DEVICE AND METHOD FOR SUB-COOLING A LIQUEFIED GAS

Abstract

TITLE OF THE INVENTION: DEVICE AND METHOD FOR SUBCOOLING A LIQUEFIED GAS The device (100) for subcooling a liquefied gas stream comprises: - a first subcooling heat exchanger (105), - a second subcooling heat exchanger (125), - an expansion valve (155) for an initial subcooled liquefied gas stream in liquid phase, the gas stream exiting the expansion valve being single-phase liquid, - a separator (145) configured to form two streams: - a first initial subcooled liquefied gas stream in liquid phase, and - a second initial subcooled liquefied gas stream in liquid phase, and - a recycling line (150) for the second initial subcooled liquefied gas stream in liquid phase, connected to the inlet for the recirculated expanded gas stream. liquid phase of the first heat exchanger, the second heat exchanger being configured so that, at the outlet,The gas flow has a temperature such that the flow at the outlet of the expansion valve is single-phase. Figure for the abbreviation: Figure 1,

Description

Title of the invention: DEVICE AND METHOD FOR SUBCOOLING A LIQUEFIED GAS Technical field of the invention

[0001] The present invention relates to a device for sub-cooling a liquefied gas and a method for sub-cooling a liquefied gas. It applies, in particular, to the field of the production of liquefied natural gas or liquefied biomethane. State of the art

[0002] The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been conceived or pursued previously. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section constitute prior art solely because of its inclusion in this section.

[0003] The principle of liquefying a gas (nitrogen, air, carbon dioxide or methane-rich gas for example) and storing it at pressures close to atmospheric pressure (typically less than 10 bara) is generally based on five fundamental steps, as shown in [Fig.3]: - a step 405 of compressing the gas to a value significantly higher than the storage pressure, here called “high pressure”, followed by cooling 410 to ambient temperature, - a pre-treatment step 415 serving in particular to avoid any crystallization of impurities in the gas liquefaction phase - a cooling step 420 with a view to liquefying and even sub-cooling the already liquid gas so that, during the final expansion (sometimes called “flash” or “end-flash”), the partial evaporation of the liquefied gas is sufficiently low (typically a vapor fraction of less than 40% mol) and - a final expansion or “end-flash” step 425, carried out for example through an expansion device (for example a Joule-Thomson valve), and configured to effectively go from the high pressure to the final storage pressure, which is significantly lower; at this step, part of the liquid therefore evaporates and is either recycled upstream of the initial compression or used by other processes.

[0004] Devices and methods implementing such a method generate steam during the final expansion of the liquefied gas. This formation of steam poses at least two technical problems: - first of all, transporting a two-phase fluid is always technically complex and unstable; which requires on the one hand a specific dimensioning of the pipeline connecting the final expansion system to the final storage and on the other hand strong geometric constraints (limit the length of this two-phase pipeline in order to limit the risks of stratified flows where vapor and liquid phases do not travel at the same speed) and - then, if impurities remain after the pretreatment phase, their crystallization depends notably on the phase of the solvent, here the liquefied gas: for a given temperature, the risk of crystallization of most of the impurities is considerably higher in the two-phase phase than in the pure liquid phase of the solvent; and the risk inherent in the crystallization of impurities is on the one hand the blockage and therefore the shutdown of the process and on the other hand the potential risk of damage to the equipment induced by the deposition of solids.

[0005] Some systems attempt to overcome these drawbacks by increasing the cooling of the liquefied gas, which involves an increase in the subcooling power and thus reduces the energy efficiency of such systems. Indeed, providing the necessary cold to sufficiently subcool the liquefied gas flow may in certain situations require increasing the required cooling power by at least 25%; because beyond the additional thermal load to be provided, the desired degrees of lowering being at temperatures lower or even significantly lower than that of the condensation range, the thermodynamic efficiency of the cycle is thermodynamically less good than at warmer temperatures.Thus, not only does this solution require more cold, but this cold is produced even less efficiently (than in the standard solution with limited subcooling), which ultimately generates an additional cost, both energy and economic, which is most of the time unacceptable in practice.

