherein it comprises at least a second compressor (28, 128) whose input is connected to said first outlet (45, 145) of natural evaporation gas said main reservoir (14, 114), said second compressor having an output connected to said input of said first circuit (40, 140). 10. Device (10, 110) according to the preceding claim, in accordance with one of claims 5 to 8, wherein said inlet of said second compressor (28, 128) is further connected to a second gas outlet of said second balloon (24) and / or a second gas outlet of said first flask (50, 150). 11. Device (10, 110) according to claim 9 or 10, in dependence on claim 3, wherein said input of said second compressor (28) is connected to the output of said first compressor (26). 12. Device (10, 110) according to one of claims 9 to 11, wherein said first or second compressor (26, 28, 126) comprises an output capable of supplying combustible gas, in particular to said installation (12, 112). . The device (10, 110) according to one of claims 9 to 12, wherein said input of said first circuit (40, 140) is connected to said output of said first or second compressor (26, 28, 126) by a circuit primary (42b, 142b) of a second heat exchanger (42, 142), said second heat exchanger having a secondary circuit (42a, 142a) having an input connected to said first gas outlet (45, 145); natural evaporation of said main tank (14, 114), and an outlet of which is connected to said inlet of said first or second compressor. 14. Device (10, 110) according to one of the preceding claims, wherein said secondary reservoir (30, 130) is connected to a first end of a third pipe (32, 132) of cooled liquefied gas, a second end is intended to be connected to said main tank (14, 114), said third pipe being adapted to convey at least a portion of said cooled liquefied gas from said secondary tank to said main tank. 15. Device (10, 110) according to the preceding claim, wherein said third pipe comprises a plunger (34, 134) intended to be immersed in the liquefied gas contained in said main tank (14, 114), and / or a ramp spraying apparatus (22, 122) in said main reservoir for injection of cooled liquefied gas into said main reservoir. 16. Ship, in particular liquefied gas transport, comprising at least one device (10, 110) according to one of the preceding claims. 17. A method for supplying fuel gas to a plant (12, 112) for producing energy, in particular on board a ship, by means of a device (10, 110) according to one of claims 1 to 15, characterized in that it comprises monitoring at least one gas consumption parameter by said installation, and when the value of said parameter is greater than a predetermined threshold, a step of preparation and storage of cooled liquefied gas, for example in said secondary tank, when the value of said parameter is below a predetermined threshold, a natural gas evaporation gas recondensation step produced in excess in said main tank. 18. The method according to the preceding claim, wherein cooled liquefied gas is prepared when the production of natural evaporation gas is insufficient to meet the consumption of gas by said installation. 19. Method according to the preceding claim, wherein liquefied gas is cooled by sampling, expansion, and phase separation of liquefied gas contained in said main tank. 20. The method according to one of claims 17 to 19, wherein said cooled liquefied gas is stored in the main tank in order to condense natural evaporation gas in this tank, particularly when the available amount of natural evaporation gas. in this tank is greater than the need for said installation. 21. The method according to one of claims 17 to 20, wherein said natural evaporation gas is condensed by heat exchange with said cooled liquefied gas. 22. Method according to the preceding claim, wherein said natural evaporation gas is compressed before said heat exchange. The method of claim 21 or 22, wherein said natural evaporation gas is decompressed after said heat exchange. 24. The method according to the preceding claim, wherein said natural evaporation gas undergoes a phase separation after said decompression.