RU2769600C2 - Device and method for cooling liquefied gas and/or gas of natural steaming from liquefied gas - Google Patents

Abstract

FIELD: gas industry.

SUBSTANCE: invention relates to the cooling of steamed gas. Device (10) for cooling natural steaming gas for energy generation plant (12), in particular onboard the vessel, includes main tank (14) for storage of liquefied gas, including the first outlet branch pipe for natural steaming gas (45), means (170) for cooling liquefied gas, auxiliary tank (30) for cooled liquefied gas, made with the possibility of storage of liquefied gas cooled by means of cooling, first heat exchange circuit (40) including an inlet branch pipe, made with the possibility of connection to the first outlet branch pipe of the main tank for circulation of natural steaming gas in the circuit. The first circuit is made with the possibility of communication with the auxiliary tank, so that natural steaming gas passing through the first circuit is cooled by means of cooled liquefied gas stored in the auxiliary tank or coming from the auxiliary tank.

EFFECT: simplification of cooling natural waste gas.

20 cl, 13 dwg

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

The invention relates to a device and method for cooling liquefied gas and/or natural stripping gas from liquefied gas for an energy production plant, in particular on board a ship, for example an liquefied gas carrier, or installations that use liquefied gas.

PRIOR ART

The prior art includes, in particular, document EP-A1 2 670 274.

To facilitate the transport of a gas such as natural gas over long distances, the gas is typically liquefied (and becomes liquefied natural gas - LNG) by cooling to cryogenic temperatures, such as -163°C at atmospheric pressure. The liquefied gas is then loaded into specialized vessels.

An liquefied gas carrier, such as a methane tanker, is provided with an energy generation plant to meet the energy demand for the operation of the vessel, in particular to propel the vessel and/or generate electricity for on-board equipment.

This type of plant usually includes heat engines consuming the gas leaving the evaporator, which is supplied from a cargo of liquefied gas transported in a tank or tanks of a ship.

Document FR-A-2 837 783 describes the supply to this kind of evaporator and/or other systems required for propulsion by means of a pump immersed in the ship's tank at its bottom.

To limit the evaporation of a liquefied gas, it is known to store it under pressure in a tank so as to move along the liquid-vapor equilibrium curve of the liquefied gas, correspondingly increasing its evaporation temperature. Therefore, LPG can be stored at higher temperatures while limiting gas evaporation.

However, natural evaporation of the gas is unavoidable: this phenomenon is known as natural stripping gas (NBOG) as opposed to forced stripping gas (FBOG). The gas that evaporates naturally in the ship's tank is generally used to power the above plant. In the case (first case) in which the amount of naturally volatilized gas is not sufficient to meet the fuel gas requirement of the plant, a pump immersed in the tank is operated to supply the fuel gas obtained by forced evaporation. In the case (second case) in which the amount of volatilized gas is too large in relation to the demand of the plant, the excess gas is usually combusted in the gas flaring plant, which is a waste of fuel gas.

In the current state of the art, tanks are being improved in such a way that the natural evaporation rates (evaporation rate , BOR) of liquefied gases become lower and lower, while ship equipment shows ever higher productivity. In the above first and second cases, the consequence is that there is a very large difference between the amount of gas obtained by natural stripping and the amount of gas required by the ship's installation.

Therefore, there is a growing interest in solutions for cooling the liquefied gas contained in a storage tank and controlling the boil-off gas produced in this tank, such as reliquefaction and cooling devices, such as those described in WO-A1-2016/075399. The idea on which this document is based is to provide a liquefied gas refrigeration device that makes it possible to limit the natural evaporation of the liquefied gas while maintaining it in a thermodynamic state allowing long-term storage. However, the heat exchange technology described in the aforementioned document is expensive and relatively inefficient, and has other disadvantages, which will be detailed below.

In addition, natural stripping gas (NBOG) production is affected by a number of parameters, including fluid movement and environmental conditions. The energy requirements of a ship also vary greatly, according to the operations performed and the speed of the ship. Therefore, an efficient boil-off gas (BOG) management solution may be difficult to implement because the excess amount of NBOG can vary greatly.

The present invention provides an improvement to the current state of the art that is simple, effective and economical.

SUMMARY OF THE INVENTION

The first object of the present invention provides a device for cooling liquefied gas, in particular for a power generation plant on board a ship,

characterized in that it includes

- an optional main tank for storing liquefied gas,

- the first refrigerated liquefied gas separation drum, the inlet of which is connected to the first end of the first pipe, the second end of which is intended for immersion in the liquefied gas contained in the specified main tank, preferably in the lower part of the tank, and the specified first pipe is configured to supply liquefied gas into the indicated first drum,

- a means for reducing the pressure in the said first drum relative to the said main tank, configured to apply in the said first drum a working pressure lower than the pressure in the said main tank,

- evaporation means installed on said first pipe and / or said inlet of said first drum so that at least some part of the liquefied gas supplied to said first drum, called boil-off gas, evaporates, and at least another part (for example, the remainder ) liquefied gas, referred to as refrigerated liquefied gas, is cooled to saturation temperature at a specified operating pressure in said first drum, said first drum being capable of separating said vaporized gas and refrigerated liquefied gas, and

- means for supplying said cooled liquefied gas contained in said first drum to said main tank in order to cool the gas which has been liquefied and/or is in the form of a gas contained in said main tank.

Here, it is the liquefied gas that is cooled or, rather, additionally cooled, which is used to cool and regulate the temperature of the liquefied gas contained in the main tank.

The first drum acts as a vacuum evaporator and is connected to the first compressor which acts as a vacuum evaporator compressor. It is known that the evaporation or reduction of gas pressure releases freezing energy. The evaporating means can thus be regarded as a cooling means. In addition, the terms "evaporation means", "pressure reducing means" and "pressure reducing means" have similar or even identical meanings in the context of the present invention. According to the invention, the evaporator is mounted on the first pipe and/or the inlet connecting this first pipe to the first drum. The first drum may also form an (additional) evaporation means, as described below.

Thus, the invention proposes to replace the heat exchanger in the prior art with a vacuum evaporator, which makes it possible to obtain a higher cooling capacity and, consequently, to improve the cooling efficiency of the gas contained in the main tank, which has been liquefied and/or is in the form of a gas.

The main tank is optional in that it may or may not be considered an integral part of the device according to the invention. The device may, for example, be supplied without any main tank, which therefore does not form part of the device. Alternatively, after installation on a ship, for example, the device will be connected to the main tank, which thus forms part of the device in accordance with the present invention.

The advantage is that there is no heat exchanger (the disadvantage of which is the loss of cooling due to the pinch effect) operating during the expansion or evaporation phase. In the prior art, when using a heat exchanger of this kind, all the light fraction is completely evaporated, in particular due to the heat exchanger, which evaporates the light gas fraction remaining liquid after pressure reduction. However, the pressure reduction and the heat exchanger are not sufficient to vaporize the heavy fraction as well.

In the present application, the heavy fraction and the light fraction mean, respectively, heavy gases, or gases with a high molecular weight, and light gases, or gases with a low molecular weight. In one embodiment, the liquefied gas is liquefied natural gas. In this case, the light gas is methane. Liquefied natural gas may also contain a small amount of nitrogen in the light fraction. The smaller heavy fraction includes, for example, for LPG, propane, butane and ethane (and therefore evaporates at a higher temperature or at a pressure lower than, for example, the operating pressure). In liquefied gas, heavy fractions range from 5.2% to 49.8% of the total mass of liquefied gas. The molecular weights of heavy fractions exceed the molecular weights of light fractions by 25–500%.

The improvements offered by this device are numerous and include, for example, the following benefits:

- simpler architecture, easier handling and safer use thanks to a cooling process that can take place entirely outside the main tank,

- increased efficiency by suppressing the pinch effect, which can occur in the prior art due to the heat exchanger, as for example described in the application WO-A1-2016/075399; taking into account the operating pressure and the temperature fluctuations associated with it, the pinch effect from 1 to 2 °C leads to a loss of 15% of the cooling capacity,

- cooling capacity is produced in the form of refrigerated liquefied gas, which can be supplied and used as needed, or even stored for later use; this is a particular advantage, since this power can be produced by extracting energy from the forced stripping gas in the stages of the absence of natural stripping gas (NBOG), corresponding to stages in which heating power is needed rather than cooling power,

- contrary to the contrary, given the typical dimensions of a main tank, in particular on a ship, the volume of gas stored in a tank of this kind, and the dimensions of the necessary cooling equipment described in the above-mentioned earlier application, the cooling capacity produced by this equipment is not sufficient for its storage and subsequent use,

- liquefied gas is intended to undergo phase separation in a drum, after which only the gas that can be used in the plant is intended to be pumped out using a pressure reducing device such as a compressor; therefore, there is no risk of liquid droplets entering the compressor, which could damage it; taking into account the range of operating pressures, temperatures and composition of the liquefied gas, in most cases the liquefied gas will not completely evaporate in the heat exchanger, as for example described in the aforementioned earlier application; for example, the fluid ratio in the original architecture at 120 mbar is between 0.12 and 32% inclusive, and at 800 mbar (it is not possible to consider a pressure of 950 mbar, as proposed in an earlier application, due to the pinch effect in the heat exchanger) it is is in the range from 0.8 to 92% inclusive (high fluctuations due to different compositions of liquefied gas),

- in the earlier application, the entire flow required to be supplied to the plant, i.e. destined for the consumer, must pass through the compressor, which is not necessary in the case of the invention, in which only the necessary amount of forced stripping gas is used in addition to the amount of gas produced natural stripping; the compressor capacity is therefore reduced, thus reducing initial capital and operating costs; in addition, since each component of the device introduces losses, in general, the limitation of the flows circulating in the device is more effective; finally, the proposed device is easy to connect to a normal ship consuming installation, therefore, limiting the impact on the existing environment and giving more flexibility in the design of ship engines using fuel gas;

- the drum is preferably located outside the main tank, which simplifies the device and makes it safe.

In general, compared to a conventional ship-mounted device, in which additional boil-off gas (BOG) is produced by supplying liquefied gas to the heat exchanger using a pump, in this case, the device reduces the total energy consumption for evaporation by 31 - 38%. The main purpose is to obtain cold through the use of evaporative energy, which is usually a consumable item on the ship. Depending on the characteristics of the vessel, in particular the speed profile, the efficiency of the mechanisms, etc., the device allows the production of a cooling capacity of up to 175% of the heat generated during the voyage of the vessel (including the return journey, commercial use and waiting for the call into the fairway).