[0006] The specific sizing of the outlet pipes presents a risk of incorrect sizing of the pipes and therefore of instability of the process; the risk is also technical and economic because, as the final expansion of the liquefied gas in this approach does not support any formation of solid, it is necessary either to oversize the upstream pretreatment (which makes it possible to eliminate impurities which could crystallize at low temperature) or to take the risk of blocking the expansion system by deposit of crystallizing impurities. Summary of the invention

[0007] The present invention aims to remedy all or part of these drawbacks.

[0008] The general concept of the invention consists of: - for a specific gas to be liquefied, - for specific downstream conditions of use of the gas (storage or consumption, for example), in terms of pressure and temperature, - considering a determined number of stages or means of treatment of said gas at the outlet of a final heat exchanger, configuring the final heat exchanger so that at the outlet of at least one stage or at least one means of treatment, the liquid gas remains in a globally liquid state, that is to say in a single-phase state and that a part of this gas in a single-phase state is recycled, or recirculated, towards a heat exchanger contributing to the cooling of the gas to be liquefied or sub-cooled.

[0009] To this end, according to a first aspect, the present invention relates to a device for sub-cooling a flow of liquefied gas, which comprises: - a first intermediate sub-cooling heat exchanger, comprising: - an inlet for initial liquefied gas flow, acting as a hot source in the first heat exchanger, - an inlet for expanded gas flow recirculated in liquid phase, acting as a cold source in the first heat exchanger and - an outlet for the initial subcooled liquefied gas flow, in liquid phase, - a second final subcooling heat exchanger, comprising: - an inlet for the initial sub-cooled liquefied gas flow in the liquid phase, acting as a hot source in the second heat exchanger, - an inlet for subcooling fluid in the cold source in the first and second thermal and - an outlet for initial sub-cooled liquefied gas flow, in liquid phase, - an expander for the initial sub-cooled liquefied gas flow, in liquid phase, the liquefied gas flow leaving the expander being single-phase liquid, - a separator, downstream of the regulator configured to form two flows: - a first flow of initial sub-cooled liquefied gas, in liquid phase, and - a second flow of initial sub-cooled liquefied gas, in liquid phase, and - a recycling pipe for the second initial sub-cooled liquefied gas flow, in liquid phase, connected to the inlet for the recirculated expanded gas flow in liquid phase of the first heat exchanger, the second heat exchanger being configured so that, at the outlet, the initial sub-cooled liquefied gas, in liquid phase, has a temperature configured so that the initial sub-cooled liquefied gas flow, in liquid phase, at the outlet of the expander is single-phase liquid.

[0010] Thanks to these arrangements, the gas entering the separator is single-phase liquid, which allows: - long-term stability of the liquefaction process (no risk of crystallization or error in sizing two-phase pipes), - ease of sizing and design (no need to call on engineers specifically skilled in managing two-phase cryogenic flows), - additional process safety (no more risk of blockage and destruction by deposit of crystallizing impurity in cryogenic equipment) because it is directly controlled by the sub-cooling level (it is sufficient to control the final sub-cooling temperature knowing the composition of the liquefied gas to be certain of no generation of steam and therefore no risk of crystallization) and - all in an economical manner, that is to say with minimal modifications to existing equipment and minimal additional energy consumption.

[0011] The implementation of a regulator makes it possible to bring the gas into compliance with low pressure storage conditions compared to the pressure implemented in the device which is the subject of the present invention.

[0012] In particular embodiments, the separator is configured so that the second gas flow represents between 3% and 90% of the molar mass of the initial subcooled liquefied gas flow, in liquid phase, at the inlet of the separator.

[0013] In particular embodiments, the device which is the subject of the present invention comprises, upstream of the first exchanger: - a third cooling heat exchanger, comprising: - an inlet for initial gas flow, acting as a hot source in the third heat exchanger, - an inlet for cooling fluid flow in the cold source in the first heat exchanger and - an outlet for initial liquefied gas flow and - a supply line for the initial liquefied gas flow to the inlet for the initial liquefied gas flow of the first heat exchanger.

[0014] These embodiments make it possible to cool the gas flow, for example to at least the bubble temperature of the gas.

[0015] In particular embodiments, the device which is the subject of the present invention comprises, upstream of the first heat exchanger, a compressor of the initial gas flow. - These embodiments facilitate the subsequent condensation of the gas.

[0016] In particular embodiments, the device which is the subject of the present invention comprises, upstream of the first heat exchanger, a purifier of the initial gas flow. - These embodiments make it possible to remove most of the impurities from the initial gas flow.

