FR3068772A1 - DEVICE AND METHOD FOR LIQUEFACTING NATURAL GAS OR BIOGAS - Google Patents

Abstract

The method (300) for liquefying a natural gas or a biogas comprises: a first compression step (320) of vaporized carbon dioxide; a first heat exchange step (325) for cooling the dioxide; of compressed carbon, - a first heat exchange step (330) between the gas, the cooled carbon dioxide and the expanded carbon dioxide during a step (335) of expansion of the cooled carbon dioxide, - step (335) of expanding the carbon dioxide cooled during the first heat exchange step (330), the expanded carbon dioxide being supplied to the first heat exchange step (330), - a second step a refrigerant (305) for compressing a refrigerant fluid, a second cooling heat exchange (310) stage for the compressed refrigerant fluid, a second heat exchange stage (360) for the gas, the cooled refrigerant fluid, and the coolant relaxed during a period pe (315) of expansion of the cooled refrigerant, - the means (315) of expansion of the coolant cooled during the second heat exchange step (360), the expanded coolant being supplied to the second step of heat exchange.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and a method for liquefying a natural gas or a biogas. It applies, in particular, to the field of liquefied natural gas, the liquefaction of natural gas, the transport of natural gas, biogas and the field of liquefaction of evaporative gas.

STATE OF THE ART

Gas liquefaction allows the transport of natural gas at a lower volume compared to the transport of non-liquefied natural gas.

In recent decades, liquefaction technologies have targeted large gas capacities for reasons of economy of scale.

The implementation of the technologies thus used requires very large investments and presents very significant transport costs (marine liquefaction and reception infrastructures). On the one hand, the trend in liquefaction capacity has been to increase the volume of natural gas transported in order to obtain economies of scale and to make the economy of these projects more attractive. On the other hand, the investments made to implement these technologies have targeted this design and the construction of liquefaction processes which must be as efficient as possible in order to minimize operating costs thereafter.

Today, the number of large-scale projects has sharply decreased and there is a renewed interest in the production of small-capacity liquefied natural gas from natural gas or biogas.

Indeed, the development of small sources of gas, fatal gases and biogas are new opportunities promoted in particular by an environmental awareness of populations and governments or a desire to reach an isolated consumer in areas without gas transport infrastructure and / or distribution. These opportunities are nevertheless too small to justify the use of technologies intended for large-scale production (the transposition of traditional technologies is not relevant, as it is too complex and does not justify the economic viability of these new projects) , hence the need to propose new technologies that can meet the three main challenges concerning small-scale liquefaction:

- reducing investment costs as much as possible while keeping efficiency as high as possible in order to minimize operational costs,

- increasing the efficiency of the process to minimize product loss: the volumes of gas to be recovered are low, which makes each molecule important and

- the reduction of health, environmental and security risks due to the proximity of these technologies closer to urban areas and the reduction of the environmental footprint of these technologies.

Three types of liquefaction processes are known:

- closed cycle processes with phase change of the refrigerant, the latter being either a pure body or a refrigerant mixture in order to improve efficiency,

- Brayton closed cycle or expansion (expansion cycle) processes in which the refrigerant remains in the gaseous state and

- open cycle processes, in which the cold is not created but supplied by an external medium, typically liquid nitrogen, and where the liquefaction of natural gas results from a simple heat exchange with the cold medium which vaporizes; this type of process is generally used in laboratories or in very specific applications requiring very little performance and a lot of simplicity.

Closed cycle processes with phase change have the disadvantages of requiring significant capital investments, of being complex in their implementation and of requiring bulky equipment.

Brayton’s processes have the disadvantages of having average to low energy performance, requiring capital investment and significant operating costs, and requiring bulky equipment.

Open cycle processes have the disadvantages of having a low energy performance and a high cost of energy supply.

OBJECT OF THE INVENTION

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

To remedy all or part of these drawbacks, the present invention provides a method and a device having as a general principle the cooling by successive heat exchanges between natural gas or biogas with refrigerating bodies or mixtures. In this way, the temperature of the biogas or natural gas is gradually lowered until the liquefaction of said biogas or natural gas.

Preferably, this cooling includes a pre-cooling by heat exchange between natural gas or biogas and a pure cooled refrigerant.

At a minimum, this cooling includes a heat exchange between natural gas or biogas and cooled carbon dioxide. This cooling is preferably carried out after the pre-cooling step.

The method and the device which are the subject of the present invention comprise an additional cooling step, downstream of the cooling step, between the natural gas or the biogas and a cooled refrigerant.

