BR112019013025A2 - device and method for liquefying natural gas and vessel comprising the device - Google Patents

Abstract

device (600) for liquefying a natural gas comprising: - a first centrifugal compressor (605), - a fractionation medium (110), - a second centrifugal compressor (610), - a first heat exchanger body (115), - a second heat exchanger body (120), and - a return duct (125) leading to the first compressor, - upstream of an inlet (116) in the first heat exchanger body, a third heat exchanger body (420) - a third centrifugal compressor (620), the first and third centrifugal compressors being driven by a single turbine in common (630), - a housing (635) common to the first compressor and the third compressor, - a cooling medium (430) , and - a transfer duct (435) leading to the third exchange body.

Description

DEVICE AND METHOD FOR NATURAL GAS LIQUEFACING AND VESSEL UNDERSTANDING THE DEVICE

TECHNICAL FIELD OF THE INVENTION [0001] The present invention relates to a device for liquefying a natural gas, a process for liquefying a natural gas and a container comprising such a device. It applies in particular to the liquefaction of offshore or onshore natural gas.

STATE OF THE TECHNIQUE [0002] The liquefaction of natural gas allows it to be transported in a smaller volume compared to the transport of non-liquefied natural gas.

[0003] In recent decades, liquefaction technologies have targeted large gas capacities for reasons of economies of scale.

[0004] The implementation of the technologies used in this way requires very high investments and presents very high transport costs (liquefaction and maritime reception infrastructures). So first, on the one hand, the tendency of the liquefaction capacity has been to increase the volume of natural gas transported to obtain economies of scale and make these projects more economically attractive. Second, the investments made to implement these technologies are aimed at this dimensioning and the construction of liquefaction processes needed to be as effective as possible to minimize operating costs from then on.

[0005] Currently, the number of large-scale projects has decreased dramatically and there is renewed interest in the production of small capacity of liquefied natural gas at

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2/39 from natural gas or biogas.

[0006] Indeed, the valorisation of small sources of gas, by-product gases and biogas are new opportunities promoted notably by the environmental awareness of populations and governments or by the desire to reach an isolated consumer in areas without gas and / or transport infrastructure. distribution. These opportunities, however, are too small to justify the use of technologies for large-scale production (the transposition of traditional technologies is not relevant because it is very complex and does not justify the economic viability of these new projects), hence the need to propose new technologies that can address the two main issues related to small-scale liquefaction:

- reduction of investment costs as much as possible, keeping efficiency as high as possible, in order to minimize operating costs; and

- increased process efficiency to minimize product loss: the volumes of gas to be recovered are low, making each molecule important. Currently, offshore and nearshore gas resources are in full swing, leading to the use of technological solutions adapted to marine environments that are known as FLNG (for Floating Liquefied Natural Gas).

[0007] In particular, several types of liquefaction cycles are known:

- cascade cycles,

- mixed refrigerant cycles and

- expansion cycles.

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3/39 [0008] Liquefaction cycles are based on these cycles or a combination of these cycles. This is particularly the case with the Integral Cascading Incorporated aka CII process.

[0009] In the CII system:

- a refrigerant mixture is compressed and then fractionated into a heavy fraction and a light fraction,

- the heavy fraction being used in a first plate heat exchanger to exchange heat between this heavy fraction and the natural gas to cool it,

- the light fraction is compressed,

- the light fraction is used in a second plate heat exchanger between this light fraction and the cooled natural gas, in order to liquefy that natural gas; and the two fractions of the heated mixture are then collected and compressed again.

[0010] This system has several disadvantages:

- plate heat exchangers are very sensitive to fluid distribution, which represents a problem of marine adaptation for marine applications,

- the refrigerant mixture has a large number of components, especially heavy compounds, these compounds crystallize in heat exchangers under particular conditions of pressure and temperature whose advent is not easily predictable and

- the method has limited flexibility, especially in terms of operational flow and limited production capacity by means of compression.

[0011] In process CII, the cooling mixture is a mixture of nitrogen and hydrocarbons (methane, ethane,

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4/39 ibutane, n-butane, i-pentane and n-pentane). The partial vaporization of this low pressure mixture makes it possible to cool, liquefy natural gas and cool the LNG produced:

- the low pressure vaporization of the heavy fraction of the refrigerant mixture (gas at the top of the fractionation column) makes it possible to contribute to the negative heating required to cool the natural gas; and

- the light fraction will make it possible to liquefy natural gas and super-cool the LNG.

[0012] At the outlet of the exchanger pipe, the refrigerant mixture is completely vaporized.

[0013] The CII system has the main disadvantages:

- the CII method was developed for the production of large-scale LNG onshore;

- the method is not very flexible: efficiency drops significantly with any deviation from the point of operation / design,

- the refrigerant mixture contains many constituents (hydrocarbons), which makes the logistics and the operational aspect more complex;

- storage increases the weight of the installations, which is critical in offshore installations;

- the method presents difficulties in the supply of ethane, which represents major problems in offshore installations;

- the method presents risks of deterioration of the equipment (exchangers) due to the risk of crystallization of the pentane (iC5 and nC5) contained in the cooling mixture;

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- the efficiency of the method is limited by the dimensions of the exchanger and the constraints related to manufacturing; and

- the method presents problems with offshore equipment installation (significant drop in the performance of the heat exchanger if the distribution is not correct).

[0014] The CII process is based on a simple compression line using centrifugal compressors.

[0015] A centrifugal compressor serves to compress a gas and, consequently, to increase its pressure. Centrifugal compressors are equipped with wheels rotating around an axis driven by a turbine or an electric motor. These rotating wheels make it possible to transform the kinetic energy contained in the gas into potential energy, in order to increase its pressure.

[0016] As the possible pressure increase that can be achieved by a wheel is limited, it is necessary to multiply the number to achieve the desired discharge pressure.

[0017] The set of wheels is contained in a body called casing. A casing can contain a maximum number of wheels between eight and ten, and the higher the number, the more likely the compressor is to have stability problems.

[0018] Compression is the heart of a liquefaction process. In fact, each additional point of efficiency, in addition to the compressor, increases the production of liquefied natural gas.