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

In the context of the present invention, the "bottom" of a tank means a position located less than one meter from the bottom wall of the tank, this bottom wall being the wall of the tank closest to the center of the Earth in operation. Each pump is preferably also as close to the bottom as possible to operate at the lowest possible filling level (distance from the bottom is limited because a pump too close to the bottom can be difficult to bring to service).

The device according to the present invention may have one or more of the following features, either alone or in combination with each other:

said first drum is a separation drum and/or an expansion drum;

- at least part of the specified first drum and/or at least part of the specified first pipe and/or at least part of the specified means of evaporation placed or intended to be placed in the specified main tank;

- the specified first drum is made with the possibility of supplying only liquefied gas;

- the pressure of the liquefied gas in said first pipe is preferably greater than the hydrostatic pressure created by the submerged part of this first pipe in said main tank;

- the diameter of said first pipe upstream of said pressure reducing means should preferably be as small as possible in order to limit the cooling of the liquefied gas in this pipe (limiting the loss of cold);

- said first pipe is preferably designed in such a way that the liquefied gas entering said main tank remains liquid up to said pressure reducing means; although the pressure drops in the first pipe due to hydrostatic pressure due to the reduced immersion depth in the main tank, the pressure remains high enough to keep all of the gas in a liquid state;

- the pressure in the first pipe at the inlet to the pressure reducing means is, for example, about 1 bar; the liquefied gas, having only slightly warmed up in the first pipe, still remains at a temperature at which it is liquid at a pressure of about 1 bar (for example, at a temperature of about -160 °C);

- said evaporation means includes a valve, for example a throttle valve (Joule-Thomson valve), and/or a part of the first pipe located, in particular, downstream of the valve;

- the liquefied gas used preferably evaporates (for the most part or more than 80%, even 90%) immediately after the valve, in said part of the first pipe; the liquefied gas is also cooled in this part of the pipe due to the reduction in pressure due to the effect of "flash" evaporation (spontaneous decrease in pressure);

- this part of the pipe can have a larger diameter than the first part of the pipe located in front of the valve, in particular to obtain a sufficient flow rate, since the boil-off gas occupies a larger volume;

- alternatively, evaporation can occur mostly or even exclusively (more than 80%) in said first drum, if the part of the pipe between the valve and the first drum is reduced in diameter or missing; in this case, if the first drum does not have sufficient volume, continuous operation may not be possible; therefore, it would be necessary to wait until the evaporation and cooling of the liquefied gas, at a temperature just below the boiling point at the new pressure, after a "momentary" reduction in pressure, would have been completed, in order to empty the first drum, in particular into the auxiliary tank mentioned below; furthermore, in this case, it would be possible, in particular, to replace a valve, such as a throttle valve, with a simple two-state (all or nothing, i.e. 100% closed/100% open) valve;

said pressure reducing means includes at least a first compressor, the inlet of which is connected to the first outlet of gas from said first drum, and the outlet of which can supply fuel gas, in particular to said plant, said first compressor able to suck in at least some of the specified gas evaporating in the specified first drum, and create the specified operating pressure in the specified first drum; instead or in addition to this, the pressure reducing means includes at least one pump, the inlet pipe of which is connected to the outlet pipe of the liquid from the specified first drum; in this embodiment, at least one compressor can be used to draw in the vaporized gas contained in said first drum;

- said supply means includes a second pipe, the first end of which is connected to the second outlet of the refrigerated liquefied gas of the specified first drum, and at least one second end of which is intended for discharge into the specified main tank, and the specified second pipe can enter at least parts of said refrigerated liquefied gas from said second drum to said main tank; connection of the first drum with the specified main tank through the specified second pipe may be direct or indirect; in other words, the second pipe may include other fluid communication components, be associated with such components, or be divided into sections between which such components are located; this may apply to all pipes mentioned in the context of the present invention;

- gas in liquid and/or gaseous form can be introduced into said main tank, in particular through said second pipe; a mixture of gas and steam can be introduced into the main tank; if this mixture is reintroduced into the bottom of the tank, the gas portion of the mixture will tend to recondense due to the hydrostatic pressure of the gas and the temperature of the liquefied natural gas in the main tank; this may slow down the reduction of pressure in the main tank;

device includes

- a first pump connected to said second end of said first pipe and designed to be immersed in said liquefied gas contained in said main tank, preferably in the lower part of the tank, so as to circulate the liquefied gas through said first pipe into said first drum; alternatively, the device does not have such a first pump; this is, for example, possible if the first drum and the first pipe are located inside said first tank;

the device comprises a second pump connected to said second pipe so as to circulate at least a portion of said refrigerated liquefied gas through said second pipe from said first drum to said main tank; alternatively, this second pump would not be necessary, for example, in the case of intermittent operation, when the first drum is supplied with liquefied gas to a predetermined filling level, and then the pressure in it is reduced to cause cooling of the liquefied gas and partial evaporation, which will lead to to increase the pressure in the specified first drum to a value essentially close to the pressure in the main tank, and sufficient to ensure that the use of a second pump is not necessary;

- the first pipe is equipped with an all-or-nothing valve and is made with the possibility of closing, for example, under reduced pressure created in the specified first drum;

- the first or second pump may be a fuel pump or a vessel drier pump; this type of pump is usually able to provide a maximum flow of about 25-30 t/h; alternatively, a pump with a higher maximum flow rate can be used, in particular as a first pump, which, for example, would be able to provide a maximum flow rate of 300 t/h, or preferably even up to 2500 t/h;

- the system formed by the first drum, the first compressor and the first pump acts as a means of vacuum evaporation (or vacuum evaporator); in general, in the case of the present invention, the system formed by the drum, compressor and pump is similar to the vacuum evaporation means;

- the means of evaporation is preferably made with the possibility of reducing the pressure of the gas to the operating pressure of the first drum;

said second outlet of said first compressor is connected to an inlet of a second compressor whose outlet may supply fuel gas to said plant;

said second pipe includes or is connected to a dip pipe designed to be immersed in the liquefied gas contained in said main tank and/or to a spray manifold in said main tank for introducing cooled liquefied gas into said main tank; the refrigerated liquefied gas can therefore be introduced into the gas and/or into the liquefied gas contained in the main tank;

said second outlet of said first drum is connected to the first inlet of the auxiliary tank so that the cooled liquefied gas is supplied to and stored in that tank;

- the auxiliary tank is configured to contain said refrigerated liquefied gas at a pressure higher than said operating pressure in said first drum; thus, the auxiliary tank has a higher pressure than the first drum, for example, at atmospheric pressure; thus, the auxiliary tank can be less expensive in that it can be designed to store a large volume of gas, which is an advantage of this auxiliary tank; thus, the cooled gas can be stored in the first drum if plant requirements exceed the natural evaporation rate, and then drained into the main tank in such a way as to slow down natural evaporation if plant requirements are less than the natural evaporation rate;

- the refrigerated liquefied gas contained in said auxiliary tank may be considered as subcooled liquefied gas; "subcooled" means that the gas is at a temperature strictly lower than the boiling point (i.e., saturation temperature) at the pressure to which the gas is subjected; in the auxiliary tank, the liquefied gas is under such pressure that it can be considered supercooled;

- the auxiliary tank acts as a cooling fluid heat exchanger, in particular boil-off gas (BOG);

said second pump is located between said second outlet of said first drum and said first inlet of said auxiliary tank;

said auxiliary tank includes a first outlet for at least part of said refrigerated liquefied gas connected to said second pipe, said second pipe being capable of passing at least portions of said refrigerated liquefied gas from said auxiliary tank to said main tank;

said device includes at least one heat exchange circuit configured to cool the fluid circulating in said circuit using at least a portion of the refrigerated liquefied gas stored in said auxiliary tank or coming from said auxiliary tank; this heat exchange circuit may be located in the auxiliary tank, adjacent to it or in connection with the auxiliary tank, or at a distance from this auxiliary tank; the refrigerated liquefied gas pipe may, for example, be used to supply said heat exchange circuit, which may form part of a separate heat exchanger; alternatively, the refrigerated liquefied gas used to cool the fluid circulating in said heat exchange circuit may come from another source, such as the main tank or the first drum;

- the combination of said auxiliary tank and said heat exchange circuit allows the stripping gas to be processed with very high efficiency, since the pinch effect associated with the heat exchanger is small compared to the temperature difference between the stripping gas (gas in the vapor phase at the inlet of the auxiliary tank at temperature, for example, between -80 °C and -160 °C inclusive, or, more precisely, between -100 °C and -140 °C inclusive) and liquefied gas, in particular due to the fact that liquefied gas is cooled; of course, in the absence of an auxiliary tank, the same advantage can be obtained by heat exchange with the cooled gas from said first drum or from the main tank; in other words, the refrigerated liquefied gas may be stored in the auxiliary tank, the first drum and/or the main tank;

said heat exchange circuit includes an inlet pipe connected to an outlet pipe of natural stripping gas from said main tank; in this context, said heat exchange circuit can process the flash gas in the main tank with very high efficiency, since the pinch effect associated with the heat exchanger is small compared to the temperature difference between the flash gas and the liquefied gas, in particular due to the cooling of the liquefied gas. gas;

said inlet of said circuit is connected to said outlet of at least one compressor, such as said first or second compressor, which receives the stripping gas from said outlet of said main tank; the stripping gas is thus compressed (which increases its temperature) before entering the heat exchanger or heat exchange circuit with the refrigerated liquefied gas;

- said inlet of said circuit is connected to said outlet of at least one compressor, for example the first or second said compressor, by means of a primary circuit of a first heat exchanger, said first heat exchanger including a secondary circuit whose inlet is connected to said gas outlet natural stripping of the specified main tank, and the outlet of which is connected to the inlet of the specified first or second compressor; the stripping gas in the main tank will be heated when it enters said secondary circuit, which is not a problem since it must be heated in any case if it is used to supply the plant; the heat exchange preferably takes place in advance between the entire volume of stripping gas, part supplied to the plant, and the compressed part of this stripping gas, the surplus from plant consumption, which is recondensed. Heat exchange must take place in advance, as the natural stripping gas is less cold than the refrigerated LPG

Said heat exchange circuit comprises an outlet connected to an inlet of a second drum, said second drum including a first refrigerated liquefied gas inlet connected to said second pipe for introducing the refrigerated liquefied gas into said main tank; alternatively, the device may be configured to reinject into the main tank, for example, at the bottom of the tank, the gaseous portion of the mixture, which will tend to re-condense due to the hydrostatic pressure of the gas and the temperature of the liquefied gas in the main tank;

- said second drum is a phase separation drum;

said outlet of said circuit is connected to said inlet of said second drum by means of a valve, such as a throttle valve (Joule-Thomson valve), to reduce the temperature of the gas by means of adiabatic expansion; thus, the stripping gas can expand; compression/reduction of pressure on both sides of the heat exchanger or heat exchange circuit can give a lower temperature of the stripping gas, and therefore more stripping gas for condensation;

- the device includes a second heat exchanger, the primary circuit of which has an inlet connected to the outlet of the third pump intended for immersion in liquefied gas in the specified main tank, and the outlet of the cooled liquefied gas, and the secondary circuit has an inlet connected to the specified the first pipe, and the outlet pipe connected to the inlet pipe of the specified first drum;

said second heat exchanger is not immersed in liquefied gas in said main tank and is not installed in the main tank;

- the outlet pipe of the primary circuit of the specified second heat exchanger is connected to the inlet pipe of the specified auxiliary tank for supplying the specified auxiliary tank of the refrigerated liquefied gas;

- the device does not contain any components other than pumps and/or pipes immersed in the liquefied gas contained in said main tank;

said liquefied gas contains at least the so-called pure fraction, which includes pure gas or body, and said cooled liquefied gas and said boil-off gas comprise at least one pure fraction. If the liquefied gas is liquefied natural gas, this kind of pure fraction may consist of methane.