Thus, according to a first aspect, the present invention relates to a device for liquefying a natural gas or a biogas, which comprises:

- a first vaporized carbon dioxide compressor,

- a first heat exchanger for cooling the compressed carbon dioxide,

- a first heat exchange body between:

- the gas and the cooled carbon dioxide, the cooled carbon dioxide being supplied to a means of expansion of the carbon dioxide,

the expanded gas and carbon dioxide, at the outlet of the means for expanding the carbon dioxide, the vaporized carbon dioxide being supplied to the first compressor, and

- expanded carbon dioxide and cooled carbon dioxide,

the means for expanding the cooled carbon dioxide in the first exchange body, the expanded carbon dioxide being supplied to the first exchange body,

- a second compressor of a refrigerant,

- a second heat exchanger for cooling the compressed refrigerant,

- a second heat exchange body between:

- the gas leaving the first exchange body and the cooled refrigerant, the cooled refrigerant being supplied to a means of expansion of the refrigerant,

the gas leaving the first exchange body and the expanded coolant, at the outlet of the expansion means of the coolant, the vaporized coolant being supplied to the second compressor and

- the expanded refrigerant and the cooled refrigerant,

- The means of expansion of the cooled refrigerant in the second exchange body, the expanded refrigerant being supplied to the second exchange body.

Thanks to these provisions, the device which is the subject of the present invention:

- does not require the presence of heavy hydrocarbons in the refrigerant mixtures, which can cause problems / risks of crystallization in the first heat exchange body,

- uses a reduced number of different chemical compounds as a refrigerant and

- minimizes refrigerant circulation rates.

In addition, the use of carbon dioxide as a refrigerant allows:

- reduce the flow rate of the refrigerant cycle and therefore the size of the compressor required in comparison with a process not using carbon dioxide as a refrigerant (for example nitrogen gas) and

- to reduce the number of chemical compounds used in the refrigerant mixture by eliminating the use of propane-type compounds and heavier hydrocarbons potentially crystallizable for the liquefaction of the gas.

In embodiments, the refrigerant leaving the second heat exchanger is supplied to the first exchange body, the refrigerant being cooled by heat exchange with carbon dioxide in the first exchange body, the refrigerant being outlet of the first exchange body being supplied to the second exchange body.

These embodiments make it possible to cool the refrigerant and gain energy efficiency.

In embodiments, the device which is the subject of the present invention comprises:

- a third compressor of a pure vaporized refrigerant,

a third heat exchanger for cooling the compressed refrigerant compound,

- a third heat exchange body between:

the expanded coolant and the coolant to cool the coolant, the coolant being supplied to a means of expansion of the coolant,

- the gas and the refrigerant expanded to cool the gas, the vaporized refrigerant being supplied to the third compressor and the cooled gas being supplied to the first heat exchange body and

- The means of expansion of the cooled refrigerant in the third exchange body, the expanded refrigerant being supplied to the third exchange body.

These embodiments allow the gas to be precooled before this gas passes through the first heat exchange body.

In embodiments, the coolant leaving the second heat exchanger is supplied to the third exchange body, the coolant being cooled by heat exchange with the coolant in the third exchange body, the coolant leaving the third exchange body being supplied to the first exchange body.

These embodiments make it possible to cool the refrigerant and gain energy efficiency.

In embodiments, the device which is the subject of the present invention comprises a fourth heat exchange body between the expanded refrigerant compound at the outlet of the expansion means and the carbon dioxide cooled at the outlet of the heat exchanger for cooling the dioxide. of carbon.

These embodiments allow greater cooling of the carbon dioxide upstream of the heat exchange between the carbon dioxide and the gas.

In embodiments, the pure refrigerant compound is ammonia or propane.

These embodiments minimize the use of explosive compounds.

In embodiments, the refrigerant mixture includes nitrogen and / or methane.

These embodiments limit the use of explosive compounds.