[0017] In particular embodiments, the device which is the subject of the present invention comprises, upstream of the first heat exchanger, a heat exchanger configured to act on the initial gas flow. - These embodiments make it possible to cool the gas upstream of the liquefaction of this gas.

[0018] In particular embodiments, the device which is the subject of the present invention comprises, downstream of the first heat exchanger, a heat exchanger configured to act on the flow of recycled gas. - These embodiments make it possible to recover the remaining frigories contained in the liquid gas flow. -According to a second aspect, the present invention relates to a method for sub-cooling a flow of liquefied gas, which comprises: - a first stage of intermediate sub-cooling heat exchange, comprising: - an entry stage for initial liquefied gas flow, acting as a hot source, - an inlet stage for expanded gas flow recirculated in liquid phase, acting as a cold source and - an output stage for initial sub-cooled liquefied gas flow, in liquid phase, - a second stage of final subcooling heat exchange, comprising: - an inlet stage for initial sub-cooled liquefied gas flow, in liquid phase, acting as a hot source, - an inlet stage for subcooling fluid, acting as a cold source and - an output stage for initial sub-cooled liquefied gas flow, in liquid phase, - a stage of expansion of the initial sub-cooled liquefied gas flow, in liquid phase, the outlet liquefied gas flow being single-phase liquid, - a separation step, to form two flows: - a first flow of initial sub-cooled liquefied gas, in liquid phase, and - a second flow of initial sub-cooled liquefied gas, in liquid phase, and - a step of recycling the second initial sub-cooled liquefied gas flow, in liquid phase, to the inlet step for expanded gas flow recirculated in liquid phase of the first heat exchange step, the second heat exchange stage being configured so that, at the outlet, the initial sub-cooled liquefied gas flow, in liquid phase, has a temperature configured so that the initial sub-cooled liquefied gas flow, in liquid phase, at the outlet of the expansion stage is single-phase. Brief description of the figures

[0019] Other advantages, aims and particular characteristics of the invention will emerge from the following non-limiting description of at least one particular embodiment of the device and method which are the subject of the present invention, with reference to the appended drawings, in which:

[0020] [Fig.l] schematically represents a particular embodiment of the device which is the subject of the present invention,

[0021] [Fig.2] represents, schematically and in the form of a flowchart, a succession of particular steps of the method which is the subject of the present invention and

[0022] [Fig.3] schematically represents a particular embodiment of a device known from the prior art. Description of the embodiments

[0023] The present description is given without limitation, each characteristic of an embodiment being able to be combined with any other characteristic of any other embodiment in an advantageous manner.

[0024] It should be noted from now on that the figures are not to scale.

[0025] As understood from reading this description, various concepts The inventive methods may be implemented by one or more methods or devices described below, several examples of which are provided herein. The actions or steps performed in carrying out the method or device may be ordered in any suitable manner. Accordingly, it is possible to construct embodiments in which the actions or steps are performed in a different order than that illustrated, which may include performing certain acts simultaneously, even if they are shown as sequential acts in the illustrated embodiments.

[0026] The indefinite articles "a" and "an", as used in the description and claims, are to be understood as meaning "at least one", unless otherwise clearly indicated.

[0027] The expression "and / or", as used herein and in the claims, is to be understood to mean "either or both" of the elements so conjoined, i.e., elements which are present conjunctively in some cases and disjunctively in other cases. Multiple elements listed with "and / or" are to be interpreted in the same way, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present, other than the elements specifically identified by the "and / or" clause, whether or not related to those specifically identified elements. Thus, by way of non-limiting example, a reference to "A and / or B", when used in conjunction with open language such as "comprising" may refer, in a embodiment, to A only (possibly including elements other than B); in another embodiment, to B only (possibly including elements other than A); in yet another embodiment, to both A and B (possibly including other elements); etc.

[0028] As used herein in the description and in the claims, "or" is to be understood as having the same meaning as "and / or" as defined above. For example, when separating elements in a list, "or" or "and / or" is to be interpreted as being inclusive, i.e., the inclusion of at least one, but also more than one, number or list of elements, and, optionally, additional elements not listed. Only terms clearly indicating the contrary, such as "only one of" or "exactly one of", or, when used in the claims, "consisting of", refer to the inclusion of only one element of a number or list of elements. In general, the term "or" as used herein should only be construed as indicating exclusive alternatives (i.e., "either but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of."