In this application, "pure" refers to a single body or chemical substance, as opposed to a mixture of bodies or substances. Said pure gas is, for example, a light gas or a heavy gas.

The present invention also relates to ships, in particular for the transport of liquefied gas, and includes at least one device as described above.

The present invention also relates to a method for cooling a liquefied gas for an energy production plant, in particular on board a ship, using the apparatus described above, characterized in that it comprises

step A of receiving the liquefied gas contained in said main tank, said liquefied gas being received in said first pipe at the receiving temperature,

step B of expanding said received gas to an expansion pressure less than the saturation vapor pressure of said received gas at said receiving temperature, so that part of said received gas evaporates due to the expansion effect and the remainder of said received gas remains liquid and cooled to a temperature less than the specified intake temperature, in particular because the specified intake gas is cooled to saturation temperature at the specified expansion pressure,

- step C filling said first drum with liquefied gas, and separating in said drum, in particular by gravity, said boil-off gas and said cooled liquefied gas,

step D of supplying said plant with at least a portion of said boil-off gas contained in said first drum, and

step E of cooling the liquefied gas contained in said main tank with the cooled liquefied gas contained in said first drum to cool the gas contained in said main tank.

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

According to the present invention, instead of using pressure reduction and cooling in the evaporation chamber and heat exchange between this evaporation chamber and the liquefied gas in the drum to cool the liquefied gas poured into the main tank, flash evaporation in the drum is used, and as a result, the cooled liquid medium is returned to the main tank. The advantage of this is primarily the suppression of the pinch effect in the heat exchange between the evaporation chamber and the liquefied gas from the drum.

According to one embodiment, the received liquefied gas consists of a pure gas, such as methane. In this case, the liquefied gas circulating in said first pipe may consist of a mixture including this pure gas, such as liquefied natural gas including methane.

The method according to the present invention may include one or more of the following steps or have one or more of the following features, either alone or in combination with each other:

step E includes pumping the cooled liquefied gas into said main tank by circulating it in said second pipe to cool the liquefied gas contained in said main tank;

- the method includes the step of spraying droplets of cooled liquefied gas into the gas contained in said main tank, which is above the level of liquefied gas contained in the main tank,

- the method includes the step of compressing the gas leaving the specified first outlet of the specified first drum;

- the pressure in the specified first drum is from 120 to 950 mbar abs. inclusive and/or the pressure in said main tank is between 20 and 700 mbarg. inclusive, from 20 to 350 mbar g. inclusive, or from 20 to 250 mbar g. inclusive, in particular for the tank at atmospheric pressure, and at pressures up to 10 mbar abs. for a pressure vessel, and/or the expansion results in the evaporation of a fraction from 0.94 to 15.18% inclusive, and/or the flow rate in the first pipe is from 18.09 to 374.7 t/h inclusive, and/or the production rate of cooled liquefied gas in the specified first drum is from 15.35 to 371.6 t/h inclusive, and/or the auxiliary tank has an internal volume or capacity from 1312 to 86037 m ³ inclusive, and/or the temperature of the cooled gas, after receiving the liquefied gas or natural stripping gas and cooling of this gas, is from -159 to -180.4 ° C inclusive, and / or the evaporation of compressed natural stripping gas leads to the evaporation of a fraction from 81.63 to 100% inclusive;

- the method includes the step of preheating the liquefied gas received in said main tank by heat exchange with the liquid medium circulating in said primary circuit after expansion and before pumping said liquefied gas, which can be partially or completely vaporized, into said first drum ;

- the method includes the step of pre-cooling the liquefied gas received in the specified main tank, by heat exchange with the liquid medium circulating in the specified secondary circuit, before pumping it into the specified auxiliary tank;

the method includes the step of cooling the gas leaving said first or second compressor by heat exchange with the cooled liquefied gas contained in said auxiliary tank;

the method includes the step of pre-cooling the gas leaving said first or second compressor before being cooled in said auxiliary tank by heat exchange with the stripping gas received in said main tank;

- the method includes the step of preheating the stripping gas received in said main tank before compressing it with said first or second compressor;

- the method includes the step of reducing the pressure and/or temperature of the gas intended to be supplied to the specified second drum, before filling the specified second drum;

- the method includes the step of pumping cooled liquefied gas into said main tank through said second pipe; this injection provides participation in the cooling of the liquefied gas contained in the main tank in order to limit the production of boil-off gas (BOG);

the method includes the step of transporting gas from said second drum to said second compressor; this gas can be used in the plant after compression.

The invention also relates to a method for supplying fuel gas to an energy production plant, in particular on board a ship, using the device described above, characterized in that it includes

step A of receiving the liquefied gas contained in said main tank, said liquefied gas being received in said first pipe at the receiving temperature,

step B of expanding said received gas to an expansion pressure less than the saturation vapor pressure of said received gas at said receiving temperature, so that part of said received gas evaporates due to the expansion effect and the remainder of said received gas remains liquid and is cooled to a temperature less than the specified intake temperature, in particular because the specified intake gas is cooled to saturation temperature at the specified expansion pressure,

- step C filling said first drum and separating in said drum, in particular by gravity, said liquefied gas and said refrigerated liquefied gas,

- the step F of supplying the refrigerated liquefied gas from said first drum to the auxiliary tank and storing the refrigerated liquefied gas in said auxiliary tank,

- step G of receiving the natural stripping gas in said main tank and preheating this gas,

step H of compressing both the stripping gas from said first drum and the preheated natural stripping gas,

- stage I of supplying said compressed gases to said plant.

The method according to the present invention may include one or more of the following steps or have one or more of the following features, existing alone 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 method includes the step of receiving cooled liquefied gas from said auxiliary tank and pumping this gas into said a main tank for cooling the liquefied gas contained in this main tank;

- the cooled liquefied gas is pumped directly into the liquefied gas and/or into the boil-off gas in the specified main tank.

The second object of the present invention relates to a device for cooling natural stripping gas for an energy production plant, in particular on board a ship,

characterized in that it includes

- an optional main tank for storing liquefied gas, including the first outlet for natural stripping gas,

- a means for receiving liquefied gas into the said main tank and cooling this liquefied gas,

- an auxiliary tank for refrigerated liquefied gas, configured to store liquefied gas cooled by said cooling means, and

- a first heat exchange circuit, including an inlet pipe connected to said first outlet pipe of said main tank for the purpose of circulating natural stripping gas in said circuit, wherein said first circuit is configured to communicate with said auxiliary tank so that said natural stripping gas passing through through said first circuit, cooled by liquefied gas cooled and stored in said auxiliary tank or coming from said auxiliary tank.

The main tank is optional in that it may or may not be considered an integral part of the device according to the invention. The device may, for example, be supplied without a main tank, which therefore does not form part of the device. Alternatively, after installation on a ship, for example, the device will be connected to the main tank, which thus forms part of the device in accordance with the present invention.

The solution thus offers an improvement in the management of boil-off gas (BOG) in a device adapted to the requirements of the ship, by cooling this boil-off gas (BOG), and provides the following possibilities:

- limiting the capacity of the medium used for refrigeration to the minimum required to control excess natural stripping gas (NBOG) instead of the minimum required to control maximum NBOG production,

- optimization of the degree of use of this means, which can be used continuously, and the source of cold, such as refrigerated liquefied gas, can be stored if necessary,

- Ensuring that the cooling capacity produced is used properly when needed.

The solution is adapted to any type of medium that is used to cool a liquid medium. In this case, the liquid medium is boil-off gas (BOG) coming from the tank, cooling in the auxiliary tank and finally returning to the tank where it will be cooled.

The device according to the present invention may have one or more of the following features, either alone or in combination with each other:

- the first separation drum, the inlet pipe of which is connected to the outlet pipe of the specified first circuit for supplying to the specified first drum the cooled natural stripping gas and the recondensed natural stripping gas forming the cooled liquefied gas, while the first drum includes the first outlet pipe natural stripping gas and a second refrigerated liquefied gas outlet connected to said main tank for pumping refrigerated liquefied gas into said main tank;

- the specified second tank is configured to store the cooled liquefied gas at a pressure greater than the operating pressure of the specified first drum;

- the device includes at least one first compressor, the inlet pipe of which is connected to the specified first outlet pipe of the natural stripping gas from the specified main tank and/or with the specified first outlet pipe of the natural stripping gas from the specified first drum;

- said cooling means includes a second heat exchange circuit which is designed to exchange heat with the liquefied gas in said auxiliary tank or coming from said auxiliary tank, and in which the cooling liquid medium is circulated to cool said liquefied gas so that the cooled liquefied gas is produced directly in said auxiliary tank, and for the production of refrigerated liquefied gas;

- said cooling means includes

♣ a second drum, the inlet of which is connected to the first end of the first pipe, the second end of which is immersed in the liquefied gas contained in the specified main tank, and the specified first pipe is configured to supply the said second liquefied gas drum, and also

♣ a second pipe, the first end of which is connected to the first outlet of the refrigerated liquefied gas of the specified second drum, and the second end of which is connected to the specified auxiliary tank for supplying the specified auxiliary tank of the refrigerated liquefied gas;

said second drum is a separation drum and/or an expansion drum;

- the device includes a first heat exchanger, the primary circuit of which has an inlet pipe connected to the outlet pipe of the liquefied gas of the specified main tank, and the secondary circuit has an inlet pipe connected to the specified first pipe, and an outlet pipe connected to the inlet pipe of the specified second drum;

said second heat exchanger is not immersed in liquefied gas in said main tank and is not installed in the main tank;

- the outlet pipe of the primary circuit of the specified second heat exchanger is connected to the inlet pipe of the specified auxiliary tank to supply the specified auxiliary tank of the refrigerated liquefied gas;

- the device does not contain any 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 the outlet of a third pump intended to be immersed in liquefied gas in said main tank;

- the device includes

♣ a first pump connected to said second end of said first pipe and designed to be immersed in said liquefied gas contained in said main tank so as to circulate the liquefied gas through said first pipe from said main tank to said second drum, and

♣ a second pump connected to said second pipe so as to circulate cooled liquefied gas from said second drum to said auxiliary tank.