According to a second aspect, the present invention relates to a process for liquefying a natural gas or a biogas, which comprises:

- a first stage of compression of vaporized carbon dioxide,

- a first stage of heat exchange to cool the compressed carbon dioxide,

- a first stage of heat exchange between:

the gas and the cooled carbon dioxide, the cooled carbon dioxide being supplied at a stage of expansion of the carbon dioxide,

- the expanded gas and carbon dioxide, at the outlet of the expansion step of carbon dioxide, the vaporized carbon dioxide being supplied in the first compression step and

- expanded carbon dioxide and cooled carbon dioxide,

- the expansion step of the carbon dioxide cooled during the first heat exchange step, the expanded carbon dioxide being supplied in the first heat exchange step,

- a second stage of compression of a refrigerant,

- a second stage of heat exchange for cooling the compressed refrigerant,

- a second stage of heat exchange between:

- the gas leaving the first exchange stage and the cooled refrigerant, the cooled refrigerant being supplied at a stage of expansion of the refrigerant,

the gas leaving the first exchange stage and the expanded refrigerant, at the outlet of the expansion step of the refrigerant, the vaporized refrigerant being supplied in the second compression stage and

- the expanded refrigerant and the cooled refrigerant,

- the expansion step of the coolant cooled during the second heat exchange step, the expanded coolant being supplied in the second heat exchange step.

In embodiments, the refrigerant leaving the second heat exchange stage is supplied to the first exchange stage, the refrigerant being cooled by heat exchange with carbon dioxide during the first stage d heat exchange, the refrigerant leaving the first exchange step being supplied to the second exchange step.

In embodiments, the method which is the subject of the present invention comprises:

- a third stage of compression of a pure vaporized refrigerant,

- a third stage of heat exchange for cooling the compressed refrigerant,

- a third stage of heat exchange between:

the expanded coolant and the coolant to cool the coolant, the coolant being supplied to a step of relaxing the coolant,

- the gas and the refrigerant expanded to cool the gas, the vaporized refrigerant being supplied in the third compression step and the cooled gas being supplied in the first heat exchange step and

the expansion step of the refrigerant compound cooled during the third exchange step, the expanded refrigerant being supplied in the third exchange step.

In embodiments, the refrigerant leaving the second heat exchange stage is supplied to the third exchange stage, the refrigerant being cooled by heat exchange with the refrigerant during the third stage of heat exchange, the refrigerant leaving the third exchange step being supplied to the first exchange step.

In embodiments, the method which is the subject of the present invention comprises a fourth stage of heat exchange between the expanded refrigerant compound at the outlet of the expansion stage and the carbon dioxide cooled at the outlet of the exchange stage thermal cooling of carbon dioxide.

The aims, advantages and particular characteristics of the method which is the subject of the present invention being similar to those of the device which is the subject of the present invention, they are not repeated here.

BRIEF DESCRIPTION OF THE FIGURES

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

FIG. 1 schematically represents a first particular embodiment of the device which is the subject of the present invention,

FIG. 2 schematically represents a particular embodiment of a boat comprising a device which is the subject of the present invention,

FIG. 3 represents, diagrammatically and in the form of a flowchart, a succession of particular steps of the method which is the subject of the present invention,

FIG. 4 schematically represents a second particular embodiment of the device which is the subject of the present invention, and

- Figure 5 shows, schematically, a third particular embodiment of the device object of the present invention.

DESCRIPTION OF EXAMPLES OF EMBODIMENT OF THE INVENTION

This description is given without limitation, each characteristic of an embodiment can be combined with any other characteristic of any other embodiment in an advantageous manner.

We note now that the figures are not to scale.

The present invention provides a method and a device having as a general principle the cooling by successive heat exchanges between natural gas or biogas with refrigerating bodies or mixtures. In this way, the temperature of the biogas or natural gas is gradually lowered until the liquefaction of said biogas or natural gas.

Preferably, this cooling in stages includes a pre-cooling by heat exchange between natural gas or biogas and a pure cooled refrigerant. This pre-cooling stage corresponds to the third heat exchange body 150 as described with reference to FIGS. 1, 4 and 5 and to the third heat exchange step 350 as described with regard to FIG. 3. This precooling can be carried out externally to the process or to the device which is the subject of the present invention, the precooled gas then being supplied to the first heat exchange step 330 or to the first heat exchange body 130.

This stepwise cooling includes, as the main cooling, a step of heat exchange between natural gas or biogas and cooled carbon dioxide. This cooling is preferably carried out after the pre-cooling step mentioned above.

This cooling in stages includes, as secondary cooling, called "liquefaction", a stage of heat exchange between natural gas or biogas and a cooled refrigerant. This cooling is carried out after the main cooling step mentioned above.

During this liquefaction step, the temperature of the gas is again lowered so that the gas is substantially liquefied.

Alternatively, the cold fluid used in the liquefaction stage passes, before being injected into the heat exchange body of this stage, the heat exchange body used in the main cooling stage and / or the pre-cooling step.

In alternative embodiments, the cooled carbon dioxide is cooled by heat exchange with the expanded coolant from the precooling step.