[0019] In addition, the compression train is the most expensive component of a liquefaction unit.

[0020] Increasing the efficiency of a centrifugal compressor results in an increase in investment. For another

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6/39 on the other hand, reduced investment leads to less effective and / or dramatically less flexible solutions.

[0021] The financial value of a compressor is directly related to the number of wrappers. In fact, the greater the number of envelopes, the greater the investment to be made, but the greater the operational flexibility. On the other hand, the decrease in the number of wrappers leads to a loss of operational flexibility, sometimes accompanied by a loss of efficiency.

[0022] The challenge of the present invention is, therefore, to provide a better compromise between efficiency and investment, in order to maintain a satisfactory performance in a range of operation as wide as possible.

[0023] The compression trains of the CII process comprise a low and medium pressure section and a high pressure compression section. The compression stages are grouped into one, two or three shells.

[0024] The low and medium pressure section makes it possible to compress the low pressure refrigerant mixture at the outlet of the cryogenic exchange tubing.

[0025] The high pressure section makes it possible to compress the light fraction of the refrigerant mixture that will provide the negative heat necessary for the liquefaction and subcooling of the liquefied natural gas.

[0026] The actuation, by the same axis, of low and high pressure sections in the compression train, causes a single rotation between the turbines of these sections. This rotation speed can be differentiated by the use of multiplication mechanisms between the rotation speed of the turbines in relation to the single axis. However, with or without a mechanism

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7/39 of multiplication, the rotation speeds must necessarily be proportional or identical, depending on the case, which makes the compression train non-flexible when the flow rates entering each section are not identical or proportional. This can cause mechanical stability problems.

[0027] In addition, a significant drop in efficiency in the high pressure section, even more marked when it is desired to include both sections in the same enclosure.

[0028] Finally, this configuration is not very flexible, which limits the scope of opportunities that can be addressed: there is a drop in efficiency that can be significant if there is a deviation from the operating point for which the equipment was designed (gas and precise production conditions) and mechanical stability problems may occur, leading to more frequent maintenance.

[0029] The current IIC systems have the following disadvantages:

- a variation in the flow between the low pressure and the high pressure section of the compression train which leads to an imbalance between these two sections, which can lead to problems of mechanical instability during the stop and start stages,

- a significant drop in efficiency is observed between the low pressure and high pressure section; and

- limited flexibility of the compression train in terms of flow rate and composition.

[0030] For example, the teachings of US 6,347,532, US 2015/152884, US 2011/259045, US are known

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6,023,942 and US 4,755,200. However, none of these documents makes it possible to compact the device and their combination would cause problems with the mechanical stability of the shaft that compresses the refrigerant mixture.

OBJECTIVE OF THE INVENTION [0031] The present invention aims to remedy all or part of these disadvantages.

[0032] For this purpose, according to a first aspect, the present invention relates to a device for liquefying a natural gas, comprising:

- a first centrifugal compressor from a first vaporized refrigerant chemical mixture,

- device for fractionating the compressed mixture into a heavy fraction and a light fraction,

- a second centrifugal compressor of the light fraction,

- a first heat exchanger body between the heavy fraction of the first mixture and the natural gas to cool at least the natural gas,

- a second heat exchanger body between the compressed light fraction of the first mixture and the cooled natural gas in the first heat exchanger body for liquefying the natural gas, and

- a return line from the first refrigerant mixture vaporized in the heat exchange bodies to the first compressor, comprising:

- a third heat exchanger body for heat exchange between natural gas and a second refrigerant chemical compound are upstream of a natural gas inlet in the first heat exchanger body,

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- a third centrifugal compressor of the second vaporized compound, in which the first and third centrifugal compressors are driven by a single turbine in common,

- a housing common to the first compressor and the third compressor,

- device for cooling the second compressed compound,

- a conduit for transferring the second cooled compound to the third exchange body,

- between the second compressor and the second exchanger body, there are the second and fourth centrifugal compressors driven by a single turbine in common, and

- a housing common to the second compressor and the fourth compressor.

[0033] These provisions allow:

- significantly reduce the cost of manufacturing the device;

- the device has a wide operational range in terms of composition and flow;

- the device has a better balance between the compression sections; and

- the process performed by the device to be more robust, allows stops and more frequent start.

[0034] In addition, the use of two different exchange bodies makes it possible to better control the heat exchanges that occur in each said exchange body. Finally, the use of four compressors allows a better compression balance along the heat exchange pipe to maximize the efficiency of each compression section.

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10/39 [0035] In some embodiments, the turbine that operates the first and third compressors and the turbine that operates the second and fourth compressors are mechanically coupled.

[0036] In some modalities, the turbines are combined.

[0037] These modalities make it possible to reduce the size of the device.

[0038] In some embodiments, the device that is the subject of the present invention comprises:

- a separator of a gas fraction and a liquid fraction of the compressed light stage, the fourth compressor compressing the separated gas fraction;

- a regulator of the liquid fraction of the heated light stage in the second exchanger body,

- the turbine of the fourth compressor being driven by expansion energy.

[0039] In some embodiments, the second chemical compound comprises a pure substance consisting of nitrogen, propane and / or ammonia.

[0040] The use of such a composition to form the second compound makes it possible to cool the natural gas before this natural gas enters the exchange pipe formed by the first and second exchange bodies. This pre-cooling allows to simplify / limit the number of constituents in the first refrigerant mixture used, which also allows to reduce the dimensions of the exchange surfaces between natural gas and the first refrigerant mixture.

[0041] In some embodiments, the first refrigerant mixture comprises nitrogen and methane and at least one

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11/39 among:

- ethylene,

- ethane,

- propane and / or

- butane.

[0042] The use of such a mixture minimizes the energy supply in the system for liquefying natural gas.

[0043] In fact, in the CII system as currently implemented, heavy compounds are used in the first refrigerant mixture, these compounds having the advantage of guaranteeing the vaporization of the first mixture before entering the first compressor.

[0044] However, these heavy compounds have the disadvantage of crystallizing in the coldest portion of the exchanger, depending on the content of these compounds and a possible temporary overcoming of operating conditions. So far, there is no clear and universal limit for determining when crystallization occurs, leading to uncertainty and risk of damage. However, the person skilled in the art, who currently favors the gaseous state of the first mixture at the entrance of the first compressor, uses this type of compounds despite this disadvantage.