- the specified first pipe includes the specified means of evaporation;

- the device includes at least one second compressor, the inlet pipe of which is connected to the specified first outlet pipe of the stripping gas of the specified main tank;

- the specified second compressor contains an outlet pipe connected to the specified inlet pipe of the specified primary circuit;

said inlet of said second compressor is further connected to a second gas outlet of said second drum and/or to a second gas outlet of said first drum;

- the specified inlet pipe of the specified second compressor is connected to the outlet pipe of the specified first compressor;

- the specified first or second compressor includes an outlet pipe made with the possibility of supplying fuel gas, in particular, in the specified installation;

- said inlet of said first circuit is connected to said outlet of said first or second compressor via a primary circuit of a second heat exchanger, said second heat exchanger comprising a secondary circuit whose inlet is connected to said first outlet of natural stripping gas from said main tank, and an outlet the branch pipe of which is connected to the inlet pipe of the specified first or second compressor;

Said auxiliary tank is connected to a first end of a third refrigerated liquefied gas pipe, the second end of which is intended to be connected to said main tank, said third pipe being configured to transport at least a portion of said refrigerated liquefied gas from said auxiliary tank to said main tank;

said third pipe includes a dip pipe for immersion in the liquefied gas contained in said main tank and/or a spray manifold in said main tank for pumping cooled liquefied gas into said main tank;

- said inlet of said first circuit is connected to said outlet of at least one compressor, for example the first or second said compressor, by means of a primary circuit of a second heat exchanger, said second heat exchanger including a secondary circuit whose inlet is connected to said outlet natural stripping gas from the specified main tank, and the outlet of which is connected to the inlet of the specified first or second compressor; heat exchange therefore takes place in advance (heat exchange must take place in advance, since the flash gas is less cold than the cooled liquefied gas) between the entire volume of flash gas (including the part fed to the plant) and the compressed part of this flash gas (excess from plant consumption that is re-condensed);

- the device does not contain any components other than pumps and / or pipes immersed in liquefied natural gas contained in the specified main tank.

The benefits and advantages described above in connection with the features of the device according to the first aspect of the present invention naturally apply to the same features of the device according to the second aspect, and vice versa.

The present invention also relates to ships, in particular for the transport of liquefied gas, and includes at least one device as described above.

The method according to the present invention may include one or more of the following steps and have one or more of the following features, existing alone or in combination with each other:

- the method includes

♣ the step of compressing gas from said first outlet of said main tank, and/or

♣ the step of compressing gas from said second outlet of said first drum, and/or

♣ the step of compressing gas from said second outlet of said second drum;

- the method includes the step of pre-cooling the compressed gas before it is cooled in said auxiliary tank by heat exchange with natural stripping gas received in said main tank and circulating in said secondary circuit of said second heat exchanger;

the method includes the step of preheating the stripping gas received in said main tank by heat exchange with a liquid medium circulating in said primary circuit of said second heat exchanger before compressing the gas;

- the method includes the step of cooling the liquefied gas contained in said auxiliary tank;

- the method includes the step of expanding the liquefied gas in such a way that part of said gas evaporates due to the expansion effect, and the rest of said gas remains in a liquid state and cools;

- the method includes the step of filling said second drum and separating in said first drum, in particular by gravity, said vaporized gas from said cooled liquefied gas;

- the method includes the step of supplying said auxiliary tank with refrigerated liquefied gas;

- the method includes the step of preheating the liquefied gas received in said main tank by heat exchange with a liquid medium circulating in said primary circuit of said first heat exchanger after expansion and before pumping said liquefied gas into said second drum;

- the method includes the step of cooling the liquefied gas received in said main tank by heat exchange with a liquid medium circulating in said secondary circuit of said first heat exchanger before pumping it into said auxiliary tank.

The benefits and advantages described above in connection with the features and steps of the method according to the first aspect of the present invention naturally apply to the same features and steps of the method according to the second aspect, and vice versa.

The invention also relates to a method for cooling a liquefied gas and/or an liquefied gas from the evaporation of an liquefied gas for an energy production plant, in particular on board a ship, using the apparatus described above, characterized in that it comprises

- stage A of the preparation of refrigerated liquefied gas in the specified auxiliary tank,

- stage B of receiving refrigerated liquefied gas in the specified auxiliary tank,

- step C of pumping said refrigerated liquefied gas into said boil-off gas and/or said liquefied gas contained in the main tank.

The invention also relates to a method for supplying fuel gas to an energy production plant, in particular on board a ship, using the apparatus described above, characterized in that it comprises monitoring at least one gas consumption parameter of said plant, and

- if the value of the specified parameter is higher than the specified threshold value, the stage of preparation and storage of the refrigerated liquefied gas, in particular in the specified auxiliary tank,

if the value of the specified parameter is below the specified threshold value, the step of re-condensing the natural stripping gas produced in excess in the specified main tank.

The method may include the step of cooling the gas contained in said main tank using said refrigerated liquefied gas in order to limit the production of stripping gas.

The predetermined threshold may change, for example, during a ship's voyage. From a functional point of view, this threshold value can correspond to the volume of natural stripping gas (NBOG) that must be removed from the main tank in order to eliminate the need to control the pressure in the latter.

Preferably, the refrigerated liquefied gas is prepared if the production of stripped gas is not sufficient to meet the gas demand of said plant.

The liquefied gas is preferably cooled by receiving, expanding and separating the phases of the liquefied gas contained in said main tank.

Natural stripping can be retarded in a number of ways: by pumping cooled LPG into a tank car (e.g. via a manifold to spray cooled LPG into a tank car, or by simply pumping it into a main tank), or by exchanging cold (i.e. using a heat exchanger) between the gas natural stripping and cooled gas, which allows the re-condensation of natural stripping gas (possibly with a return to the tank).

The fact that the liquefied gas is supercooled makes it possible not to create boil-off gas if natural stripping is to be slowed down. Storage allows high recondensation requirements to be reduced by means of an auxiliary tank of limited capacity, without the use of a very costly liquefaction unit, the cost of which depends on its capacity.

Alternatively, the cooled gas is stored in the main tank to condense the stripping gas in this tank, in particular if the available amount of stripping gas in this tank exceeds the needs of the plant. The cooled gas has a higher density than the rest of the gas in the main tank, so it is necessary, for example, to cool/recondense the natural stripping gas from the liquefied gas at the bottom of the main tank, for example, below the liquid outlet or heat exchanger. A heat exchanger may be provided at this location, for example, or a pipe designed to feed the stored cooled gas at this location to a heat exchanger (located, for example, outside the tank) with the stripping gas.

This is an advantage if

- said stripping gas is condensed by heat exchange with said refrigerated liquefied gas, and/or

said stripping gas is compressed prior to said heat exchange, and/or

- said stripping gas undergoes depressurization after said heat exchange, and/or

said stripping gas undergoes phase separation after said depressurization.

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

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood and other details, features and advantages of the present invention will become more apparent upon reading the following description, given by way of non-limiting example and with reference to the accompanying drawings, in which:

- figure 1 is a schematic representation of the device in accordance with the first embodiment of the present invention, on which the device is installed on a ship,

- fig. 2 to 6 are schematic representations corresponding to FIG. 1 illustrating the steps of the method according to the invention,

- fig. 7 is a schematic representation of a device according to the second embodiment of the present invention, on which the device is installed on a ship,

- fig. 8 is a schematic representation of a device according to the third embodiment of the present invention, on which the device is installed on a ship,

- fig. 9 and 10 are schematic representations of a device according to a fourth embodiment of the present invention, on which the device is installed on a ship, illustrating the steps of the method according to the invention,

- fig. 11 is a schematic representation of a device according to the fifth embodiment of the present invention, on which the device is installed on a ship,

- fig. 12 is a schematic view of a device according to a sixth embodiment of the present invention, on which the device is installed on a ship,

- fig. 13 is a schematic view of a device according to a seventh embodiment of the present invention, on which the device is installed on a ship.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 shows an apparatus 10 according to a first embodiment of the present invention for refrigeration of liquefied gas and/or refrigeration of natural stripping gas from liquefied gas.

The device 10 is particularly, but not exclusively, suitable for supplying fuel gas to a ship, such as an LPG ship. The device 10 can thus be used to supply fuel gas to a power generation plant 12, in particular on board a ship.

The vessel includes a tank 14 or a plurality of tanks 14 for storing liquefied gas. The gas is, for example, methane or a gas mixture containing methane. This tank 14 or each of the tanks 14 may contain the gas in liquefied form at a given pressure and a given 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 through the device 10 according to the invention. Thus, the number of tanks does not limit the invention. It is, for example, a number from 1 to 6. The capacity of each tank 14 can be from 1000 to 50,000 m ³ .

In the following, the term "tank" should be interpreted as "this or each tank".

Tank car 14 contains liquefied gas 14a and gas 14b resulting from stripping, in particular natural stripping, of liquefied gas 14a in tank 14. The liquefied gas 14a is naturally stored at the bottom of tank 14, while the boil-off gas 14b is located above the gas in a tank, represented schematically by the letter N.

Hereinafter, "LNG" means liquefied gas, i.e. gas in liquid form, "BOG" means boil-off gas, "NBOG" means natural stripping gas, and "FBOG" means forced stripping gas. These abbreviations are known to those skilled in the art as they correspond to the first letters of the corresponding English words.

In the embodiment shown in FIG. 1, pumps 16a, 16b are immersed in LNG in tank 14 and are preferably located at the bottom of the tank to ensure that only LNG is supplied to them.