Thus, as we understand, the gas entering the process is gradually liquefied by the heat exchange between:

- gas and a pure coolant if the process includes a precooling step,

- gas, a cooling mixture and carbon dioxide, and

- the gas and the refrigerant mixture.

The present description discloses the object of the present invention, with reference to FIGS. 1, 3, 4 and 5, by first presenting the main cooling stage, then the pre-cooling stage and finally the stage liquefaction, these last two steps being optional.

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 liquefying a natural gas or biogas, comprises:

a first compressor 120 of vaporized carbon dioxide,

a first heat exchanger 125 for cooling the compressed carbon dioxide,

- a first heat exchange body 130 between:

the gas and the cooled carbon dioxide, the cooled carbon dioxide being supplied to a means 135 for expansion of the carbon dioxide,

the expanded gas and carbon dioxide, at the outlet of the means for expanding the carbon dioxide, the vaporized carbon dioxide being supplied to the first compressor, and

- expanded carbon dioxide and cooled carbon dioxide,

the means 135 for expanding the cooled carbon dioxide in the first exchange body, the expanded carbon dioxide being supplied to the first exchange body,

- a second compressor 105 of a refrigerant,

a second heat exchanger 110 for cooling the compressed refrigerant,

- a second body 160 for heat exchange between:

the gas leaving the first exchange body 130 and the cooled refrigerant, the cooled refrigerant being supplied to a means 115 for expansion of the refrigerant,

the gas leaving the first exchange body 130 and the expanded refrigerant, at the outlet of the expansion means of the refrigerant, the vaporized refrigerant being supplied to the second compressor and

- the expanded refrigerant and the cooled refrigerant,

- The means 115 for expansion of the cooled refrigerant in the second exchange body, the expanded refrigerant being supplied to the second exchange body.

The first compressor 120 is, for example, a dry piston compressor, a centrifugal compressor or an alternative compressor. This first compressor 120 makes it possible to raise the pressure of carbon dioxide. The carbon dioxide outlet pressure is set as a function of the saturated carbon dioxide pressure and the pressure drops in the carbon dioxide circuit in order to allow the liquid carbon dioxide to evaporate at a temperature between 35 ° C and -45 ° C. The evaporation temperature is chosen according to the approach of the heat exchanger; that is to say the minimum temperature difference, data communicated by the manufacturer. At the inlet of the first compressor 120, the carbon dioxide has a pressure of between 5 and 10 bar, preferably between 8 and 9 bar.

During this compression, the carbon dioxide undergoes significant heating and has a pressure greater than 20 bar, for example 36 bar. This flow of carbon dioxide is directed to the first heat exchanger 125 to be cooled there. This first heat exchanger 125 is, for example, a tubular exchanger using air or water as cold fluid. At the outlet of this first exchanger 125, the carbon dioxide is cooled to a temperature of approximately between preferably 7 ° C and 30 ° C, for example 24 ° C.

The carbon dioxide leaving this first exchanger 125 is then directed to the first exchange body 130.

This first exchange body 130 has two ends:

- one, called "hot", corresponds to the part of the first body 130 near the gas inlet in this first exchange body 130 and

- the other, called "cold", corresponds to the part of the first body 130 near the outlet of the cooled gas from this first exchange body 130.

Preferably, the cooled carbon dioxide leaving the first exchanger 125 is injected into the first exchange body 130 at the hot end of the first exchange body 130. The carbon dioxide is liquefied and sub-cooled during the heat exchange, with the expanded carbon dioxide and / or the cooling mixture, produced in the first exchange body 130.

The sub-cooled and liquefied carbon dioxide, which exhibits at the outlet of the first exchange body 130 a temperature of between -10 ° C. and 5 ° C., for example, is expanded in the means 135 for relaxing the carbon dioxide. The expansion means 135 is, for example, a Joule-Thomson valve performing isenthalpic expansion of the carbon dioxide. The cooled carbon dioxide is expanded to a pressure between 7 and 10 bar, for example, 9 bar. In variants, the expansion means 135 is an expansion turbine. Such an expansion turbine makes it possible to recover the expansion energy to drive the compression means of the device 100 and thus improve the energy efficiency of the process. The expanded carbon dioxide is then supplied to the first exchange body 130 so as to participate in the cooling of the gas and of the carbon dioxide cooled by the first heat exchanger 125.

The carbon dioxide vaporized during the heat exchange produced in the first exchange body 130 is supplied to the first compressor 120 so as to form a cycle. The first exchange body 130 is of type PFHE (for “Plate-fin heat exchanger”, translated by plate heat exchanger) or BAHX (for “Brazed aluminum heat exchanger”, translated by brazed aluminum heat exchanger) by example.

