WO2019008269A1

WO2019008269A1 - Device and method for liquefying natural gas or biogas

Info

Publication number: WO2019008269A1
Application number: PCT/FR2018/051654
Authority: WO
Inventors: Hicham GUEDACHA
Original assignee: Engie
Priority date: 2017-07-05
Filing date: 2018-07-03
Publication date: 2019-01-10
Also published as: EP3649417A1; KR20200023359A; BR112020000215A2; FR3068771B1; FR3068771A1

Abstract

The invention relates to a method (300) for liquefying a natural gas or a biogas, said method comprising: a first step (305) of compressing a vaporised refrigerant mixture; a first heat exchange step (310) for cooling the compressed refrigerant mixture; a step (315) of expanding the cooled refrigerant mixture; a second step (320) of compressing vaporised carbon dioxide; a second heat exchange step (325) for cooling the compressed carbon dioxide; a first step (330) of heat exchange between: the gas and the expanded refrigerant mixture (330a) in order to cool the gas, the vaporised refrigerant mixture being supplied in the first compression step, the expanded refrigerant mixture and the cooled carbon dioxide (330b) in order to cool the carbon dioxide, the cooled carbon dioxide being supplied in a step of expansion of the carbon dioxide, and the gas and the expanded carbon dioxide (330c) in order to cool the gas, the vaporised carbon dioxide being supplied in the second compression step; and the step (335) of expansion of the carbon dioxide cooled in the first heat exchange step, the expanded carbon dioxide being supplied in the first heat exchange step.

Description

DEVICE AND METHOD FOR LIQUEFACTION OF A NATURAL GAS OR A

BIOGAS

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 the evaporation gas.

STATE OF THE ART

The liquefaction of the gas allows the transport of natural gas at a lower volume compared to the transport of the 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 high transport costs (marine liquefaction and reception infrastructures). Thus, on the one hand, the trend of 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 sizing and the construction of liquefaction processes to be as effective as possible in order to minimize operating costs thereafter.

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

Indeed, the valorization of small sources of gas, fatal gases and biogas are new opportunities promoted notably 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, however, too small to justify the use of technologies for large-scale production (the transposition of traditional technologies is not relevant because it is too complex and does not justify the economic viability of these new projects), hence the need to propose new technologies that can address the three main issues related to small-scale liquefaction :

- the reduction of 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 the loss of product: the volumes of gas to be valorized 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 able to be a pure substance or a refrigerant mixture in order to improve the efficiency,

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

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

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

Brayton's processes have the drawbacks of medium to low energy performance, capital investment and operating costs, and the need for bulky equipment.

Open cycle processes have the drawbacks of having low energy performance and high energy supply cost. OBJECT OF THE INVENTION

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

To remedy all or part of these disadvantages, the present invention provides a method and a device having as a general principle cooling by successive heat exchanges between the natural gas or the biogas with bodies or refrigerant 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 pre-cooling by heat exchange between the natural gas or the biogas and a cooled pure refrigerant.

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

Preferably, the method and the device of the present invention comprise an additional cooling step, downstream of the cooling step, between the natural gas or the biogas and the cooled refrigerant mixture. The cooled mixture reheated during the additional cooling step is supplied to the cooling step.

Each refrigerant compound or mixture and the carbon dioxide is cooled either downstream of the pre-cooling step or downstream of the cooling step.

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

a first compressor of a vaporized refrigerant mixture,

a first heat exchanger for cooling the compressed refrigerant mixture,

a means for relaxing the cooled refrigerant mixture,

a second vaporized carbon dioxide compressor,

a second heat exchanger for cooling the compressed carbon dioxide,

a first heat exchange body between:

the gas and the refrigerant mixture expanded to cool the gas, the vaporized refrigerant mixture being supplied to the first compressor, the expanded refrigerant mixture and the cooled carbon dioxide for cooling the carbon dioxide, the cooled carbon dioxide being supplied to a means of expansion of the carbon dioxide,

the expanded gas and carbon dioxide for cooling the gas, the vaporized carbon dioxide being supplied to the second compressor and

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

Thanks to these arrangements, the device that 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,

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

- minimizes refrigerant flow rates.