Here are two pumps 16a, 16b. Pump 16a is connected to one end, here the lower end, of pipe 18. Pump 16b is connected to one end, here the lower end, of pipe 20. Alternatively, more pumps of each type may be provided, for example, to provide redundancy for pumps 16a and 16b, or to use existing pumps, for example spray pumps already present on the ship (in this case the function of pump 16b could be performed by four spray pumps, each present in one of the four separate tanks).

The upper end of the pipe 20 is connected to an LNG droplet spray manifold 22 located at the top of the tank 14 above level N. The manifold 22 is thus configured to spray the LNG droplets into the NBOG. This allows forced recondensation of the NBOG in the tank 14. The pump 16b is configured to circulate the LNG in the pipe 20 from the bottom of the tank 14 to the manifold 22 and spray the LNG in droplets. In practice, a gaseous atmosphere may be present in the main tank while NBOG may be circulating in the pipes.

Pump 16a is configured to circulate LNG in pipe 18 from the bottom of tank 14 to a drum 24 connected to one end, such as the top end, of pipe 18. Pipe 18 includes pressure reducing means 19, such as a throttle valve to reduce pressure. LNG circulating in pipe 18 before reaching drum 24. Means 19 are preferably configured such that the pressure of LNG circulating in pipe 18 is reduced to the operating pressure of drum 24. Means 19 includes, for example, a throttle valve (as described below) .

The circulation of the LNG in the pipe 18 and through the pressure reducing means 19 thus leads to at least partial evaporation of the LNG before being fed into the drum 24.

Drum 24 is thus designed to receive partially vaporized LNG coming from tank 14. The operating pressure inside drum 24 is less than the pressure at which LNG is stored in tank 14. Feeding LNG into drum 24 may result in additional LNG vaporization, which is reflected , on the one hand, in the production of FBOG in drum 24 and the cooling of the LNG remaining in the drum, which is called "cooled liquefied gas". The drum 24 contains gas in liquefied form at a given pressure and a given temperature.

The drum 24 therefore contains the cooled liquefied gas 24a and the vaporized gas 24b, i. forced stripping of liquefied gas 14a coming from tank 14. Cooled liquefied gas (LNGs) 24a is stored at the bottom of drum 24, and boil-off gas (or FBOG) 24b is located below the level of liquefied gas in drum 24, schematically represented by the letter L.

The drum 24 has three fluid transfer ports, namely an inlet LNG connected to pipe 18, an outlet FBOG, and an outlet LNGs.

The FBOG outlet is connected to an inlet of a compressor 26 whose outlet is connected to a compressor 28. Compressors 26, 28 may be two independent compressors or two compression stages of the same compressor. The compressors 26, 28 can therefore be combined.

Here, the compressor 26 is used to generate operating pressure inside the drum 24. Therefore, it is configured to reduce the pressure in the drum 24 in relation to the tank 14. The pressure difference between them may be sufficient to force the circulation of LNG from the tank to the drum 24. In this case, it is clear that that pump 16a is optional. The conditions created in the drum 24 by the compressor 26 are designed to produce LNGs in the expansion drum.

If the number of LNGs in drum 24 is too high and there is a risk of reaching a threshold level, the LNGs can be pumped from the LNGs outlet of the drum 24 to the LNGs inlet of the auxiliary tank 30.

Here, drum 24 and auxiliary tank 30 are connected by pipe 31 including, for example, valve 33 and pump 35. Pump 35 is configured to circulate LNGs from drum 24 to auxiliary tank 30. Pump 35 is particularly useful when tank 30 is at more than higher pressure than drum 24. Auxiliary tank 30 contains LNGs at a given pressure and a given temperature.

Auxiliary tank 30 is configured to store excess LNGs produced in drum 24. Tank 30 therefore contains refrigerated liquefied gas 30a and gas 30b resulting from the evaporation, in this case natural stripping, of liquefied gas 14a coming from tank 14. Refrigerated liquefied gas (or LNGs) 30a is stored at the bottom of the auxiliary tank 30, while the boil-off gas 30b is located above the level of liquefied gas in this tank, schematically represented by the letter M.

Auxiliary tank 30 has an outlet LNGs. In the example shown, the outlet is connected by a pipe 32, on the one hand, to the spray manifold 22 of the tank 14 or each of the tanks 14, and on the other hand, to a dip pipe 34 intended to be immersed in the LNG in the tank. Thus, it is clear that LNGs can be supplied to the spray manifold 22 to spray droplets of LNGs into the BOG in tank 14 and LNGs can be supplied to dip tube 34 to pump the LNGs directly to the LNG in tank 14.

The pipe 32 may be connected to the LNGs outlet of the auxiliary tank 30 via a valve 36. The pipe may be connected to the dip pipe 34 and manifold 22 via a three-way valve 38.

Here, the auxiliary tank 30 is used to cool a fluid such as a gas or liquid, which in this case is the BOG from the main tank 14. Here, the heat exchanger circuit 40 is connected to the auxiliary tank 30. Here, the term "connected" should be understood in a broad sense, since loop 40 may be, for example, a coil immersed in LNGs contained in auxiliary tank 30. Loop 40 may alternatively be located outside tank 30. Loop 40 is designed such that heat exchange occurs between the liquid medium circulating in loop 40 and LNGs contained in auxiliary tank 30. The fluid circulating in loop 40 is generally hotter than the LNGs, which therefore cools the fluid when it is not circulating in loop 40. The loop has an inlet and outlet.

The inlet of the circuit 40 is connected to the outlet 45 BOG of the main tank 14, which is here at the upper end of the tank. The BOG outlet 45 of the tank 14 is connected to the inlet of the secondary circuit 42a of the heat exchanger 42, the outlet of which is connected to the inlet or inlet of the compressor 28.

The compressor outlet 28 is generally connected to the plant 12 to supply it with fuel gas. A portion of the fuel gas exiting compressor 28 may be received and redirected through pipe 44, which may be connected to the compressor outlet 28 via a three-way valve 46.

Compressor 28 is configured to compress gas (eg, NBOG from a tank car) to an operating pressure suitable for its use in plant 12.

Pipe 44 is connected to the inlet of the primary circuit 42b of the heat exchanger 42, the outlet of which is connected to the inlet of the circuit 40.

The outlet of circuit 40 is connected via pipe 48 to drum 50 separated from drum 24. Pipe 48 includes a valve 52, which is preferably a Joule-Thomson valve, to lower the temperature of the gas by adiabatic expansion.

Joule-Thomson expansion is slow, stationary laminar expansion, which is caused by the passage of a gas flow through a plug (usually made of cotton wool or raw silk) into a thermally insulated and horizontal pipe, and the pressure to the left and right of the plug is different. For real gases, the Joule-Thomson expansion is usually accompanied by a change in temperature: this is the Joule-Thomson effect. Heat exchanger 42, loop 40 and valve 52 cool and partially (re)condense the BOG.

The drum 50 is designed to separate the BOG 50b that remains in gaseous form from the (re)condensed BOG 50a before being fed into the (re)condensed BOG tank 14. The recondensed BOG 50a is naturally stored at the bottom of the drum 50 and the boil off gas (or BOG) 50b is located below the liquid gas level in the drum 50, represented schematically by the letter O.

Drum 50 includes three fluid transfer conduits, namely a BOG inlet connected to conduit 48, a gaseous BOG outlet, and a (re)condensed BOG outlet. Here, the gaseous BOG outlet is connected to the compressor inlet 28. Here, the (re)condensed BOG outlet is connected to dip pipe 34, pipe 32 and/or spray manifold 22 to pump the (re)condensed BOG to tank 14.

The vacuum evaporation means formed by the pump 16a, the pressure reducing means 19, the drum 24 and the compressor 26 make it possible to use the latent heat of evaporation, which is generally spent in the prior art to produce FBOG and the cooling power, which is used in particular to cool the LNG contained in the main tank 14.

The LNGs generate cooling capacity that can be stored in the auxiliary tank 30 when it is not required, for example during phases in which the amount of NBOG produced is insufficient to meet demand.

The latent heat of vaporization is exploited by the device 10 described above, and in particular by the drum 24, whose operating pressure is lower than that of the tank 14, which is, for example, between -20 and 250 mbarg. inclusive (overpressure) (either -20 to 350 mbarg or -20 to 700 mbarg). The operating pressure of drum 24 is preferably between 300 and 800 mbar abs. (absolute pressure) inclusive.

LNG coming from tank 14 at saturation equilibrium corresponding to the pressure at which LNG is stored in tank 14 is directed to drum 24, which is at a lower pressure than tank 14. Therefore, this LNG is in a superheated state and when its pressure is reduced by means 19, to reach saturation equilibrium, it releases excess heat by evaporation. The LNG is then separated into LNGs and FBOG within drum 24 in proportions that depend in part on the operating pressure of drum 24.

For example, at an operating pressure of 300 mbar abs. the amount of evaporation of LNG supplied to the drum 24 is in the range from 9.5 to 10% inclusive. At 800 mbar abs., this volume is between 2.3 and 3% inclusive. The remainder is a liquid cooled to a temperature corresponding to the saturation equilibrium at the operating pressure of the drum 24. For example, at an operating pressure of 300 mbar abs. LNG is cooled to a temperature of -172 to -175 °C (temperature drop from -12 to -15 °C), and at 800 mbar abs. LNG is cooled down to -163 to -164°C (temperature drop from -3 to -4°C).

The LNGs may then be pumped out via pump 35, preferably to an auxiliary tank 30. Pump 35 may be used to pressurize the LNGs. Storing the LNGs in the auxiliary tank 30 allows the calorific value to be retained.

During operation, the evaporating part of the LNG supplied to the drum 24 will accumulate in this drum. To bring the pressure in drum 24 to a predetermined value (eg, 300 to 800 mbar abs.), the FBOG produced in drum 24 is preferably continuously withdrawn. This is done by a compressor 26 which is configured to draw in the gas contained in the drum 24 with an inlet pressure corresponding to the operating pressure of the drum 24 and an outlet pressure which, for example, corresponds to the pressure at which the LNG is stored in the tank 14. The gas treated in this way is then easy to use because it is at a pressure similar to that of the NBOG produced in tank car 14 and the NBOG can be fed to the same compressor 28. This compressor 28 is configured to produce fuel gas directly used in installation 12, for example, to power the ship's propulsion system.

With the help of the device 10 described above, for gas consumption by the plant 12, the NBOG produced in the tank 14 is sent to the compressor 28, which compresses it to the required pressure. The additional BOG required to meet demand is produced by forced evaporation of the LNG supplied to drum 24 and then applied in series to compressors 26 and 28. Pump 16a may be necessary to supply LNG from tank 14 to drum 24, particularly if the tank or the N level is from 10 to 50 m inclusive - in this case, the pressure reduction in the drum 24 by itself may not be sufficient for the passive circulation of LNG in the pipe 18.