Thus, several heat exchanges take place within the first exchange body 130:

a first exchange between the expanded carbon dioxide and the cooled carbon dioxide to cool the expanded carbon dioxide, the cooled carbon dioxide being supplied to a means 135 for relaxing the carbon dioxide and

a second exchange between the gas and the expanded carbon dioxide to cool the gas, the vaporized carbon dioxide being supplied to the first compressor 120.

The first exchange body 130 is configured so that at the outlet, the gas has a temperature between -30 ° C and -40 ° C. At the inlet, the gas has a temperature between 0 and -10 ° C with preferably a temperature between -8 ° C and -10 ° C.

The refrigerant used during the liquefaction step, corresponding to the second heat exchange step 360 of FIG. 3, comprises, for example, nitrogen, methane, ethane, ethylene, propane, iso-butane, iso-pentane, normal butane and / or npentane. For example, the refrigerant consists of 99% methane. The refrigerant is preferably a pure body, but can also be a mixture. In particular, the refrigerant may be BOG ("Boil-off gas" for evaporative gas). This BOG can come from a tank on board a ship for example.

The second compressor 105 is, for example, a centrifugal or reciprocating compressor. This second compressor 105 allows, for example, to raise the pressure of the refrigerant to a pressure greater than 40 bar, preferably between 60 and 80 bar. At the inlet of the second compressor 105, the refrigerant has, for example, a pressure of between 2 barg and 4 barg preferably.

Preferably, this second compressor 105 compresses the refrigerant fluid in two successive compression stages. In variants, the compressed refrigerant is cooled by a heat exchanger (not shown) before being compressed in the second compression step. This heat exchanger (not shown) is, for example, a tubular exchanger using air or water as cold fluid. The heat exchanger produced between the two compression stages aims to ensure that the refrigerant does not exceed the temperature of 200 ° C.

The second heat exchanger 110 is, for example, a tubular exchanger using air or water as cold fluid. This second heat exchanger 110 aims to cool the compressed refrigerant to a temperature, preferably between 10 ° C and 25 ° C.

This second exchange body 160 has two ends:

- one, called "hot", corresponds to the part of the second body 160 near the gas inlet in this second exchange body 160 and

- the other, called "cold", corresponds to the part of the second body 160 near the outlet of cooled gas from this second exchange body 160.

Preferably, the cooled refrigerant leaving the second heat exchanger 110 is injected into the second exchange body 160 at the hot end of the second exchange body 160. The refrigerant is liquefied and sub-cooled during the heat exchange, with the expanded refrigerant.

The sub-cooled and liquefied refrigerant is expanded in the means 115 for expansion of the refrigerant. The expansion means 115 is, for example, a Joule-Thomson valve providing isenthalpic expansion of the refrigerant. The cooled refrigerant is expanded to a pressure, for example, between 2 barg and 4 barg. In variants, the expansion means 115 is an expansion turbine. Such an expansion turbine makes it possible to recover the expansion energy to drive the compression means of the device 100 and thus improve the energy efficiency of the process.

The expanded refrigerant is then supplied to the second exchange body 160 so as to participate in the cooling of the gas.

The refrigerant vaporized during the heat exchange produced in the second exchange body 160 is supplied to the second compressor 105 so as to form a cycle. The second exchange body 160 is of type PFHE (for “Plate-fin heat exchanger”, translated by plate heat exchanger) or BAHX (for “Brazed aluminum heat exchanger”, translated by brazed aluminum heat exchanger) by example.

Thus, several heat exchanges take place within the second exchange body 160:

a first exchange between the expanded refrigerant and the cooled refrigerant to cool the expanded carbon dioxide, the cooled refrigerant being supplied to a means 115 for expansion of the refrigerant and

a second exchange between the gas and the expanded coolant to cool the gas, the vaporized coolant being supplied to the second compressor 105.

The second exchange body 160 is configured so that at the outlet, the gas has a temperature below -140 ° C. At the inlet, the gas preferably has a temperature between -30 ° C and -40 ° C.

In embodiments, such as that shown in FIG. 4, the coolant leaving the second heat exchanger 110 is supplied to the first exchange body 130, the coolant being cooled by heat exchange with carbon dioxide in the first exchange body 130, the refrigerant leaving the first exchange body 130 being supplied to the second exchange body 160.

Preferably, the inlet for refrigerant fluid in this first exchange body 130 is positioned in the hot end and the outlet for this coolant is positioned in the cold end.