[0029] As used in this specification and in the claims, the expression "at least one", with reference to a list of one or more elements, is to be understood to mean at least one element selected from one or more elements in the list of elements, but not necessarily including at least one of each element specifically listed in the list of elements and not excluding any combination of elements in the list of elements. This definition also allows for the optional presence of elements other than the specifically identified elements in the list of elements to which the expression "at least one" refers, whether or not related to those specifically identified elements.Thus, by way of non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B", or, equivalently, "at least one of A and / or B") may refer, in one embodiment, to at least one, optionally including more than one, A, without B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, without A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0030] In the claims, as well as in the description below, all transitional expressions such as "comprising", "including", "carrying", "having", "containing", "involving", "holding", "composed of", and the like, are to be understood as being open, that is to say as meaning including but not limited to. Only the transitory expressions "consisting of" and "consisting essentially of" are to be understood as closed or semi-closed transitory expressions, respectively.

[0031] As understood from reading this document, the present invention can be applied to a plurality of distinct gases, such as nitrogen, air, carbon dioxide or a methane-rich gas for example. Depending on the gas considered, the operating pressure and temperature values ​​of the method or device which is the subject of the present invention are adapted to achieve liquefaction of the gas at the phase conditions mentioned below.

[0032] A gas flow is said to be single-phase when the entire molar mass of its constituent is in a given phase (liquid, solid or vapor). Such a state is reached, for example, when the molar mass proportion of the liquid phase in the flow is equal to 100%.

[0033] It is noted that each inlet and / or outlet of an element of a hydraulic diagram is, for example, an opening in said element configured to be connected to a fluid transport pipe adapted to the nature of the fluid transported.

[0034] [Fig. 1], which is not to scale, shows a schematic view of an embodiment of the device 100 which is the subject of the present invention. This device 100 for sub-cooling a flow of liquefied gas comprises: - a first intermediate sub-cooling heat exchanger 105, comprising: - an inlet 110 for initial liquefied gas flow, acting as a hot source in the first heat exchanger, - an inlet 115 for expanded gas flow recirculated in liquid phase, acting as a cold source in the first heat exchanger and - an outlet 120 for initial subcooled liquefied gas flow, in liquid phase, - a second final subcooling heat exchanger 125, comprising: - an inlet 130 for initial subcooled liquefied gas flow, in liquid phase, acting as a hot source in the second heat exchanger, - an inlet 135 for subcooling fluid, acting as a cold source in the first and second thermal system and - an outlet 140 for initial liquefied gas flow, subcooled, in subcooled liquid phase, - a regulator 155 of the initial sub-cooled liquefied gas flow, in liquid phase, the liquefied gas flow at the outlet of the regulator being single-phase liquid, - a separator 145, downstream of the expander 155 configured to form two flows: - a first flow of initial sub-cooled liquefied gas, in liquid phase, and - a second flow of initial sub-cooled liquefied gas, in liquid phase, and - a pipe 150 for recycling the second initial sub-cooled liquefied gas flow, in liquid phase, connected to the inlet for expanded gas flow recirculated in liquid phase of the first heat exchanger, the second heat exchanger being configured so that, at the outlet, the initial sub-cooled liquefied gas flow, in liquid phase, has a temperature configured so that the initial sub-cooled liquefied gas flow, in liquid phase, at the outlet of the expander is single-phase liquid.

[0035] The first heat exchanger 105 has the function of sub-cooling the initial liquefied gas, at the inlet 110 of the first exchanger 105, by heat exchange with the flow of recirculated gas in the liquid phase, at the inlet 115 of the first exchanger 105.

[0036] At the inlet of the first exchanger 105, the initial gas is preferably in the at least partially liquid state and, preferably, generally in the liquid state. Thus, the initial liquefied gas at the inlet 110 of the first exchanger 105 is preferably at a temperature lower than the bubble temperature of said gas.

[0037] In other variants, the initial gas at the inlet 110 of the first exchanger 105 is in the vapor state.