[0045] In some embodiments, the device that is the object of the present invention comprises:

- a liquefied natural gas regulator,

- an evaporator gas collector produced during the expansion of the gas in the regulator, and

- a conduit for injection of evaporation gas at the entrance of the second exchanger body.

[0046] In some modalities, the cooling medium

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12/39 of the second compound comprises an outlet for the second compound, the device comprising, between said outlet and the third exchange body, a cooling circuit of the second compound with a heavy fraction of the first mixture within the first exchange body.

[0047] These modalities make it possible to cool the second compound in the cascade of exchangers formed by the first and second exchangers.

[0048] In some embodiments, the first exchange body and / or the second exchange body are a spiral exchanger.

[0049] In some embodiments, the cooling medium of the second compound is a heat exchanger between the second compound and the water.

[0050] According to a second aspect, the present invention relates to a method for liquefying a natural gas, comprising:

- a first stage of centrifugal compression of a first vaporized refrigerant chemical mixture,

- a fractionation step of the compressed mixture into a heavy fraction and a light fraction,

- a second stage of centrifugal compression of the light fraction,

- a first heat exchange step between the heavy fraction of the first mixture and natural gas to cool at least natural gas,

- a second heat exchange step between the light compressed fraction of the first mixture and the cooled natural gas in the first exchanger body for liquefying the natural gas, and

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- a return step of the first vaporized refrigerant mixture during the heat exchange steps for the first compression step, which comprises:

- upstream of a natural gas entry stage in the first exchange stage, a third heat exchange stage between natural gas and a second refrigerant chemical compound,

- a third stage of centrifugal compression of the second vaporized compound, the first and third stages of centrifugal compression being driven by a single turbine in common,

- the first and third stages of compression being performed in a common enclosure,

- a cooling step of the second compressed compound during the third exchange step,

- a transfer step from the second cooled compound to the third exchange step,

- between the second stage of compression and the second stage of exchange, a fourth stage of compression of the light fraction of the first mixture, the second and fourth stages of compression being driven by a single turbine in common, and

- the first and third stages of compression being carried out in a common enclosure.

[0051] Since the objectives, advantages and particular characteristics of the method, which are the subject of the present invention, are similar to those of the device which is the object of the present invention, they will not be repeated in this document.

BRIEF DESCRIPTION OF THE FIGURES

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14/39 [0052] Other advantages, objectives and particular features of the invention will emerge from the following non-limiting description, of at least one realization of the device, vessel and method that are the subject of the present invention, with respect to attached drawings, in which:

figure 1 schematically represents a first particular embodiment of the device which is the object of the present invention,

- figure 2 represents, schematically, a particular modality of the vessel that is the object of the present invention,

figure 3 represents, schematically and in the form of a logic diagram, a first particular sequence of steps in the method which is the object of the present invention;

figure 4 schematically represents a second particular embodiment of the device which is the subject of the present invention;

figure 5 represents, schematically and in the form of a logical diagram, a second particular sequence of steps of the method which is the subject of the present invention;

figure 6 schematically represents a third particular embodiment of the device which is the subject of the present invention;

- figure 7 represents, schematically, a particular modality of the compressors of the device which is the object of the present invention

figure 8 schematically and in the form of a logical diagram, a third particular sequence of steps in the method which is the subject of the present invention.

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DESCRIPTION OF EXAMPLES OF CARRYING OUT THE INVENTION [0053] The present description is provided in a non-limiting mode, each feature of a modality being able to be combined with any other feature of any other modality in an advantageous manner.

[0054] It is observed that the numbers are not to scale.

[0055] Figure 1, which is not to scale, shows a schematic view of an embodiment of device 100, which is the object of the present invention. This device 100 is intended for the liquefaction of a natural gas, comprising:

- a compressor 105 of a first vaporized refrigerant chemical mixture,

- means 110 for fractionating the compressed mixture into a heavy fraction and a light fraction,

- a first heat exchanger body 115 between the heavy fraction of the first mixture and the natural gas intended to cool at least the natural gas;

- a second heat exchanger body 120 between the light fraction of the first mixture and the cooled natural gas in the first heat exchanger body for liquefying the natural gas, and

- a conduit 125 for returning the first vaporized refrigerant mixture to the heat exchange bodies for compressor 105, which comprises:

- upstream of a natural gas inlet 116 in the first exchange body 115 or downstream of a liquefied natural gas outlet 121 of the second exchange body 120, a third body, 130 or 135 for heat exchange between natural gas and a second chemical soda and

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- a means, 140 or 145, for compressing the second vaporized compound.

[0056] Compressor 105 is, for example, a centrifugal compressor equipped with a wheel rotating around an axis driven by a turbine or an electric motor. This rotating wheel makes it possible to transform the kinetic energy contained in the gas into potential energy, in order to increase the pressure of that gas. In order to increase the compression achieved, the number of wheels is increased to achieve a certain discharge pressure.

[0057] The inlet pressure of compressor 105 is, for example, on the order of at least 2 bar (0.2 MPa) absolute. The compression ratio achieved in the compressor 105 is, for example, between 2 and 6.

[0058] This compressor 105 is, for example, configured to compress a first refrigerant mixture that comprises nitrogen and methane and at least one among:

- ethylene,

- ethane,

- propane, and / or

- butane.

[0059] The composition of the first compound is adjusted according to the composition of the natural gas to be liquefied in the device. This adjustment is made according to the steam function curve, that is, the equilibrium pressure temperature, of the composition of the natural gas along the exchange pipe formed by the first body 112 and the second exchange body 120.

[0060] The use of propane aims to balance the differences in volatility between heavy compounds and compounds

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17/39 light of the first mixture.

[0061] This compressor 105 includes an inlet (not numbered) for the vaporized refrigerant mixture and an outlet (not numbered) for the compressed refrigerant mixture.

[0062] The compressed refrigerant mixture is preferably cooled in a fifth heat exchanger 106. This heat exchanger 106 is, for example, a tubular exchanger, in which the cold source is air or water. The colder the source temperature, the greater the efficiency of the process. Preferably, the maximum cooling temperature corresponds to the air or water temperature plus fifteen degrees Celsius.