The refrigerant passing through the first exchange body 130 participates in the cooling of the gas and of the carbon dioxide cooled by the first heat exchanger 125.

The refrigerant cooled during the heat exchange produced in the first exchange body 130 is supplied to the second heat exchange body 160 so as to form a cycle.

In embodiments, such as those shown with reference to FIGS. 1, 4 and 5, the device, 100, 400 and / or 500, comprises:

- a third compressor 140 of a pure vaporized refrigerant,

a third heat exchanger 145 for cooling the compressed refrigerant compound,

- a third body 150 for heat exchange between:

the expanded coolant and the coolant to cool the coolant, the coolant being supplied to means 155 for expanding the coolant,

the gas and the expanded refrigerant to cool the gas, the vaporized refrigerant being supplied to the third compressor and the cooled gas being supplied to the first heat exchange body 130 and

the means 155 for expanding the cooled refrigerant in the third exchange body, the expanded refrigerant being supplied to the third exchange body.

The pure refrigerant is, for example, ammonia or propane.

The third compressor 140 is, for example, a centrifugal or reciprocating compressor. This compressor 140 allows, for example, to raise the pressure of the refrigerant to a pressure greater than 8 bar. At the inlet, the refrigerant compound preferably has a pressure greater than 2 bar.

The third heat exchanger 145 is, for example, a tubular exchanger using air or water as cold fluid, or glycol water for example. This third heat exchanger 145 aims to cool the compressed refrigerant mixture to a temperature of, for example, between 5 ° C and 20 ° C, for example 19 ° C.

The refrigerant leaving this third exchanger 145 is then directed to the third exchange body 150.

This third exchange body 150 has two ends:

- one, called "hot", corresponds to the part of the third body 150 near the gas inlet in this third exchange body 150 and

- the other, called "cold", corresponds to the part of the third body 150 near the outlet of cooled gas from this third exchange body 150.

Preferably, the cooled refrigerant compound leaving the third exchanger 145 is injected into the third exchange body 150 at the hot end of the third exchange body 150. The refrigerant is liquefied and sub-cooled during the heat exchange, with the expanded refrigerant made in the third exchange body 150.

Preferably, the entry for refrigerant compound in this third body

150 of exchange is positioned in the cold end and the outlet for this coolant is positioned in the hot end.

The expanded refrigerant mixture passing through the third exchange body 150 participates in the cooling of the gas and of the refrigerant compound cooled by the third heat exchanger 145.

The refrigerant compound vaporized during the heat exchange produced in the third exchange body 150 is supplied to the third compressor 140 so as to form a cycle.

The sub-cooled and liquefied refrigerant compound is expanded in the means 155 for expansion of the refrigerant compound. The expansion means 155 is, for example, a Joule-Thomson valve carrying out an isenthalpic expansion of the refrigerant compound. The cooled refrigerant is expanded to a pressure, preferably between 2 and 5 bar, and preferably around 3 bar. It is also possible that the refrigerant is expanded to a pressure below 2 bar, but there is then a risk that the suction pressure of the compressor 140 will no longer be sufficient. In variants, the expansion means 155 is an expansion turbine. Such an expansion turbine makes it possible to recover the expansion energy to drive the compression means of the device 100 and thus improve the energy efficiency of the process.

The expanded compound is then supplied to the third exchange body 150 so as to participate in the cooling of the gas and of the compound cooled by the third heat exchanger 145. The third exchange body 150 is of the PFHE or BAHX type for example.

The third exchange body 150 is configured so that at the outlet, the gas preferably has a temperature between 0 ° C and -10 ° C.

In embodiments, such as that produced opposite FIG. 5, the coolant leaving the second heat exchanger 110 is supplied to the third exchange body 150, the coolant being cooled by heat exchange with the coolant in the third exchange body 150, the refrigerant leaving the third exchange body 150 being supplied to the first exchange body 130.

In embodiments, such as that produced with reference to FIG. 5, the device 500 comprises a fourth body 505 for heat exchange between the refrigerant compound expanded at the outlet of the expansion means 155 and the carbon dioxide cooled at the outlet of the carbon dioxide cooling heat exchanger 125.

The fourth exchange body 505 is, for example, a plate exchanger.

In FIG. 2, we observe an embodiment of a boat 200 comprising a device 100, 400 or 500 as described with reference to FIGS. 1, 4 and

5.