[0038] Compared to the liquefaction of a conventional case, as shown in [Fig.3], where an external refrigeration cycle is used to cool the liquefied gas to a temperature equal to a value TD and where at the final expansion a quantity of vapor Xv>flash is generated, the present invention consists in pushing the subcooling to a temperature such that the separation or the final expansion does not generate any vapor.

[0039] As understood, the main subcooling range is thus achieved using a fraction of the final liquefied gas used as a cold supply. This fraction of liquefied gas is at the pressure of a storage 101 and is therefore the fraction which is diverted from the filling flow of the storage 101; the value of this fraction is typically equal (to within a few percent) to XVjflash, that is to say the equivalent fraction of steam which is generated in the standard case when the same expansion is achieved but starting from a subcooled liquefied gas only at the temperature TD.

[0040] The second heat exchanger 125 has the function of sub-cooling the initial liquefied gas at the outlet of the first heat exchanger 105 in contact with a cooling fluid at a determined temperature such that the liquid gas at the outlet of the separator 145 is single-phase and in liquid phase.

[0041] At the inlet of the second exchanger 125, the initial liquefied gas is preferably in the at least partially liquid state and, preferably, generally in the liquid state. Thus, the initial liquefied gas at the inlet 130 of the second exchanger 125 is preferably at a temperature lower than the bubble temperature of said gas.

[0042] The separator 145 may be of any type suitable for separating a fraction of a liquid in a flow passing through this separator 145. The proportion of second flow to separate from the first stream may be a constant value or a value determinable based on, for example, the flow rate of gas passing through the device 100.

[0043] The recycling pipe 150 is, for example, of any type suitable for transporting the gas used by the device 100 in liquid phase.

[0044] This final subcooling range, ensuring the lowering of the temperature of the liquefied gas to a temperature allowing no vapor to be generated during separation and / or expansion, is restricted to a cooling of a few degrees (typically this range extends over less than 10°C and preferably less than 5°C). This subcooling is carried out, for example, using an external refrigeration cycle. Such an external cycle, in the case of the liquefaction of a methane-rich gas, can be for example an open cycle with liquid nitrogen or a reverse Brayton cycle. As the subcooling range is very restricted, the excess energy consumption by a conventional process is very limited (of the order of a few percent more than the energy consumption of the cooling cycle in the standard case shown in [Fig.3]). - The regulator 155 is, for example, a Joule-Thomson valve or any other commonly known expansion member for the expansion of a liquefied gas. Such a storage 101 is, for example, a tank suitable for the retention and transport of liquefied natural gas. When such a regulator 155 is implemented, the device 100 is configured so that, at the outlet of the regulator 155, the liquefied natural gas remains single-phase and in the liquid phase. - In particular embodiments, the separator 145 is configured so that the second gas flow represents between 3% and 90% of the molar mass of the initial sub-cooled liquefied gas flow, in liquid phase, at the inlet of the separator. - In particular embodiments, the device 100 which is the subject of the present invention comprises, upstream of the first heat exchanger 105: - a third cooling heat exchanger 160, comprising: - an inlet 165 for initial gas flow, acting as a hot source in the third heat exchanger, - an inlet 170 for a flow of cooling fluid, acting as a cold source in the first heat exchanger; this flow 170 may for example be part of a reverse Brayton type cooling cycle and - an outlet 175 for an initial flow of liquefied gas and - a pipe 180 for supplying the initial liquefied gas flow to the inlet 110 for the initial liquefied gas flow of the first heat exchanger 105.

[0045] The third heat exchanger 160 has the function of reducing the quantity of liquefied gas diverted to carry out subcooling in the first heat exchanger 105.

[0046] In particular embodiments, the device 100 which is the subject of the present invention comprises, upstream of the first heat exchanger 105, a compressor 185 of the initial gas flow.

[0047] Such a compressor 185 may be of any type suitable for the initial gas to be liquefied. Such a compressor 185 is, for example, a centrifugal compressor.

[0048] In variants, the recycling line 150 is configured to be connected to the compressor 185 so that, after exchange in the first heat exchanger 105, the fraction separated in the separator 145 is supplied to the compressor 185. This fraction is then partially liquid, partially vaporized or completely vaporized.

[0049] In particular embodiments, the device 100 which is the subject of the present invention comprises, upstream of the first heat exchanger 105, a purifier 190 of the initial gas flow. - The nature and operating parameters of the purifier 190 depend on the type of impurities to be removed from the initial gas flow. Such a purifier 190 may be an activated carbon filter or an evaporator, for example.