[0063] The cooling mixture, preferably cooled in the fifth exchanger 106, is supplied by means (110) for fractionation. The means (110) for fractionation means, for example, a fractionation column.

[0064] The flow that enters the fractionation column is diphasic, that is, of two stages, being a gaseous portion and a liquid portion. The gas fraction flows in the column to exit at the top and the liquid fraction at the bottom.

[0065] This means (110) for fractionation comprises:

- an (unnumbered) inlet for a compressed refrigerant mixture,

- an outlet (unnumbered) for a light fraction of the refrigerant mixture positioned at the bottom of the fractionation means 110 and

- an outlet (unnumbered) for a heavy fraction of the refrigerant mixture at the top, in relation to the outlet

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18/39 of the light fraction, of the medium (110) for fractionation.

[0066] Preferably, the light fraction that leaves the medium (110) for fractionation enters the first exchange body 115 and is cooled by the heavy fraction that passes through the first exchange body 115. This light fraction can also, depending on the operating conditions , act as a cold source in the heat exchange that occurs with the natural gas that enters through the inlet 116 of the first exchanger body 115.

[0067] In some preferred embodiments, the means (110) for fractionation further comprises an inlet for refluxing a portion of the light fraction, this portion of the light fraction being collected, for example, from a reflux drum 111.

[0068] The fractionation medium (110) then preferably comprises packaging which makes it possible to improve the transfer of material between the gas flow and the liquid fraction of the reflux drum 111, which absorbs the heavier compounds of the gas fraction allowing obtaining a flow rich in nitrogen and methane in the head.

[0069] The fractioning medium (110) is preferably provided with a mesh to limit the entrainment of droplets in the gas fraction.

[0070] This reflux drum 111 is connected to the outlet of the light fraction of the means (110) for fractionation, with or without intermediate exchange in the first body 115, and operates in a similar way separating the light fraction from the heavy fraction residues carried unexpectedly by the light fraction out of the means (110) for fractionation.

[0071] Drum 111 is preferably equipped with a

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19/39 mesh to limit the entrainment of droplets in the gas fraction.

[0072] The light fraction that leaves the fractionation means 110, or the reflux drum 111 when that drum 111 is present, is preferably compressed by a second compressor 112.

[0073] The second compressor 112 is, for example, a

compressor centrifugal. This one compressor centrifuge is in preference triggered through the turbine implemented at the compressor 105 when the compressor 105 it's a compressor centrifugal. [0074] A pressure on exit of the second compressor 112 is,

for example, on the order of 40 bar (4 MPa) absolute and the compression ratio is preferably between 2 and 4.

[0075] The light fraction, with or without compression in the second compressor 112, is preferably cooled in a sixth heat exchanger 113.

[007 6] This heat exchanger 113 is, for example, a tubular exchanger in which the cold source is air or water. The colder the source, the greater the cooling efficiency. Preferably, the maximum cooling temperature corresponds to the air or water temperature plus fifteen degrees Celsius. The resulting flow brings cold or not

heating necessary for cooling from gas s natural. [0077] A light fraction, compressed or not in the second compressor 112, cooled or not at the sixth exchanger in heat 113, is transmitted to first exchanger in heat 115. [0078] 0 first exchanger in heat 115 is, per example, a exchanger coiled heat in the what fraction

light acts as a cold source and natural gas as a

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20/39 hot source. Preferably, the first exchanger 115 and the second exchanger 120 are formed by a single spiral exchanger.

[0079] Natural gas enters the first exchanger 115 through inlet 116.

[0080] The light fraction vaporized during the exchange with natural gas in the first exchanger body 115 is preferably redirected to a drum 114 configured to separate the light fraction into two parts, one being heavier than the other.

[0081] The device 100 preferably comprises a valve 136 upstream of the drum 114. This valve creates, for example, an expansion of the gas portion of the first mixture in the order of 20 to 25 bar (2 to 2.5 MPa ).

[0082] The two parts of the light fraction are transmitted to the second exchange body 120, the light fraction acting as a cold source in the heat exchange made with the natural gas previously cooled in the first exchange body 115.

[0083] When the device 100 employs a drum 114, the heavy part of the light fraction is, after passing through the second exchanger body 120, expanded in an expander 118, then transmitted to the compressor 105 through the return line 125.

[0084] This expander 118 is placed in place of a valve 123 or in parallel with this valve 123.

[0085] In the modalities, between the expander 118 and the compressor 105, the heavy part of the light fraction, compressed, is reinjected in the second exchanger body 120.

[0086] The light portion of the light fraction is transmitted to

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21/39 the compressor 105 through the return line 125.

[0087] In the modalities, the light part of the light fraction, after leaving the second exchange body 120, is expanded into a valve 122, and is reinjected into the second exchange body 120 before being redirected to the compressor 105.

[0088] The valve 122 creates an expansion to reach a pressure of about 4 to 5 bar (0.4 to 0.5 MPa), as a function of the pressure drop of the downstream circuit, for example.

[0089] The heavy fraction of the refrigerant mixture that leaves the medium (110) for fractionation is passed to the first exchanger body 115 and acts as a heat sink when exchanging with natural gas.

[0090] In the embodiments, the device 100 comprises an expander 127 in parallel with a valve 122.

[0091] Preferably, the device 100 comprises an expander 127 and does not comprise a valve 122.

[0092] In the modalities, the heavy fraction leaves the first exchange body 115 and is reinjected into this first exchange body 115, after being expanded in a regulator 119, before being redirected to compressor 105.

[0093] Regulator 119 creates an expansion to reach a pressure of about 4 to 5 bar (0.4 to 0.5 MPa), as a function of the pressure drop in the first exchanger body 115, for example.

[0094] In the embodiments, the return line 125 comprises a drum 126 between the first exchanger body 115 and the compressor 105.

[0095] This drum 126 ensures that at the entrance of the first compressor 105, the first refrigerant mixture

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22/39 is exclusively in gaseous form.

[0096] Drum 126 is preferably provided with a mesh to limit the entrainment of droplets in the gas fraction.