Therefore, enough LNG must be supplied to drum 24 to meet the fuel gas requirement of plant 12 in combination with NBOG. Therefore, depending on the composition of the LNG and the operating pressure of the drum 24, the flow from the tank 14 to the drum 24 can be in the range from 0 to 17.5 t/h inclusive.

The LNGs produced in the drum 24 are stored in the auxiliary tank 30. The tank 30 is configured to store and store the LNGs, and therefore should preferably be thermally insulated. The pressure in the auxiliary tank 30, for example, is between 0.3 and 10 bar abs. inclusive to provide flexibility in pressure control. The temperature of the LNGs in the tank 30 is close to the temperature of the LNGs in the drum 24, and is, for example, from -175 to -161 °C inclusive. If necessary, for example, during phases with excess NBOG, the LNGs contained in the auxiliary tank 30 can be directed in the pipe 32 to the frame 22 with nozzles to spray droplets of LNGs into the BOG contained in the tank 14 and thus to cool the BOG . It can also be pumped through the dip tube 34 into the LNG in the tank car to cool the LNG directly.

The excess NBOG produced in relation to plant 12's needs is pumped out and sent to compressor 28. It is then redirected through valve 46 to auxiliary tank 30 loop 40 where it is cooled by heat exchange with previously stored LNGs as explained above. Excess NBOG is then directed to valve 52 whereby its pressure is reduced to a pressure close to the storage pressure in tank 14. For example, if the tank is an atmospheric pressure tank, the excess NBOG can be depressurized to between 0 and 1 bar. The excess NBOG then enters drum 50 where it undergoes phase separation into (re)condensed BOG and gaseous BOG. Gaseous BOG is sent through pipe 51 to compressor 28 under the same conditions as NBOG, which is produced in tank 14. As for the (re)condensed BOG, it is pumped into tank 14 for LNG storage.

In FIG. 2 - 6 show the stages of operation of the device according to figure 1, which may correspond to the stages of operation of a vessel equipped with this device.

The liquefied gas cooling process is described here in three steps:

1. Stage where the amount of NBOG is insufficient, also called the FBOG stage (figs. 2 and 3), for example, if the ship is sailing at a speed that requires more BOG added to the NBOG produced in the tank or tanks 14. Additional BOG or FBOG will be supplied by the device 10 and a cooling capacity will be generated.

2. The stage in which excess NBOG is produced (figs. 4 and 5), for example, if the ship is sailing at low speed or at anchor, the excess NBOG must be disposed of in a safe and environmentally friendly way.

3. The stage in which the ship's main tank 14 is cooled (FIG. 6), for example, before loading after a return trip (during which BOG control is generally not necessary, since the tank or tanks 14 are practically empty).

1. Stage where the amount of NBOG is insufficient, also called the FBOG stage (Fig. 2 and 3)

In FIG. 2 shows the steps of the first stage, in which FBOG and LNGs are produced together by the device.

To control the pressure in tank 14, NBOG is pumped out of this tank through outlet 45 and then fed to compressor 28, which will produce fuel gas at a pressure suitable for unit 12, for example, on the order of 6-7 bar, 15-17 bar or 300 -315 bar. In order to replenish the amount of gas and to meet the needs of plant 12, the LNG from the tank 14 is sent by means of a pump 16a and a pipe 18 to a pressure reduction means 19, in which the pressure of the LNG is reduced to the operating pressure of the drum 24. The LNG reaches the drum 24 at the operating pressure of this drum and , due to the displacement of the saturation equilibrium caused by pressure differences between the drum 24 and the tank 14, part of the LNG evaporates (this is an instantaneous phenomenon) between the pressure reducing means 19 and the drum, and the rest is cooled to the saturation temperature of the LNG at the operating pressure of the drum. Sufficient volume must be taken from tank 14 as explained above. The FBOG contained in drum 24 is then pumped out and compressed by compressor 26 to the pressure at which the LNG is stored in tank 14. The FBOG is then compressed again by compressor 28 to the pressure required for installation 12. In order not to overfill drum 24, LNGs from this drum is sent to the auxiliary tank 30, in particular, if the fill level of the drum LNGs reaches a certain threshold level, for example, 50%.

In FIG. 3 shows the other steps of the first stage, in which LNGs are stored in the auxiliary tank 30.

If the capacity of the auxiliary tank 30 is not sufficient to store the produced LNGs, then the LNGs contained in the tank 30 can be pumped to the bottom of the tank 14 through the pipe 32 and dip tube 34 to cool the LNG in the tank 14 to a temperature below the saturation temperature of the LNG at pressure tank storage 14.

2. Stage at which an excess of NBOG is produced (numbers 4 and 5)

In FIG. 4 shows the second step steps in which excess BOG is recondensed.

The NBOG produced in tank car 14 is produced in sufficient or more than sufficient quantities to meet the gas demand of plant 12. To regulate the pressure in tank car 14, BOG is pumped out of this tank and fed to compressor 28 to achieve the pressure required for plant 12. Excess BOG , which cannot be consumed by the plant, is directed from the compressor outlet 28 to the heat exchanger 42, where it is cooled by heat exchange with cold NBOG taken directly from the tank 14 through the outlet 45. The excess BOG is then sent to the circuit 40 of the auxiliary tank 30, where it is cooled again by heat exchange with the LNGs stored in this tank, as explained above. Excess BOG is then depressurized by valve 52 and fed to bowl 50 where BOG is (re)condensed by heat exchanger 42, loop 40 and valve 52 and separated from gaseous BOG. The remaining gaseous BOG is returned to compressor 28 to be fed to unit 12.

In FIG. 5 shows the second step steps in which the LNGs are sprayed.

Instead of recondensing excess NBOG via a dedicated line, it is possible to transfer the LNGs contained in auxiliary tank 30 to pipe 32 and then to spray manifold 22 to directly recondense the BOG contained in tank 14.

3. The stage at which the main tank of the ship is cooled (Fig. 6)

In FIG. 6 shows the steps of the final stage.

In reliquefaction terminals where a ship is loading its cargo, a low temperature in tank 14 is generally required before loading to limit the amount of LNG that will be flashed ( flashing ). Typically this is achieved by using manifold 22 and associated LNG spray pump 16b already contained in tank 14 to cool the BOG in that tank. Thanks to the device 10, this operation can be carried out by supplying the collector 22 with LNGs from the auxiliary tank 30 and therefore a colder gas than the LNG contained in the tank 14. In the same way, if the amount of BOG contained in the tank 14 is not is sufficient to supply plant 12, the LNGs contained in the auxiliary tank 30 can be produced in the same manner as during the first stage.

FIG. 7 is an embodiment of the device which differs from that shown in FIG. 1 in that it includes another heat exchanger 60. Heat exchanger 60 includes two circuits, namely a primary circuit 60a and a secondary circuit 60b.

The secondary circuit 60b has an inlet connected to the pipe 18, in this case located downstream of the means 19 pressure reduction. The secondary circuit 60b has an outlet connected to the inlet LNG of the drum 24.

The primary circuit 60a has an inlet pipe connected via a three-way valve 62 to the pump 16b and to the spray manifold 22 of the tank 14, respectively. The primary circuit 60a has an outlet pipe connected to the inlet pipe LNG of the auxiliary tank 30.

Secondary circuit 60b is a cold circuit. The liquid medium circulating in this circuit, and in this case the reduced pressure LNG, is intended to be heated by circulation in this circuit in order to evaporate it (resulting in the production of FBOG). Primary circuit 60a is the hot circuit. The liquid medium circulating in this circuit, and in this case the LNG from tank 14, is intended to be cooled by circulating in this circuit. However, circuit 60a is not suitable for evaporating heavier components (ethane, propane, etc.). Obviously, the reduction in pressure upstream of the secondary circuit 60b provides a reduction in the evaporation temperature, which allows the production of FBOG by heat exchange with the LNG received from the tank and circulating in the primary circuit. The evaporation that produces FBOG requires the input of heat provided by the LNG circulating in the primary circuit, and this is therefore a source of cold for cooling the LNG circulating in the primary circuit.

The LNG from the tank 14 is thus conveyed by pump 16a to the pressure reducing means 19 and then circulated in the secondary or cold circuit of the heat exchanger 60. During the break, the LNG from the tank is conveyed by the pump 16b to the primary or hot circuit of the heat exchanger 60. Therefore, the heat exchange between these circuits leads to the following:

- heating the depressurized and partially vaporized LNG to continue its evaporation, after which it is sent to the drum for phase separation,

- cooling LNG, which is fed into the auxiliary tank 30 for storage in it for later use.

Thereafter, the device operates as originally described with reference to Figures 1-6. Here, the effect of the heat exchanger 60 is as follows:

- pump 16a may be sized to cause only a predetermined maximum amount of LNG to circulate to generate enough FBOG to meet the demand of plant 12, in addition to NBOG. This task can be carried out using the fuel pump, which is usually installed on the boat,

- the capacity of the drum 24 can be reduced, since the flow rate of the supplied LNG can be lower (only the additional volume of FBOG will be used to meet the demand for fuel gas of the plant 12),

- due to the pinch effect of the temperature in the heat exchanger, the production of cooling power is reduced (loss of approx. 15% at an operating pressure of 500 mbar abs.),

- consumption of LNG and circulating LNGs is reduced thanks to this solution; consequently, the energy consumption of the pumps is reduced, which reduces the energy consumption of the entire system.

In FIG. 8 shows another embodiment of an apparatus 110 according to the invention in which liquefied gas cooling and/or liquefied gas stripping gas cooling is performed.

The device 110 is adapted, in particular, but not exclusively, for the supply of fuel gas to a ship, for example, a ship for the transport of liquefied gas. The device can thus be used to supply fuel gas to a power generation unit 112 on board a ship.

The vessel includes a tank 114 or a plurality of tanks 114 for storing liquefied gas. The gas is, for example, methane or a mixture of gases including methane, such as liquefied natural gas. This tank 114, or each of the tanks 114, may contain the gas in liquefied form at a given pressure and a given temperature, such as atmospheric pressure and a temperature in the order of -160°C. One or more tanks 114 of the ship can be connected to the installation 112 through the device 110 in accordance with the present invention. Thus, the number of tanks does not limit the invention. It is, for example, a number from 1 to 6 inclusive. The capacity of each tank 114 can be from 1000 to 50,000 m ³ inclusive.

In the following, the term "tank" should be interpreted as "this or each tank".