[0050] In particular embodiments, the device 100 which is the subject of the present invention comprises, upstream of the first heat exchanger 105, a heat exchanger 195 configured to act on the initial gas flow. - The heat exchanger 195 is, for example, configured to pre-cool the initial gas upstream of implementation by the third heat exchanger 160 or the first heat exchanger 105.

[0051] In particular embodiments, the device 100 which is the subject of the present invention comprises, downstream of the first heat exchanger 105, a heat exchanger 200 configured to act on the flow of recycled gas. - The heat exchanger 200 is, for example, configured to collect frigories from the recycled gas. - In [Fig.2], we observe schematically an embodiment of the method 300 which is the subject of the present invention. This method 300 for sub-cooling a flow of liquefied gas comprises: - a first stage 305 of intermediate sub-cooling heat exchange, comprising: - an inlet step 310 for the initial liquefied gas flow, acting as a hot source, - an inlet step 315 for the expanded gas flow recirculated in the liquid phase, acting as a cold source and - an outlet step 320 for the initial sub-cooled liquefied gas flow, in liquid phase, - a second stage 325 of final subcooling heat exchange, comprising: - an inlet step 330 for initial sub-cooled liquefied gas flow, in liquid phase, acting as a hot source, - an inlet stage 335 for subcooling fluid, acting as a cold source and - an outlet step 340 for the initial sub-cooled liquefied gas flow, in liquid phase, - a step 355 of expansion of the initial sub-cooled liquefied gas flow, in liquid phase, the outlet gas flow being single-phase liquid, - a separation step 345, to form two flows: - a first initial sub-cooled liquefied gas flow, in liquid phase, and - a second initial sub-cooled liquefied gas flow, in liquid phase, and - a step 350 of recycling the second initial sub-cooled liquefied gas flow, in liquid phase, to the inlet step for expanded gas flow recirculated in liquid phase of the first heat exchange step, the second heat exchange stage being configured so that, at the outlet, the initial sub-cooled liquefied gas flow, in liquid phase, has a temperature configured so that the initial sub-cooled liquefied gas flow, in liquid phase, at the outlet of the expansion stage is single-phase.

[0052] We also observe, in [Fig.2], an upstream step 301 of treatment and liquefaction of a natural gas to be liquefied, this step 301 corresponding, for example, to at least one treatment carried out on the gas upstream of the thermal reactor 105 in [Fig.l].

[0053] Embodiments of the method 300 which is the subject of the present invention are described with regard to the device 100 as described with regard to [Fig.l].

[0054] The following summary table illustrates a non-limiting operational example, comparing the current approach, represented in [Fig. 3], and the approach of the present invention, represented in Figures 1 and 2. At the inlet, the gas to be liquefied is here considered to comprise LNG vapor, called BOG (for “Boil off gas”, or evaporation gas), at low pressure and composed of 100% methane.

[0055] [Tableauxl] Circuit point ABDFG A' E' E” G' F' Approach shown in Figure 3 Mass flow rate (kg / h) 100 143, 1 143, 1 43.1 100 43.1 Temperature (°C) 30 30 -108 -111 -153 30 -114 ,1 -152 ,6 Pressure (bara ) 1 20 20 2 2 1 20 2 Approach shown in figures 1 and 2 Mass flow rate (kg / h) 100 143, 1 142 42 100 42 Temperature (°C) 30 30 -108 -111 -153 30 -152 ,3 - 153 ,2 -152 ,6 -152 ,6 Pressure (bara ) 1 20 20 2 2 1 20 20 2 2

[0056] In this example: - the bubble temperature at point D is -108°C and - the mass ratio of the part directed towards point F to the mass directed towards the reservoir is 30%.

[0057] In this example, the temperature difference to be bridged by the approach shown in Figures 2 and 3 at the level of the heat exchangers is less, in particular in the second exchanger between E' and E” where the excess cooling to be provided is only 0.9°C.