[0097] Preferably, device 100 comprises a conduit that connects a part of drum 126, intended to receive the liquid portion of the first mixture, by means (110) for fractionation. This duct is preferably provided with a pump. Preferably, this pump is activated as a function of a level of liquid captured by a sensor in the portion of the drum 126 intended to receive the liquid portion of the first mixture.

[0098] Thus, as understood, natural gas is liquefied through two successive cooling stages. The first step occurs in the first exchange body 115 and the second step occurs in the second exchange body 120.

[0099] Natural gas flows in the first body 115 and in the second body 120, preferably against the current of the first refrigerant mixture.

[00100] The cooled natural gas preferably leaves the first body 115 at a temperature of about -30 ° C. This cooled natural gas is then preferably directed to a fractionation section (not shown) to separate any condensates from the gas fraction. The gas fraction is transmitted to the second body 120 to be liquefied.

[00101] In addition to these two stages, the present invention proposes the addition of a third cooling stage positioned both before and after the first two stages.

[00102] In the first case, a third exchanger body

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130 is positioned upstream of the natural gas inlet 116 in the first exchange body 115. This third exchange body 130 is, for example, a tubular exchanger that uses, as a cold source, a second refrigerant compound, and natural gas from the hot source that enters on device 100 to be liquefied.

[00103] The second chemical compound is, for example, a pure substance composed of nitrogen, propane and / or ammonia or a mixture of nitrogen and propane.

[00104] Preferably, when ammonia is used, this ammonia is used alone.

[00105] In the second case, a third exchange body 135 is positioned downstream of the liquefied natural gas outlet 121 of the second exchange body 120. This third exchange body 135 is, for example, a tubular exchanger that uses, as a cold source, a second refrigerant compound and a hot source of liquefied natural gas that leaves device 100 for storage or consumption. The natural gas thus liquefied can be expanded at atmospheric pressure by a regulator (not shown) before storage. The evaporation gas, called BOG (Boil-off gas), collected in the storage of liquefied natural gas can be reinjected into device 100 in the gas fraction, leaving the fractionation section between the first exchanger body 115 and the second exchanger body 120.

[00106] The second refrigerant compound in this document is, for example, liquid nitrogen.

[00107] Downstream of this third body, 130 or 135, the device 100 comprises a means, 140 or 145, for compressing the second compound.

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[00108] This one compressor, 140 or 145 is, for example, one compressor centrifugal. [00109] In some modalities preferred, O device 100 comprises The stage in cooling The

upstream and downstream cooling step.

[00110] In these embodiments, the third exchange body 130 is called the exchange body positioned upstream of the first exchange body 115 and the fourth exchange body 135 is called the exchange body positioned downstream of the second body 120. The second refrigerant compound is called the mixture refrigerant used in the third body 130 and the third mixture cools the designated refrigerant mixture used in the fourth exchanger body.

[00111] In the modalities, the device 100 comprises:

- the means 150 for cooling the second compressed compound in the compression means 140 and

- a conduit 155 for transferring the second compressed compound to the third exchange body 130.

[00112] Cooling medium 150 is, for example, a heat exchanger between the second vaporized compound during the heat exchange with natural gas in the third exchanger body 130 and air or water.

[00113] In some embodiments, such as that shown in figure 1, the device 100 comprises, between an outlet 131 for the second compound, the means 150 for cooling the second compound and the third exchange body 130, a circuit 170 for cooling the second compound with the heavy fraction of the first mixture within the first exchange body 115.

[00114] This 170 cooling circuit is produced,

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25/39 for example, by entering the second cooled compound into the first exchange body 115, the second cooled compound acting as a hot source in relation to the heavy fraction and any light fraction that passes through this first exchange body 115. This second vaporized compound can act simultaneously as a cold source in relation to the entry of natural gas into the first body 115 through the entry 116 for natural gas.

[00115] In the modalities, the second vaporized compound that leaves the first body 115, is expanded in regulator 124, being then reinjected into the first body 115 or the second body 120.

[00116] The second compound is expanded, for example, at a pressure between 3 and 4 bars (0.3 to 0.4 MPa), depending on the pressure drop in the upstream coducts.

[00117] The purpose of this cooling circuit 170 is to facilitate the cooling that occurs in the cooling means 150.

[00118] In the modalities, as shown in Figure 1, a part of the cooling circuit 170 is configured to cool the second compound by heat exchange with the light fraction of the first mixture in the second exchanger body 120.

[00119] In these modalities, the second compound, cooled by heat exchange in the first exchange body 115, is injected into the second exchange body 120. The second vaporized compound then acts as a hot source in relation to the light fraction of the first refrigerant mixture that passes through this second exchanger body 120. At the same time, this second vaporized compound can work,

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26/39 simultaneously, as a cold source in relation to the natural gas introduced in the second exchanger body 120.

[00120] In some embodiments, device 100 comprises:

- the means 160 for cooling nitrogen and

- a conduit 165 for transporting the cooled nitrogen to the fourth exchanger body 135.

[00121] Cooling medium 160 is, for example, a heat exchanger between the third compressed mixture and air or water.

[00122] Natural gas can be pretreated before the third exchanger body 130.

[00123] The compressors and compression means, 105, 112 and 140 used in this modality can be replaced by compressors, 605, 610 and 620, described with reference to Figure 6 and whose functions are similar.

[00124] Figure 2, which is not to scale, shows a schematic view of a modality of vessel 200, which is the object of the present invention. This vessel 200 comprises:

- a device 100 for liquefying a natural gas as described with reference to figure 1,

- a device 400 for liquefying a natural gas as described with reference to figure 4, or

- a device 600 for liquefying a natural gas as described with reference to figure 6.

[00125] Figure 3 shows, schematically and in the form of a logical diagram, a particular sequence of steps of method 300, which is the object of the present invention. This method 300 for liquefying a natural gas, comprises:

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- a step 305 for compressing a first vaporized refrigerant chemical mixture,

- a step 310 to fractionate the compressed mixture into a heavy fraction and a light fraction,

- a first stage of heat exchange 315 between the heavy fraction of the first mixture and natural gas, in order to cool at least natural gas,

- a second heat exchange step 320 between the light fraction of the first mixture and the cooled natural gas during the first exchange step for liquefying the natural gas, and

- a return step 325 of the first vaporized refrigerant mixture in the heat exchange bodies for the compression step, which comprises:

- before the entry of natural gas from the first exchange stage or after the exit of liquefied natural gas from the second exchange stage, a third heat exchange stage 330 between natural gas and a second chemical compound refrigerant, and

- a step 335 of compressing the second vaporized compound.