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

to reduce the flow rate of the refrigerant cycle and therefore the size of the compressor required in comparison with a process that does not use 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 compounds and heavier hydrocarbons potentially crystallizable for the liquefaction of the gas.

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

a third compressor of a vaporized pure refrigerant compound,

a third heat exchanger for cooling the compressed refrigerant compound,

a second heat exchange body between:

the expanded refrigerant compound and the refrigerant compound cooled to cool the refrigerant compound, the cooled refrigerant compound being supplied to an expansion means of the refrigerant compound, the gas and the refrigerant compound expanded to cool the gas, the vaporized refrigerant being supplied to the third compressor and the gas being supplied to the first heat exchange body and the expansion means of the chilled refrigerant in the second heat sink exchange, the expanded refrigerant being supplied to the second exchange body.

These embodiments make it possible to pre-cool the gas before this gas passes through the first heat exchange body.

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

These embodiments make it possible to minimize the use of explosive compounds.

In embodiments, the device of the present invention comprises, downstream of the first exchange body on the path traveled by the gas, a third heat exchange body between the gas and the refrigerant mixture expanded to cool the gas. gas, the refrigerant mixture at the outlet being supplied to the first exchange body.

These embodiments allow the gas to be further cooled after this gas passes through the first heat exchange body.

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

These embodiments make it possible to limit the use of explosive compounds.

In embodiments, the device that is the subject of the present invention comprises a means for collecting evaporation gas in a liquefied gas tank, the collected evaporation gas being used in the cooling mixture.

These embodiments make it possible to exploit the evaporation gas as a refrigerant (without the need for fractionation or separation), this evaporation gas being usually used to generate the energy necessary to drive the compressors.

In embodiments, at least one hot fluid and at least one cold fluid in an exchange body flow countercurrently to each other.

These embodiments make it possible to maximize the heat transfer between the hot fluid and the cold fluid. According to a second aspect, the present invention relates to a process for liquefying a natural gas or a biogas, which comprises:

a first step of compressing a vaporized refrigerant mixture,

a first heat exchange stage for cooling the compressed refrigerant mixture,

a step of relaxing the cooled refrigerant mixture,

a second step of compression of vaporized carbon dioxide,

a second heat exchange stage for cooling the compressed carbon dioxide,

a first step of heat exchange between:

the gas and the refrigerated mixture expanded to cool the gas, the vaporized refrigerant mixture being supplied to the first compression stage,

the expanded refrigerant mixture and the cooled carbon dioxide for cooling the carbon dioxide, the cooled carbon dioxide being supplied to a carbon dioxide expansion stage,

- gas and carbon dioxide expanded to cool the gas, the vaporized carbon dioxide being supplied to the second stage of compression and

the step of expanding the cooled carbon dioxide in the first heat exchange stage, the expanded carbon dioxide being supplied to the first heat exchange stage.

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

a third step of compression of a vaporized pure refrigerant compound,

a third heat exchange stage for cooling the compressed refrigerant compound,

a second heat exchange step between:

the expanded refrigerant compound and the refrigerant compound, cooled to cool the refrigerant compound, the refrigerant compound cooled during this step being supplied to a step of expansion of the refrigerant compound,

the gas and the refrigerant compound expanded to cool the gas, the vaporized refrigerant compound being supplied to the third step of compression and the gas being supplied at the first stage of heat exchange and

the step of expanding the cooled refrigerant compound in the second heat exchange stage, the expanded refrigerant being supplied to the second heat exchange stage.

In embodiments, the method that is the subject of the present invention comprises, downstream of the first step of heat exchange on the path traversed by the gas, a third step of heat exchange between the gas and the relaxed refrigerant mixture. for cooling the gas, the output refrigerant mixture being supplied to the first heat exchange stage.

Since the aims, advantages and particular characteristics of the method which are the subject of the present invention being similar to those of the device which is the subject of the present invention, they are not recalled here. BRIEF DESCRIPTION OF THE FIGURES

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

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

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

- Figure 3 shows schematically and in the form of a logic diagram, a particular sequence of steps of the method object of the present invention.