FIG. 3 shows an embodiment of the method 300 which is the subject of the present invention. This process 300 for liquefying a natural gas or biogas, which comprises:

a first compression step 320 of vaporized carbon dioxide,

- a first heat exchange step 325 to cool the compressed carbon dioxide,

- a first stage of heat exchange 330 between:

the gas and the cooled carbon dioxide 330a, the cooled carbon dioxide being supplied in a step 335 of expansion of the carbon dioxide,

the gas and the expanded carbon dioxide 330b, at the outlet of step 335 of expansion of the carbon dioxide, the vaporized carbon dioxide being supplied in the first compression step 320 and

- expanded carbon dioxide and cooled carbon dioxide 330c,

the step 335 of expansion of the carbon dioxide cooled during the first heat exchange step 330, the expanded carbon dioxide being supplied to the first heat exchange step 330,

- a second compression step 305 of a refrigerant,

- a second stage of heat exchange 310 for cooling the compressed refrigerant,

- a second stage 360 of heat exchange between:

- the gas leaving the first exchange step 330 and the cooled refrigerant 360a, the cooled refrigerant being supplied to a step 315 of expansion of the refrigerant,

the gas leaving the first exchange step 330 and the expanded coolant 360b, at the outlet of the expansion step of the coolant, the vaporized coolant being supplied to the second compressor and

- the expanded refrigerant and the cooled refrigerant 360c,

- Step 315 of expansion of the coolant cooled during the second heat exchange step 360, the expanded coolant being supplied in the second heat exchange step.

In embodiments, such as that shown in FIG. 3, the refrigerant fluid leaving the second heat exchange step 310 is supplied to the first heat exchange step 330, the refrigerant fluid being cooled by heat exchange with the carbon dioxide during the first heat exchange step 330, the refrigerant leaving the first exchange step 330 being supplied to the second exchange step 360.

In embodiments, such as that shown in FIG. 3, the method 300 which is the subject of the present invention comprises:

- a third compression step 340 of a pure vaporized refrigerant,

- a third 345 heat exchange step for cooling the compressed refrigerant,

- a third stage 350 of heat exchange between:

the expanded coolant and the coolant to cool the coolant 350a, the coolant being supplied in a step 355 of expansion of the coolant,

the gas and the expanded refrigerant to cool the gas 350b, the vaporized refrigerant being supplied in the third compression step and the cooled gas being supplied in the first heat exchange step 330 and

- Step 355 of expansion of the coolant cooled during the third exchange step, the expanded coolant being supplied in the third exchange step.

In embodiments, such as that shown in FIG. 3, the refrigerant fluid leaving the second heat exchange step 310 is supplied to the third heat exchange step 350, the coolant being cooled by heat exchange with the refrigerant compound 350c during the third heat exchange stage 350, the refrigerant leaving the third exchange stage 350 being supplied to the first exchange stage 330.

In embodiments, such as that shown in FIG. 3, the method 300 which is the subject of the present invention comprises a fourth step 365 5 of heat exchange between the expanded refrigerant compound at the outlet of the expansion step 355 and the dioxide of carbon cooled at the outlet of the heat exchange step 325 for cooling carbon dioxide.

The method 300 is implemented, for example, by the device 500 as described with reference to FIG. 5.

Claims (12)