[00126] This method 300 is carried out, for example, by using the device 100 as described with reference to figure 1. As will be understood, all the variants, all the examples and all the modalities of the device 100 can also be transposed as steps within method 300.

[00127] Figure 4, which is not to scale, shows a schematic view of an embodiment of device 400 which is the subject of the present invention. That

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28/39 device 400 for liquefying a natural gas, comprises:

- a compressor 105 of a first vaporized refrigerant chemical mixture,

- the means 110 for fractionating the compressed mixture into a heavy fraction and a light fraction,

- a first heat exchanger body 115 between the heavy fraction of the first mixture and the natural gas intended to cool at least the natural gas;

- a second heat exchanger body 120 between the light fraction of the first mixture and the cooled natural gas in the first heat exchanger body for liquefying the natural gas, and

- a conduit 125 for returning the first vaporized refrigerant mixture in the heat exchange bodies to the compressor, comprising:

- a 405 regulator for liquefied natural gas,

- an evaporator gas collector 410 produced during the expansion of gas in regulator 405, and

- a conduit 415 for injection of evaporation gas at the entrance of the second exchanger body.

[00128] In this figure 4, the various means related to the first refrigerant mixture are identical to the means described with reference to figures 1 or 6, including the modalities and the particular variants described with reference to figures 1 and 6. These means are:

- compressor 105,

- exchanger 106,

- the fractionation medium 110,

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- the reflux drum 111,

- compressor 112,

- exchanger 113,

- drum 114,

- the first exchanger body 115,

- inlet 116 for natural gas,

- expander 118,

- regulator 119,

- the second exchanger body 120,

- outlet 121 for liquefied natural gas from second exchange body 120,

- regulator 122,

- expander 126,

- the return line 125

- drum 126, and

- valve 136.

[00129] In this way, as can be understood, natural gas is liquefied through two successive cooling stages. The first step occurs in the first exchange body 115 and the second step occurs in the second exchange body 120.

[00130] Between these two stages, that is, between an outlet (unnumbered) for the cooled natural gas of the first body 115 and an inlet (unnumbered) for the cooled natural gas in the second body 120, the device 400 comprises, preferably, a fractionation section configured to remove condensate from the gas stream.

[00131] The liquefied natural gas that leaves the second body 120 through outlet 121 passes through a regulator 405 configured to expand the natural gas

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liquefied The atmospheric pressure. [00132] 0 regulator 405 is therefore example, an valve what implements O Joule-Thomson effect. [00133] This expansion causes appearance of the gas in evaporation, or BOG. [00134] 0 BOG thus generated is collected in one collector 410 and injected r through a conduit 415, at input of

second exchanger body 120. This injection can occur upstream, in or downstream of the fractionation section, if such a section is present.

[00135] The collector is, for example, a gas / liquid separation drum 410 equipped with a mesh to limit the drag of droplets in the gas fraction.

[00136] Preferably, the conduit 415 is equipped with a compressor 416 that compresses the gas fraction that leaves the collector 410.

[00137] In some embodiments, such as that illustrated in figure 4, a third exchange body 420 is positioned upstream of inlet 116 for natural gas in the first exchange body 115. This third exchange body 420 is, for example, a tubular exchanger which uses, as a cold source, a second refrigerant compound, and natural gas from a hot source that enters the device 400 to be liquefied.

[00138] The device 400 then comprises a compressor 425 of the second vaporized compound downstream of the third exchange body 420. This compressor 425 is, for example, a centrifugal compressor.

[00139] The second chemical compound is, for example, a pure substance comprising nitrogen, propane and / or

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31/39 ammonia or a mixture of nitrogen and propane.

[00140] In some embodiments, device 400 includes:

- a means 430 for cooling the second compressed compound, and

- a transfer duct 435 of the second cooled compound to the third exchange body 420.

[00141] Cooling medium 430 is, for example, a heat exchanger between the second compressed compound and water or glycol.

[00142] In some embodiments, such as that shown in figure 4, the device 400 comprises, between an outlet 421 for the second compound of the means 430 for cooling the second compound and the third exchange body 420, a cooling circuit 440 for the second compound of the heavy fraction, of the first mixture, within the first exchanger body 115.

[00143] This cooling circuit 440 is obtained, for example, by entering the second cooled compound in the first exchanger body 115, the second cooled compound acting as a hot source in relation to the heavy fraction and any light fraction that crosses that first exchanger body 115. At the same time, this second cooled compound can simultaneously act as a cold source in relation to the natural gas that enters the first body 115 through inlet 116 for natural gas.

[00144] In some embodiments, the second vaporized compound that leaves the first body 115, is expanded in a regulator 424 and is reinjected into the first body 115 or the second body 120.

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32/39 [00145] The second compound is expanded, for example, at a pressure of 3 to 4 bars (0.3 to 0.4 MPa) at the outlet of regulator 424.

[00146] This 440 cooling circuit is intended to facilitate the cooling that occurs in the cooling media 430.

[00147] This circuit 440 may also include a second part, in the second exchanger body 120, as described with reference to figure 1.

[00148] In some particular modalities, the first refrigerant mixture comprises nitrogen and methane and at least one of:

- ethylene,

- ethane,

- propane and / or

- butane.

[00149] Figure 5 shows schematically a particular modality of the method that is the object of the present invention. This 500 method for liquefying a natural gas, comprises:

- a step 505 for compressing a first vaporized refrigerant chemical mixture,

- a 510 step to fractionate the compressed mixture into a heavy fraction and a light fraction,

- a first stage of heat exchange 515 between the heavy fraction of the first mixture and natural gas to cool at least natural gas,

- a second heat exchange step 520 between the light fraction of the first mixture and the cooled natural gas during the first exchange step for gas liquefaction

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33/39 natural and

- a step 525 of returning the first refrigerant mixture vaporized in the heat exchange bodies for the compression step, comprises:

- a 530 step to expand liquefied natural gas,

- a 535 stage for collecting the evaporation gas produced during the expansion stage, and

- an evaporation gas injection step 540 at the entrance of the second exchanger body.