DESCRIPTION OF EXAMPLES OF CARRYING OUT THE INVENTION

This description is given in a nonlimiting manner, each feature of an embodiment being able to be combined with any other feature of any other embodiment in an advantageous manner.

It is already noted that the figures are not to scale.

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

Preferably, this step cooling includes pre-cooling by heat exchange between the natural gas or biogas and a cooled pure refrigerant. This pre-cooling stage corresponds to the second heat exchange body 150 as described with reference to FIG. 1 and the second heat exchange stage 350 as described with reference to FIG. 3. This pre-cooling can be produced externally to the method or device of the present invention, the pre-cooled gas then being supplied to the first heat exchange step 330 or to the first heat exchange body 130.

This step cooling includes, as main cooling, a heat exchange step between the natural gas or the biogas, a refrigerant mixture and cooled carbon dioxide. This cooling is preferably carried out after the pre-cooling step mentioned above. However, it is possible that the gas leaving this stage is not yet completely liquefied, and the stepwise cooling then preferably includes an additional cooling stage, or liquefaction stage of the gas, downstream of the main cooling stage.

During this liquefaction stage, the temperature of the gas is lowered again so that the gas is substantially liquefied. This liquefaction step can be carried out downstream of the method that is the subject of the present invention by a third-party device.

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

the gas and a pure refrigerant compound if the process includes a pre-cooling step,

- gas, a refrigerant mixture and carbon dioxide and

the gas and the refrigerant mixture if the process includes a liquefaction step.

The present disclosure discloses the object of the present invention, with reference to FIGS. 1 and 3, presenting initially the main cooling stage, then the pre-cooling stage and finally the liquefaction stage. 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 of liquefaction of a natural gas or a biogas comprises:

a first compressor 105 of a vaporized refrigerant mixture,

a first heat exchanger 1 for cooling the compressed refrigerant mixture,

a means 1 for relaxing the cooled refrigerant mixture,

a second compressor 120 of vaporized carbon dioxide,

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

a first heat exchange body 130 between:

the gas and the refrigerant mixture expanded to cool the gas, the vaporized refrigerant mixture being supplied to the first compressor,

the expanded refrigerant mixture and the cooled carbon dioxide for cooling the carbon dioxide, the cooled carbon dioxide being supplied to a means for the expansion of the carbon dioxide,

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

The cooling mixture comprises, for example, nitrogen, methane, ethane, ethylene, propane, iso-butane, iso-pentane, normal butane and / or npentane.

The first compressor 105 is, for example, a centrifugal or reciprocating compressor. This compressor 105 allows, for example, to increase the pressure of the refrigerant mixture at a pressure preferably between 30 and 80 bar, and about 40 bar for example.

Preferably, this first compressor 105 compresses the refrigerant mixture in two successive compression stages. In variants, the compressed refrigerant mixture 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 as cold fluid air or water. The heat exchanger realized between the two compression steps is that the refrigerant mixture does not exceed the temperature of 200 ° C.

The first heat exchanger 1 is, for example, a tubular exchanger using as cold fluid air or water. This first heat exchanger 1 10 aims to cool the compressed refrigerant mixture at a temperature preferably between 10 and 25 ° C.

The expansion means 1 is, for example, a Joule-Thomson valve performing isenthalpic expansion of the refrigerant mixture. The cooled refrigerant mixture is expanded to a pressure of between 2 barg and 4 barg, for example preferably 4 bar. In variants, the expansion means 1 15 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 cooling mixture thus expanded is supplied to the first heat exchange body 130 for cooling the gas passing through this first exchange body 130 and carbon dioxide also passing through this first body 130 exchange.

The second compressor 120 is, for example, a dry piston compressor, a centrifugal compressor or an alternating compressor. This second compressor 120 makes it possible to raise the pressure of the carbon dioxide. The carbon dioxide output pressure is set according to the saturating pressure of the carbon dioxide and the carbon dioxide system pressure drop 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 temperature of approach of the heat exchanger, data given by the manufacturer.

During this compression, the carbon dioxide undergoes a significant warming. This flow of carbon dioxide is directed to the second heat exchanger 125 to be cooled. This second heat exchanger 125 is, for example, a tubular exchanger using as cold fluid air or water. At the outlet of this second exchanger 125, the carbon dioxide is cooled to a temperature preferably between 7 ° C. and 30 ° C., for example 15 ° C.