Tank car 114 contains liquefied gas 114a and gas 114b resulting from the stripping, in particular natural stripping, of liquefied gas 114a in tank 114. The liquefied gas 114a is naturally stored in the lower part of the tank 114, while the boil-off gas 114b is located above the level of the liquefied gas. gas in a tank, represented schematically by the letter N.

Hereinafter, "LNG" means liquefied gas, i.e. gas in liquid form, "BOG" means boil-off gas, "NBOG" means natural stripping gas, and "FBOG" means forced stripping gas. These abbreviations are known to those skilled in the art as they correspond to the first letters of the corresponding English words.

In the embodiment of the invention shown in FIG. 8, the tank 114 includes a manifold for spraying LNG droplets 122, which is located at the top of the tank, above level N. The manifold 122 is thus configured to spray LNG droplets into the BOG. This makes it possible to force the BOG to recondense in tank 14.

Here, the apparatus 110 includes a cooling means 170 that is associated with an auxiliary tank 130 for storing LNGs.

Cooling means 170 includes, for example, a heat exchange circuit 172 associated with tank 130. Auxiliary tank 130 contains LNGs at a given pressure and a given temperature.

Auxiliary tank 130 is configured to store LNGs. The tank 130 therefore contains the refrigerated liquefied gas 130a and the gas 130b resulting from the evaporation of the liquefied gas 130a. Refrigerated liquefied gas (LNGs) 130a is naturally stored in the lower part of the auxiliary tank 130, while the boil-off gas 130b is located above the level of liquefied gas, schematically represented by the letter M.

Auxiliary tank 130 contains the outlet of the LNGs. In the example shown, the outlet is connected by a pipe 132, on the one hand, to the spray manifold 122 of the tank 114 or each tank 114, and on the other hand, to a dip pipe 134 designed to be immersed in the LNG in the tank 114. Thus, it is clear that LNGs can be fed into the spray manifold 122 to spray droplets of LNGs into the boil-off gas (BOG) in tank 114 and the LNGs can be fed into dip tube 134 to pump the LNGs directly to the LNG in tank 114.

Pipe 132 may be connected to the LNGs outlet of auxiliary tank 130 via valve 136. Pipe may be connected to dip pipe 134 and manifold 122 via three-way valve 138.

Here, the auxiliary tank 130 is used to cool a fluid such as a gas or liquid, which in this case is the BOG from the main tank 114. Here, another heat exchanger circuit 140 is connected to the auxiliary tank 130. Here, the connection of each circuit 140, 172 with the auxiliary tank 130 should be understood in a broad sense, since the circuits 172 and 140 may be, for example, coils immersed in LNGs contained in the auxiliary tank 130. These circuits may alternatively be located outside the tank 130. The circuit 140 is designed in such a way that heat exchange occurs between the liquid medium circulating in the loop and the LNGs contained in the auxiliary tank 130. The liquid medium circulating in the loop 140 is generally hotter than the LNGs, which therefore cools the liquid medium as it circulates in the loop 140. The loop has inlet and outlet pipes.

The inlet of the circuit 140 is connected to the outlet 145 BOG of the main tank 114, which is here at the upper end of the tank. BOG outlet 145 from tank 140 is connected to secondary circuit inlet 142a of heat exchanger 142, whose outlet is connected to compressor inlet 128.

Compressor outlet 128 is generally connected to unit 112 to supply it with fuel gas. A portion of the fuel gas exiting compressor 128 may be received and redirected through pipe 144, which may be connected to compressor outlet 128 via three-way valve 146.

Compressor 128 is configured to compress the gas to an operating pressure suitable for use in plant 112.

Pipe 140 is connected to the inlet of the primary circuit 142b of the heat exchanger 142, the outlet of which is connected to the inlet of the circuit 140.

The outlet of the circuit 140 is connected through a pipe 148 to the drum 150. The pipe 148 includes a valve 152, such as a Joule-Thomson valve, to reduce the temperature of the gas by adiabatic expansion.

Heat exchanger 142, circuit 140 and valve 152 condense (in other words, (re)liquefy) some of the (BOG).

The drum 150 is designed to separate the (re)condensed BOG from the BOG remaining as a gas.

Drum 150 therefore contains BOG 150a, (re)condensed (via a condenser line including, for example, heat exchanger 142, loop 140 and valve 152), and gaseous BOG 150b. Condensed BOG 150a is stored at the bottom of drum 150 and gaseous BOG 150b is located above the liquid gas level in drum 150, represented schematically as O.

Drum 150 has three fluid transfer ports, namely a BOG inlet connected to pipe 148, a gaseous BOG outlet, and a liquid BOG outlet. Here, the condensed BOG outlet is connected to the compressor inlet 126 by pipe 151. Here, the liquid BOG outlet is connected to dip pipe 134, pipe 132, and/or spray manifold 122 for storing LNG in tank 114.

Fig. 9 is an embodiment of device 110 that differs from that shown in FIG. 8 by cooling means 170.

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

The pump 116a is connected to one end, here the lower end, of the pipe 118. The pipe 118 has an upper end connected to the LNGs inlet of the auxiliary tank 130 for supplying LNGs to that tank. Conduit 118 extends through or includes a cold generator, such as a vacuum evaporator, which may include a drum associated with a compressor as shown in the previous embodiment.

Pump 116a is configured to circulate LNG in pipe 118 from the bottom of tank 114 to auxiliary tank 130 to supply LNGs to and store in auxiliary tank 130.

In the devices in Fig. 8 and 9, the solution is to integrate the cooling means 170 into the ship's equipment in order to make the best use of this equipment to meet the needs of the ship. The cooling means 170 is such that when used

- for the type shown in Fig. 9, LNG is directed from tank 114 by pump 116a to cooling means 170 where it is cooled and then pumped to auxiliary tank 130 where it is stored; if the capacity of tank 130 is not sufficient for storage, the LNGs can be directed into pipe 132 and then through dip pipe 134 into tank 114, allowing the LNG in tank 114 to be cooled;

- for the second type shown in Fig. 8, the cooling means 170 directly cools the LNG stored in the auxiliary tank 130 while in direct contact with the LNG to produce LNGs.

In both cases, the result is that the LNGs are stored in the auxiliary tank 130. The temperature of the LNGs is preferably -180 to -160°C inclusive, which typically corresponds to a temperature drop of the LNG of -0.5 to -20°C. Due to the penetration of heat into the auxiliary tank 130, some of the LNGs may vaporize and turn into BOG 130b. If the pressure inside the auxiliary tank 130 reaches a predetermined threshold value, it can be controlled by removing part of the BOG using the compressor 126. The auxiliary tank 130 is made as intended and has, for example, a capacity of 50 to 500 m ³ to control the BOG at sea, or from 1500 to 10,000 m3 to control BOG at anchor ( ² to 5 days). The pressure in the auxiliary tank 130 is, for example, from 0.3 to 10 bar abs. inclusive, to provide flexibility in controlling pressure and boil-off gas 130b.

Cooling means 170 can be used independently of the solution and surrounding equipment. The cooling means 170 preferably operates continuously, whether or not cooling power is required.

If desired, LNGs may be directed to tank 114 via pipe 132 or dip pipe 134, for example, to control the pressure or temperature of the LNG contained in tank 114.

The pressure in tank 114 is typically controlled by pumping NBOG out of tank 114 by pumping NBOG through compressor 126 and through NBOG outlet 145 from tank 114. The NBOG coming from compressor 126 is then used to feed unit 112. If the load is on plant 112 is not sufficient to consume all of the NBOG, there is an excess of NBOG that needs to be disposed of. In this case, it is preferable to act only on the excess NBOG, and not on the LNG or all of the NBOG contained in the tank 114, as described above. Thanks to this solution, the excess NBOG coming from the compressor 126 at the operating pressure of the plant 112 (for example, 6-7 bar or 15-17 bar or 300-315 bar, depending on the type of installation on the ship), is sent to the heat exchanger 142, in which it is cooled by heat exchange with the NBOG withdrawn through the NBOG outlet 145 in the tank 114. The excess NBOG is then sent to the heat exchange circuit 140 of the tank 130, in which it will be cooled by heat exchange with the LNGs contained in this tank 130. The excess NBOG is then reduced pressure using the throttling valve 152 to the operating pressure of the drum 150 before it is fed into this drum 150. The drum 150 is regulated to a pressure similar to the storage pressure in the tank 114. Due to the location of the BOG condenser line (which includes the heat exchanger 142, circuit 140, the throttle valve 152 and drum 150), some of the excess NBOG condenses. Finally, the condensed NBOG recovered in drum 150 is re-pumped into tank car 114 via dip tube 134. (Re)condensing the NBOG in this way allows the NBOG pressure in tank car 114 to be reduced.

The device described above has many advantages, for example:

- Cooling means 170 is capable of handling all excess NBOG and continuously operating at medium power. Cooling means 170 is typically designed to either manage the maximum excess NBOG and then operate at lower powers to manage differences in excess NBOG, or operate at balanced power with loss of excess NBOG when this power is exceeded. Thanks to the device 110, the cooling means 170 can be selected depending on the average excess volume of NBOG and still be able to control the entire amount of excess NBOG. For a standard vessel, the average NBOG excess is in the range of 25 to 50% of the maximum NBOG excess. This flexibility in overcoming differences in cooling capacity production on the one hand and cooling capacity requirements on the other hand is gained by the auxiliary tank 130, which is able to store LNGs at a lower temperature than the LNG stored in tank 114. Thus , the refrigeration power is concentrated in LNGs and ready for use on demand, while in the prior art it is diluted inside the large tank volume 114.

- Cooling power is typically used to spray LNGs in tank 114. The vapor phase in tank 114 is cooled and partially condensed. From an energy point of view, this is not an ideal solution, as some of the excess NBOG can be used to feed plant 112. Through device 110, some of the NBOG is used to feed plant 112, and the cooling capacity is only used for the excess NBOG. For a typical vessel, gas consumption at anchor is between 15 and 30% of NBOG.

- Thanks to the compressor 126 installed on the ship, the excess NBOG is compressed to the inlet pressure of the 112 unit (typically 6-7 bar, 15-17 bar or 300-315 bar), and then cooled by LNGs and undergoes phase separation before returning to the main tank 114. This is more efficient than spraying the LNGs in the vapor phase in the main tank 114 because it allows more cooling of the excess NBOG and condensation of most of it due to the pressure difference.

- Some coolants may be used in specific conditions. For example, the vacuum evaporator described above can simply generate refrigeration from the additional FBOG needed in addition to the NBOG to be fed to plant 112. Through device 110, the cooling power generated can be used where and when needed.