1. Device (100, 400, 500) for liquefying a natural gas or a biogas, characterized in that it comprises: - a first vaporized carbon dioxide compressor (120), - a first heat exchanger (125) for cooling the compressed carbon dioxide, - a first body (130) for heat exchange between: - the gas and the cooled carbon dioxide, the cooled carbon dioxide being supplied to a means (135) for expansion of the carbon dioxide, the expanded gas and carbon dioxide, at the outlet of the means for expanding the carbon dioxide, the vaporized carbon dioxide being supplied to the first compressor, and - expanded carbon dioxide and cooled carbon dioxide, the means (135) for expanding the cooled carbon dioxide in the first exchange body, the expanded carbon dioxide being supplied to the first exchange body, - a second compressor (105) of a refrigerant, - a second heat exchanger (110) for cooling the compressed refrigerant, - a second body (160) for heat exchange between: - the gas leaving the first exchange body (130) and the cooled refrigerant, the cooled refrigerant being supplied to a means (115) for expansion of the refrigerant, - The gas leaving the first exchange body (130) and the expanded refrigerant, at the outlet of the expansion means of the refrigerant, the vaporized refrigerant being supplied to the second compressor and - the expanded refrigerant and the cooled refrigerant, - The means (115) for expansion of the cooled refrigerant in the second exchange body, the expanded refrigerant being supplied to the second exchange body. 2. Device (400) according to claim 1, in which the coolant leaving the second heat exchanger (110) is supplied to the first exchange body (130), the coolant being cooled by heat exchange with the dioxide of carbon in the first exchange body (130), the refrigerant leaving the first exchange body (130) being supplied to the second exchange body (160). 3. Device (100, 400, 500) according to one of claims 1 or 2, which comprises: - a third compressor (140) of a pure vaporized coolant, - a third heat exchanger (145) for cooling the compressed refrigerant, - a third body (150) for heat exchange between: the expanded coolant and the coolant to cool the coolant, the coolant being supplied to means (155) for expanding the coolant, - the gas and the refrigerant expanded to cool the gas, the vaporized refrigerant being supplied to the third compressor and the cooled gas being supplied to the first heat exchange body (130) and - The means (155) for expansion of the cooled refrigerant in the third exchange body, the expanded refrigerant being supplied to the third exchange body. 4. Device (500) according to claim 3, in which the coolant leaving the second heat exchanger (110) is supplied to the third exchange body (150), the coolant being cooled by heat exchange with the coolant. in the third exchange body (150), the refrigerant leaving the third exchange body (150) being supplied to the first exchange body (130). 5. Device (500) according to one of claims 3 or 4, which comprises a fourth body (505) for heat exchange between the expanded refrigerant at the outlet of the expansion means (155) and the carbon dioxide cooled in outlet of the carbon dioxide cooling heat exchanger (125). 6. Device (500) according to one of claims 3 to 5, wherein the pure refrigerant is ammonia or propane. 7. Device (100, 400, 500) according to one of claims 1 to 6, in which the refrigerant mixture comprises nitrogen and / or methane. 8. Method (300) for liquefying a natural gas or biogas, characterized in that it comprises: - a first compression step (320) of vaporized carbon dioxide, - a first heat exchange step (325) to cool the compressed carbon dioxide, - a first heat exchange step (330) between: - the gas and the cooled carbon dioxide (330a), the cooled carbon dioxide being supplied in a step (335) of expansion of the carbon dioxide, - the expanded gas and carbon dioxide (330b), at the outlet of the step (335) for relaxing the carbon dioxide, the vaporized carbon dioxide being supplied in the first compression step (320) and - expanded carbon dioxide and cooled carbon dioxide (330c), the step (335) of relaxing the carbon dioxide cooled during the first heat exchange step (330), the expanded carbon dioxide being supplied in the first heat exchange step (330), - a second compression step (305) of a refrigerant, - a second heat exchange step (310) for cooling the compressed refrigerant, - a second stage (360) of heat exchange between: - the gas leaving the first exchange step (330) and the cooled refrigerant (360a), the cooled refrigerant being supplied in a step (315) of expansion of the refrigerant, the gas at the outlet of the first exchange step (330) and the expanded refrigerant (360b), at the outlet of the expansion step of the refrigerant, the vaporized refrigerant being supplied to the second compressor and - the expanded refrigerant and the cooled refrigerant (360c), - The step (315) of expansion of the coolant cooled during the second heat exchange step (360), the expanded coolant being supplied in the second heat exchange step. 9. The method (300) according to claim 8, in which the coolant leaving the second heat exchange step (310) is supplied to the first heat step (330), the coolant being cooled by exchange of heat with carbon dioxide during the first heat exchange step (330), the refrigerant leaving the first exchange step (330) being supplied in the second exchange step (360). 10. Method (300) according to one of claims 8 or 9, which comprises: - a third compression step (340) of a pure vaporized cooling compound, - a third heat exchange step (345) for cooling the compressed refrigerant, - a third stage (350) of heat exchange between: - the expanded refrigerant and the cooled refrigerant to cool the refrigerant (350a), the cooled refrigerant being supplied in a step (355) of expansion of the refrigerant, - the gas and the expanded refrigerant to cool the gas (350b), the vaporized refrigerant being supplied in the third compression step and the cooled gas being supplied in the first heat exchange step (330) and - Step (355) of expansion of the coolant cooled during the third exchange step, the expanded coolant being supplied in the third exchange step. 11. The method (300) as claimed in claim 10, in which the coolant leaving the second heat exchange step (310) is supplied to the third heat step (350), the coolant being cooled by exchange of heat with the refrigerant compound (350c) during the third heat exchange stage (350), the refrigerant leaving the third exchange stage (350) being supplied in the first exchange stage (330) . 12. Method (300) according to one of claims 10 or 11, which comprises a fourth step (365) of heat exchange between the expanded refrigerant at the outlet of the expansion step (355) and carbon dioxide cooled at the outlet of the heat exchange step (325) for cooling the carbon dioxide.