Carbon dioxide leaving this second exchanger 125 is then directed to the first body 130 exchange.

This first body 130 of exchange has two ends: one, so-called "hot", corresponds to the part of the first body 130 near the gas inlet in this first body 130 exchange and

- The other, called "cold", corresponds to the portion of the first body 130 near the cooled gas outlet of the first body 130 exchange.

Preferably, the cooled carbon dioxide leaving the second 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 subcooled during the heat exchange, with the expanded carbon dioxide and / or the refrigerant mixture, produced in the first exchange body 130.

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

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

The vaporized refrigerant mixture during the heat exchange made in the first exchange body 130 is supplied to the first compressor 105 so as to form a cycle.

The carbon dioxide undercooled and liquefied is expanded in the means 135 for expansion of carbon dioxide. The means 135 of relaxation is, for example, a Joule-Thomson valve performing isenthalpic expansion of carbon dioxide. The cooled carbon dioxide is expanded at a pressure of, for example, 8 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 the carbon dioxide cooled by the second heat exchanger 125.

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

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

a first exchange between the gas and the expanded refrigerant mixture to cool the gas, the vaporized refrigerant mixture being supplied to the first compressor 105,

a second exchange between the expanded refrigerant mixture and the cooled carbon dioxide for cooling the carbon dioxide, the cooled carbon dioxide being supplied to a carbon dioxide expansion means 135 and

a third exchange between the gas and the expanded carbon dioxide for cooling the gas, the vaporized carbon dioxide being supplied to the second 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. As input, the gas has a temperature between 0 and -10 ° C with preferably a temperature between -8 ° C and -10 ° C.

In preferred embodiments, such as that represented in FIG. 1, the device 100 comprises:

a third compressor 140 of a vaporized pure refrigerant compound,

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

a second body 150 of heat exchange between:

the expanded refrigerant compound and the cooled refrigerant compound for cooling the refrigerant compound, the cooled refrigerant compound being supplied to a means 155 for expanding the refrigerant compound,

the gas and the refrigerant compound 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 expanding the cooled refrigerant in the second exchange body, the expanded refrigerant being supplied to the second exchange body.

The pure refrigerant compound 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 compound to a pressure greater than 20 bar, for example about 35 bar.

The third heat exchanger 145 is, for example, a tubular exchanger using as cold fluid air or water, or brine, for example. This third heat exchanger 145 aims to cool the compressed refrigerant mixture to a temperature of, for example, between 5 and 20 ° C, for example 15 ° C.

The refrigerant compound leaving this third exchanger 145 is then directed towards the second exchange body 150.

This first exchange body 150 has two ends:

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

- The other, called "cold", corresponds to the portion of the second body 150 near the cooled gas outlet of the second body 150 exchange.

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

Preferably, the refrigerant inlet in this second exchange body 150 is positioned in the cold end and the outlet for this refrigerant compound is positioned in the hot end.

The expanded refrigerant mixture passing through the second exchange body 150 contributes to 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 made in the second exchange body 150 is supplied to the third compressor 140 so as to form a cycle.

The cooled and liquefied refrigerant compound is expanded in the means 155 for expanding the refrigerant compound. The expansion means 155 is, for example, a Joule-Thomson valve providing isenthalpic expansion of the refrigerant compound. In variants, the expansion means 155 is an expansion turbine. Such an expansion turbine makes it possible to recover the relaxing energy to drive the compression means of the device 100 and thus improve the energy efficiency of the process. The cooled refrigerant compound is expanded to a pressure, preferably between 2.5 and 4 bar, and preferably about 3.5 bar. It is also possible that the refrigerant compound is expanded to a pressure below 2.5 bar, but there is then a risk that the suction pressure of the compressor 140 is no longer sufficient.

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

The second exchange body 150 is configured so that, at the outlet, the gas has a lower temperature of between 0 ° C. and -10 ° C., for example.