[00150] This method 500 is performed, for example, by using the device 400 as described with reference to figure 4. As will be understood, all the variants, all the examples and all the modalities of the device 400 can also be transposed with the steps within method 500.

[00151] Figures 6 and 7 show, schematically, a particular embodiment of the device 600, which is the object of the present invention. This device 600 for liquefying a natural gas, comprises:

- a first 605 centrifugal compressor from a first vaporized refrigerant chemical mixture,

- the means (110) for fractionating the compressed mixture into a heavy fraction and a light fraction,

- a second 610 light-weight centrifugal compressor,

- a first heat exchanger body 115 between the heavy fraction of the first mixture and the natural gas intended to cool at least the natural gas;

- a second heat exchanger body 120 between the light compressed fraction of the first mixture and the natural gas cooled in the first heat exchanger body for liquefaction of the

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34/39 natural gas, and

- a return line 125 of the first refrigerant mixture vaporized in the heat exchange bodies for the first compressor, comprising:

- upstream of a natural gas inlet 116 in the first exchanger body, a third body 420 for heat exchange between natural gas and a second refrigerant chemical compound,

- a third centrifugal compressor 620 of the second vaporized compound, the first and third centrifugal compressors being driven by a single turbine in common 630,

- a housing 635 common to the first compressor and the third compressor,

- a means 430 for cooling the second compressed compound, and

- a conduit 435 for transferring the second cooled compound to the third exchange body 420.

[00152] The term enclosure, refers to an enclosure that comprises at least one compressor. Each compressor has one or more wheels.

[00153] In this figure 6:

- exchanger 106,

- the medium 110 for fractionation,

- the reflux drum 111,

- exchanger 113,

- the first exchanger body 115,

- entry 116 for natural gas,

- regulator 119,

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- the second exchanger body 120,

- outlet 121 for liquefied natural gas from second exchange body 120,

- regulator 122,

- expander 127,

- return line 125,

- drum 126,

- valve 136,

- the third exchange body 420,

- the transfer line 435,

- the fourth exchanger body 430,

- outlet 421 for the second refrigerant compound,

- the cooling circuit 400,

- regulator 424,

- regulator 405,

- the collector 410 and

- the injection duct 415, are identical to the corresponding means described with reference to Figures 1 or 4, including the particular modalities and variants described with reference to these Figures 1 and 4.

[00154] The third compressor 620 corresponds to the third compressor 140 as described with reference to figure 1. However, this third compressor 620 is driven by the use of a single turbine in common with the turbine that operates the first compressor 605. The first compressor corresponds to first compressor 105, as described with reference to figure 1.

[00155] The fourth compressor 615 is configured to increase the pressure of the light portion of the light fraction of the

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36/39 first cooling mix. This fourth compressor shares a single turbine common with the second compressor 610, this second compressor 610 corresponds to the second compressor 112, as described, with reference to figure 1.

[00156] In preferred embodiments, such as that shown in figures 6 and 7, turbine 630 that operates the first and third compressors, 605 and 620, and turbine 640 that drives the second and fourth compressors, 610 and 615, are mechanically coupled.

[00157] This coupling is obtained, for example, by using any type of rotation axis coupling

known to knowledgeable in the technique. [00158] On some modalities preferred, such how at shown in Figures 6 and 7, the 630 turbines and 640 are combined. [00159] On some modalities preferred, such how at represented in figures 6 and 7, the device 600, what it's the

object of the present invention, comprises:

- between the second compressor 610 and the second exchanger body 120, a fourth centrifugal compressor 615 of the light fraction of the first mixture, the second and fourth centrifugal compressors being driven by a single common turbine 640, and

- a 645 housing common to the second compressor and the fourth compressor.

[00160] In some preferred embodiments, such as that shown in figure 6, the device 600 that the object of the present invention comprises:

- a separator 650 of a gas fraction and a liquid fraction of the compressed light stage, the fourth compressor 615

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37/39 by compressing the separate gas fraction,

- a 625 regulator of the liquid fraction of the heated light stage in the second exchanger body,

- the turbine 640 of the fourth compressor being driven by the expansion energy.

[00161] The separator 650, for example, is similar to the reflux drum 114 as described with reference to the figure

1. Regulator 625 is, for example, similar to expander 118 as described with reference to figure 1.

[00162] In the preferred embodiments, such as that shown in Figure 6, the second chemical compound comprises nitrogen, propane and / or ammonium.

[00163] In the preferred embodiments, such as that shown in Figure 6, the first refrigerant mixture comprises nitrogen and methane and at least one of:

- ethylene,

- ethane,

- propane and / or

- butane.

[00164] In preferred embodiments, such as those shown in figure 6, device 600 comprises:

- a 405 regulator of liquefied natural gas,

- an evaporator gas collector 410 produced during the expansion of the gas in the regulator and

- a conduit 415 for injection of evaporation gas at the entrance of the second exchanger body.

[00165] In preferred embodiments, such as that shown in Figure 6, device 600 comprises, between an outlet 421 for the second compound of the cooling means 430 and the third exchange body 420, a circuit 440 for

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38/39 to cool the second compound by the heavy fraction of the first mixture within the first exchanger body 115.

[00166] In some preferred embodiments, such as those shown in figure 6, the first exchanger body 115 and / or the second exchanger body 120 is a coiled heat exchanger.