Claims

1. Claims Device (100) for sub-cooling a flow of liquefied gas, characterized in that it comprises: - a first intermediate sub-cooling heat exchanger (105), comprising: - an inlet (110) for initial liquefied gas flow, acting as a hot source in the first heat exchanger, - an inlet (115) for a flow of expanded gas recirculated in liquid phase, acting as a cold source in the first heat exchanger and - an outlet (120) for initial sub-cooled liquefied gas flow, in liquid phase, - a second final subcooling heat exchanger (125), comprising: - an inlet (130) for a flow of initial sub-cooled liquefied gas, in liquid phase, acting as a hot source in the second heat exchanger, - an inlet (135) for subcooling fluid in the cold source in the second heat exchanger and - an outlet (140) for initial liquefied gas flow, subcooled, in subcooled liquid phase, - an expander (155) for the initial sub-cooled liquefied gas flow, in liquid phase, the liquefied gas flow leaving the expander being single-phase liquid, - a separator (145), downstream of the regulator (155) configured to form two flows: - a first flow of initial sub-cooled liquefied gas, in liquid phase, and - a second flow of initial sub-cooled liquefied gas, in liquid phase, and - a pipe (150) for recycling the second initial sub-cooled liquefied gas flow, in liquid phase, connected to the inlet for expanded gas flow recirculated in liquid phase of the first heat exchanger, the second heat exchanger being configured so that, at the outlet, the initial subcooled liquefied gas flow, in the liquid phase, has a temperature less than or equal to the temperature at the outlet of the expander so that the initial subcooled liquefied gas flow, in liquid phase, at the outlet of the expander is single-phase liquid.

2. Device (100) according to claim 1, in which the separator (145) is configured so that the second gas flow represents between 3% and 90% of the molar mass of the initial sub-cooled liquefied gas flow, in liquid phase, at the inlet of the separator.

3. Device (100) according to one of claims 1 or 2, which comprises upstream of the first heat exchanger (105): - a third cooling heat exchanger (160), comprising: - an inlet (165) for initial gas flow, acting as a hot source in the third heat exchanger, - an inlet (170) for cooling fluid flow, acting as a cold source in the first heat exchanger and - an outlet (175) for initial liquefied gas flow and - a pipe (180) for supplying the initial liquefied gas flow to the inlet for initial liquefied gas flow of the first heat exchanger.

4. Device (100) according to one of claims 1 to 3, which comprises, upstream of the first heat exchanger (105), a compressor (185) of the initial liquefied gas flow.

5. Device (100) according to one of claims 1 to 4, which comprises, upstream of the first heat exchanger (105), a purifier (190) of the initial liquefied gas flow.

6. Device (100) according to one of claims 1 to 5, which comprises, upstream of the first heat exchanger (105), a heat exchanger (195) configured to act on the initial flow of liquefied gas.

7. Device (100) according to one of claims 1 to 6, which comprises, downstream of the first heat exchanger (105), a heat exchanger (200) configured to act on the recirculated gas flow.

8. Method (300) for subcooling a liquefied gas flow, characterized in that it comprises: - a first step (305) of intermediate subcooling heat exchange, comprising: - an inlet step (310) for initial liquefied gas flow, acting as a hot source, - an inlet step (315) for expanded gas flow recirculated in liquid phase, as a cold source and - an outlet step (320) for the initial sub-cooled liquefied gas flow, in liquid phase, - a second stage (325) of final sub-cooling heat exchange, comprising: - an inlet step (330) for an initial sub-cooled liquefied gas flow, in liquid phase, acting as a hot source, - an inlet stage (335) for subcooling fluid acting as a cold source and - an outlet step (340) for the initial sub-cooled liquefied gas flow, in liquid phase, - a step of expansion (355) of the initial sub-cooled liquefied gas flow, in liquid phase, the outlet liquefied gas flow being single-phase liquid, - a separation step (345), to form two flows: - a first flow of initial sub-cooled liquefied gas, in liquid phase, and - a second flow of initial sub-cooled liquefied gas, in liquid phase, and - a step (350) of recycling the second initial sub-cooled liquefied gas flow, in liquid phase, to the inlet step for expanded gas flow recirculated in liquid phase of the first heat exchange step, the second heat exchange stage being configured so that, at the outlet, the initial sub-cooled liquefied gas flow, in liquid phase, has a temperature less than or equal to the temperature at the outlet of the expansion stage so that the initial sub-cooled liquefied gas flow, in liquid phase, at the outlet of the expansion stage is single-phase.

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