In FIG. 9 and 10 show steps in the operation of the apparatus of FIG. 9, which naturally apply to the device of FIG. 8 and which may correspond to the stages of operation of a ship equipped with this device.

1. Regulation of conditions in the tank (pressure and temperature) - fig. nine;

2. Redundant NBOG control - fig. ten.

1. Regulation of conditions in the tank (pressure and temperature) - fig. nine.

If the auxiliary tank 130 does not need to be supplied with LNG from the tank 114 (for example, if the energy requirements are met by some other source of energy) and the conditions of the tank 114 need to be controlled (for example, a change in pressure or temperature before loading), then the LNGs contained in the auxiliary tank car 130 can be used to cool the LNG contained in tank car 114 by pumping it through pipe 132 and then dip pipe 134.

2. Redundant NBOG Management - FIG. ten.

As described above, excess NBOG can be disposed of by circulating it through the condenser line formed by heat exchanger 142, heat exchange circuit 140, throttle valve 152, and drum 150.

In FIG. 11 shows an alternative.

Because the plant requires a gas supply, typically at an inlet pressure greater than the storage pressure in tank 114, compressor 126 allows the NBOG to be pumped at a pressure acceptable in plant 112. During this compression, the NBOG heats up. The heat exchanger 142 is preferably used to recover some of the cold coming from the tank 114. This feature allows for performance improvements, but is not fundamental and therefore not necessary. As such, it has been removed from the embodiment of FIG. 11. The three-way valve outlet 146 is thus connected directly to the circuit inlet 140, and the NBOG tank outlet 145 is connected directly to the compressor inlet 126.

Fig. 12 is an embodiment of a device that differs from that shown in FIG. 9 in that it includes another heat exchanger 180. Heat exchanger 180 includes two circuits, namely a primary circuit 180a and a secondary circuit 180b.

Secondary circuit 180b has an inlet connected to a pump 182 submerged in LNGs contained in an auxiliary tank 130 and an outlet connected to an inlet of LNGs in tank 130 for reinjecting the LNGs into the tank after it has undergone heat exchange with the liquid medium. circulating in the primary circuit of the heat exchanger 180. The primary circuit 180 is similar to the circuit 140 of the heat exchanger described above.

Primary loop 180a is the hot loop. The liquid medium circulating in this circuit, in this case compressed BOG, is intended to be cooled by circulating in this circuit. Secondary circuit 180b is a cold circuit. The liquid medium circulating in this circuit, in this case LNGs from tank 330, is intended to be cooled by circulating in this circuit.

In FIG. 13 shows an embodiment of the device 10, which differs from the device in FIG. 1 in that drum 24 and auxiliary tank 30 are combined to form and define one tank 90 for forced stripping of LNG coming from tank 14 and storage of LNGs thus produced.

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

The second table shows the same types of parameters, but they are aimed at more general compositions of liquefied gas and, in particular, liquefied natural gas such as methane or mixtures of gases containing methane.

The hydrostatic pressure at the lower end of the pipe 18 (the pump is usually at a stable depth) varies depending on the fill level of the main tank.

The temperature of the liquefied gas in drum 24 is "temperature of BOG cooled by loop 40 °C" minus 2 °C, for example, corresponding to the "pinch effect" of the heat exchanger.

The proportion of gas evaporated after pressure reduction is calculated by the formula:

X = (Hl,u – Hl,d) / (Hv,d – Hl,d)

where:

X is the mass percentage of the evaporated liquid,

Hl,d (J/kg) is the enthalpy of the incoming fluid flow at incoming temperature and pressure,

Hv,d (J/kg) is the enthalpy of the evaporating gas at outlet pressure and corresponds to saturation temperature, and

Hl,d (J/kg) is the enthalpy of the residual liquid at outlet pressure and corresponds to the saturation temperature.

Claims (30)

1. Device (10, 110) for cooling natural stripping gas for installation (12, 112) for the production of energy, in particular, on board a ship, including - the main tank (14, 114) for storing liquefied gas, including the first outlet (45, 145) of natural stripping gas, - means (170 XXX) for receiving liquefied gas into the said main tank and cooling the liquefied gas, - an auxiliary tank (30, 130) for refrigerated liquefied gas, configured to store liquefied gas cooled by said cooling means, and - the first heat exchange circuit (40, 140), including an inlet pipe connected to the specified first outlet pipe of the specified main tank for the purpose of circulating natural stripping gas in the specified circuit, while the specified first circuit is configured to communicate with the specified auxiliary tank so that the specified gas natural stripping, passing through the specified first circuit, was cooled by cooled liquefied gas stored in the specified auxiliary tank or coming from the specified auxiliary tank. 2. The device (10, 110) according to the preceding paragraph, further comprising a first separation drum (50, 150), the inlet pipe of which is connected to the outlet pipe of said first circuit (40, 140) for supplying said first drum with cooled natural stripping gas and re- condensed natural stripping gas forming a refrigerated liquefied gas, wherein said first drum includes a first natural stripping gas outlet and a second refrigerated liquefied gas outlet connected to said main tank configured to pump the cooled liquefied gas into said main tank. 3. A device (10, 110) according to any one of the preceding claims, comprising at least one first compressor (26, 126), the inlet of which is connected to said first outlet of the stripping gas from said main tank (14, 114) and/ or with said first stripper gas outlet from said first drum (50, 150). 4. Device (10, 110) according to any one of the preceding claims, wherein said cooling means includes a second heat exchange circuit (172) which is configured to exchange heat with liquefied gas in said auxiliary tank (30, 130) or coming from said auxiliary tank tanks (30, 130), and in which the cooling liquid medium circulates, ensures the cooling of the said liquefied gas and the production of the refrigerated liquefied gas. 5. The device (10, 110) according to any one of paragraphs. 1-3, in which the specified cooling means includes - the second drum (24), the inlet of which is connected to the first end of the first pipe (18, 118), the second end of which is immersed in the liquefied gas contained in the specified main tank (14, 114), while the specified first pipe is made with the possibility of supplying into said first liquefied gas drum, and - the second pipe (31), the first end of which is connected to the first outlet pipe of the cooled liquefied gas of the said second drum and the second end of which is connected to the said auxiliary tank, configured to supply the said auxiliary tank (30, 130) with the cooled liquefied gas. 6. The device (10, 100) according to the preceding paragraph, including the first heat exchanger (60), the primary circuit (60a) of which has an inlet pipe connected to the outlet pipe of liquefied gas from the specified main tank (14), and an outlet pipe connected to the inlet branch pipe of the specified auxiliary tank (30), made with the possibility of supplying liquefied gas to the specified auxiliary tank, and the secondary circuit (60b) containing the inlet pipe connected to the specified first pipe (18), and the outlet pipe connected to the inlet pipe of the specified second drum ( 24). 7. Device (10, 110) according to claim 5 or 6, including - a first pump (16a, 116a) connected to said second end of said first pipe (18, 118) and immersed in said liquefied gas contained in said main tank (14, 114) so as to circulate the liquefied gas through said first pipe from said main tank to said second drum (24), and - a second pump (35) connected to said second pipe (31) so as to circulate cooled liquefied gas from said second drum (24) to said auxiliary tank (30, 130). 8. The device (10, 110) according to any one of paragraphs. 5-7, in which said first pipe (18, 118) includes an evaporation means (19). 9. The device (10, 110) according to any one of the preceding claims, including at least one second compressor (28, 128), the inlet pipe of which is connected to the specified first outlet pipe (45, 145) of the stripping gas from the specified main tank (14 , 114), while the specified second compressor includes an outlet pipe connected to the specified inlet pipe of the specified first circuit (40, 140). 10. The device (10, 110) according to any one of paragraphs. 5–8, wherein said inlet of said second compressor (28, 128) is further connected to a second gas outlet from said second drum (24) and/or to a second gas outlet from said first drum (50, 150). 11. The device (10, 110) according to paragraphs. 3, 9 or 10, wherein the inlet of said second compressor (28) is connected to the outlet of said first compressor (26). 12. The device (10, 110) according to any one of paragraphs. 9-11, in which said first or second compressor (26, 28, 126) includes an outlet pipe configured to supply fuel gas, in particular, to said installation (12, 112). 13. The device (10, 110) according to any one of paragraphs. 9-12, in which the specified inlet pipe of the specified first circuit (40, 140) is connected to the specified outlet pipe of the specified first or second compressor (26, 28, 126) through the primary circuit (42b, 142b) of the second heat exchanger (42, 142), while the second heat exchanger contains a secondary circuit (42a, 142a), the inlet pipe of which is connected to the specified first outlet pipe (45, 145) of natural stripping gas from the specified main tank (14, 114) and the outlet pipe of which is connected to the inlet pipe of the specified first or second compressor. 14. Device (10, 110) according to any one of the preceding claims, wherein said auxiliary tank (30, 130) is connected to the first end of a third refrigerated liquefied gas pipe (32, 132), the second end of which is connected to said main tank (14, 114), wherein said third pipe is configured to transport at least a portion of said refrigerated liquefied gas from said auxiliary tank to said main tank. 15. The device (10, 110) according to the preceding paragraph, in which the specified third pipe includes a dip pipe (34, 134), made with the possibility of immersion in the liquefied gas contained in the specified main tank (14, 114), and/or a spray manifold (22, 122) located in said main tank, configured to pump cooled liquefied gas into said main tank. 16. Vessel, in particular for the transport of liquefied gas, comprising at least one device (10, 110) according to any one of the preceding paragraphs. 17. The method of supplying fuel gas to the installation (12, 112) for the production of energy, in particular, on board the ship using the device (10, 110) according to any one of paragraphs. 1-15, including monitoring at least one parameter of gas consumption of the specified installation, and - the stage of preparation and storage of refrigerated liquefied gas, for example, in the specified auxiliary tank, if the value of the specified parameter is higher than the specified threshold value, - the stage of re-condensation of natural stripping gas produced in excess in the specified main tank, if the value of the specified parameter is below the specified threshold value. 18. The method according to the preceding claim, wherein the refrigerated liquefied gas is prepared if the natural stripping gas production is not sufficient to meet the gas demand of said plant. 19. The method according to the preceding claim, wherein the liquefied gas is cooled by receiving, expanding and separating phases of the liquefied gas contained in said main tank. 20. The method according to any one of paragraphs. 17-19, in which said refrigerated liquefied gas is stored in the main tank for condensing the stripping gas in this tank, in particular if the available amount of stripping gas in this tank exceeds the requirements of said installation.

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