[00167] In some preferred modalities, such as

shown in figure 6 , O middle 430 for cooling of second compound is a exchanger of heat in between the second compound and the water. [00168] The figure 8 show schematically an modality particular of method 700 that it's the object gives

present invention. This method 700 is intended for the liquefaction of a natural gas comprising:

- a step 705 of centrifugal compression of a first vaporized refrigerant chemical mixture,

- a step 710 of fractionating the compressed mixture into a heavy fraction and a light fraction,

- a second stage 715 of centrifugal compression of the light fraction,

- a first stage 720 of heat exchange between the heavy fraction of the first mixture and natural gas to cool at least natural gas,

- a second heat exchange step 725 between the light compressed fraction of the first mixture and the cooled natural gas in the first exchange body for liquefying the natural gas, and

- a step 730 of returning the first vaporized refrigerant mixture during the heat exchange steps to the first compression step,

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39/39 comprises:

- upstream of a step 7 35 to enter natural gas in the first exchange step, a third step 740 of heat exchange between natural gas and a second refrigerant chemical compound,

- a third stage 745 of centrifugal compression of the second vaporized compound, the first and third stages of centrifugal compression being driven by a single turbine in common,

- the first and third stages of compression being performed in a common enclosure,

- a step 750 of cooling the second compressed compound during the third exchange step,

- a step 755 for transferring the second cooled compound to the third exchange step,

- between the second stage of compression and the second stage of exchange, a fourth stage 760 of centrifugal compression of the light fraction of the first mixture, the second and fourth stages of centrifugal compression being driven by a single common turbine, and

- a first and third compression steps being carried out in a common enclosure.

[00169] This method 700 is carried out, for example, by the implementation of device 600, as described, with reference to figures 6 and 7. As will be understood, all variants, all examples and all modalities of device 600 can also be transposed as steps within method 700.

Claims (11)

1. Device (600) for liquefying a natural gas comprising: - a first centrifugal compressor (605) of a first chemical mixture of vaporized refrigerant, - a means (110) for fractionating the compressed mixture into a heavy fraction and a light fraction, - a second centrifugal compressor (610) of the light fraction, - a first body (115) to exchange heat between the heavy fraction of the first mixture and natural gas to cool at least natural gas, - a second body (120) for exchanging heat between the light compressed fraction of the first mixture and the cooled natural gas in the first exchanger body for liquefying the natural gas, and - a conduit (125) for returning the first vaporized refrigerant mixture in the heat exchange bodies to the first compressor, characterized by the fact that it comprises: - upstream of a natural gas inlet (116) in the first exchanger body, a third body (420) to exchange heat between natural gas and a second refrigerant chemical compound, - a third centrifugal compressor (620) of the second vaporized compound, in which the first and third centrifugal compressors are driven by a single turbine in common (630), - a housing (635) common to the first compressor and the third compressor, Petition 870190057764, of 06/24/2019, p. 15/20 2/5 - medium (430) for cooling the second compressed compound, - a conduit (435) for transferring the second cooled compound to the third exchange body, - between the second compressor (610) and the second exchanger body (120), the fourth centrifugal compressor (615) of the light fraction of the first mixture, the second and fourth centrifugal compressors being driven by a single turbine in common (640), and - a housing (645) common to the second compressor and the fourth compressor. 2. Device (600) according to claim 1, characterized by the fact that the turbine (630) which operates the first and third compressors (605, 620) and the turbine (640) which operates the second and fourth compressors (610, 615) are mechanically coupled. 3. Device (600) according to claim 2, characterized by the fact that the turbines (630, 640) are combined. Device (600) according to any one of claims 1 to 3, characterized in that it comprises: - a separator (650) of a gas fraction and a liquid fraction of the compressed light phase, the fourth compressor (615) compressing the separated gas fraction, - a regulator (625) for the liquid fraction of the heated light phase in the second exchanger body, - the turbine (640) of the fourth compressor being driven by the expansion energy. 5. Device (600), according to any Petition 870190057764, of 06/24/2019, p. 16/20 3/5 of claims 1 to 4, characterized in that the second chemical compound comprises a pure substance comprising nitrogen, propane and / or ammonia. 6. Device (600) according to any one of claims 1 to 5, characterized by the fact that the first refrigerant mixture comprises nitrogen and methane and at least one of: - ethylene, - ethane, - propane; and / or - butane. Device (600) according to any one of claims 1 to 6, characterized by the fact that it comprises: - a regulator (405) for liquefied natural gas, - a collector (410) for the evaporation gas produced during the expansion of the gas in the regulator; and - a conduit (415) for injection of the evaporation gas at the entrance of the second exchanger body. Device (600) according to any one of claims 1 to 7, characterized in that the means for cooling the second compound comprise an outlet (421) for the second compound, the device comprising, between said outlet and the third exchange body (420), a circuit (440) for cooling the second compound with the heavy fraction of the first mixture inside the first exchange body (115). Device (600) according to any one of claims 1 to 8, characterized in that the first exchanger body (115) and / or the second body Petition 870190057764, of 06/24/2019, p. 17/20 4/5 exchanger (120) constitute a spiral exchanger. Device (600) according to any one of claims 1 to 9, characterized by the fact that the means (430) for cooling the second compound constitutes a heat exchanger between the second compound and water. 11. Method (700) for liquefying a natural gas comprising: - a first stage (705) of centrifugal compression of a first chemical mixture of vaporized refrigerant, - a step (710) of fractionating the compressed mixture into a heavy fraction and a light fraction, - a second stage (715) of centrifugal compression of the light fraction, - a first stage (720) of heat exchange between the heavy fraction of the first mixture and natural gas to cool at least natural gas, - a second stage (725) of heat exchange between the light fraction of the first mixture and the cooled natural gas in the first exchanger body for liquefying the natural gas, and - a return step (730) of the first vaporized refrigerant mixture during the heat exchange steps for the first compression step, characterized by the fact that it comprises: - upstream of a step (735) of entry of natural gas in the first exchange step, a third step (740) of heat exchange between natural gas and a second refrigerant chemical compound - a third stage (745) of centrifugal compression of the second vaporized compound, the first and third being Petition 870190057764, of 06/24/2019, p. 18/20 5/5 centrifugal compression steps driven by a single turbine in common, - the first and third stages of compression being carried out in a common enclosure, - a step (750) for cooling the second compressed compound during the third exchange step, - a step (755) of transferring the second cooled compound to the third exchange step, - between the second stage of compression and the second stage of exchange, a fourth stage (760) of centrifugal compression of the light fraction of the first mixture, the second and fourth stages of compression being driven by a single turbine in common, and - the first and third stages of compression being carried out in a common enclosure.