In preferred embodiments, such as that shown in FIG. 1, the device 100 comprises, downstream of the first exchange body on the path traversed by the gas, a third heat exchange body 160 between the gas and the gas. refrigerant mixture expanded to cool the gas, the output refrigerant mixture being supplied to the first body 130 exchange. The third exchange body 160 is of the PFHE or BAHX type, for example.

The third exchange body 160 is configured so that, at the outlet, the gas has a temperature below -155 ° C. preferentially.

In preferred embodiments, such as that shown in Figure 1, the device 100 comprises a means 165 for collecting evaporation gas in a tank 170 of liquefied gas, the evaporation gas collected being used in the refrigerant mixture.

The means 165 for collecting is, for example, an aspiration of evaporation gas located in an upper part of the tank 170. For example, an alternative compressor is used to transfer the BOG from the storage to the injection site. The refrigerant mixture used in the present device is then configured to preferentially present a composition close to a composition typical of a BOG of liquefied natural gas. The regulation of the temperature of the LNG produced is preferably regulated by acting on the flow of refrigerant mixture at first, and secondly on the flow of natural gas to be liquefied. Similarly, in the pre-cooling stage, the flow rate of pure refrigerant can be regulated so as to cool at a predetermined temperature the gas entering said pre-cooling stage.

In embodiments, such as that represented in FIG. 1, at least one hot fluid and at least one cold fluid in a body, 130, 150 and / or 160, exchange counter-current to one of the 'other.

FIG. 2 diagrammatically shows a boat comprising a device 100 as described with reference to FIG.

FIG. 3 diagrammatically shows a particular flow diagram of the process 300 which is the subject of the present invention. This method 300 of liquefaction of a natural gas or a biogas comprises:

a first step 305 for compressing a vaporized refrigerant mixture,

a first heat exchange stage 310 for cooling the compressed refrigerant mixture,

a step 315 for relaxing the cooled refrigerant mixture,

a second vaporized carbon dioxide compression step 320,

a second stage 325 of thermal exchange for cooling the compressed carbon dioxide,

a first step 330 of heat exchange between:

the gas and the expanded refrigerant mixture 330a for cooling the gas, the vaporized refrigerant mixture being supplied to the first compression stage,

the expanded refrigerant mixture and the cooled carbon dioxide 330b for cooling the carbon dioxide, the cooled carbon dioxide being supplied to a carbon dioxide expansion step, the expanded gas and carbon dioxide 330c for cooling the gas , the vaporized carbon dioxide being supplied to the second compression stage and

the step 335 for relaxing the carbon dioxide cooled in the first heat exchange stage, the expanded carbon dioxide being supplied to the first heat exchange stage.

In embodiments, such as that shown in FIG. 3, the method 300 comprises:

a third step 340 of compression of a vaporized pure refrigerant compound, a third heat exchange stage 345 for cooling the compressed refrigerant compound,

a second heat exchange step 350 between:

the expanded refrigerant compound and the refrigerant compound 350a, cooled to cool the refrigerant compound, the refrigerant compound cooled during this step being supplied to a step of expansion of the refrigerant compound,

the gas and the expanded refrigerant 350b for cooling the gas, the refrigerant compound being supplied to the third compression stage and the cooled gas being supplied to the first heat exchange stage and

step 355 of expanding the cooled refrigerant compound in the second heat exchange stage, the expanded refrigerant being supplied to the second heat exchange stage.

In embodiments, such as that represented in FIG. 3, the method 300 comprises, downstream of the first heat exchange step 330 on the path traversed by the gas, a third heat exchange step 360 between the gas and the expanded refrigerant mixture for cooling the gas, the output-cooled gas being supplied to the first heat exchange stage.

The method 300 is implemented, for example, by the device 100 as described with reference to FIG.

Claims

1. Device (100) for liquefying a natural gas or a biogas, characterized in that it comprises:

a first compressor (105) of a vaporized refrigerant mixture,

a first heat exchanger (1 10) for cooling the compressed refrigerant mixture,

means (1 15) for expanding the cooled refrigerant mixture,

a second compressor (120) of vaporized carbon dioxide,

a second (125) compressed carbon dioxide cooling heat exchanger,

a first body (130) for exchanging heat between:

the expanded refrigerant mixture and the cooled carbon dioxide for cooling the carbon dioxide, the cooled carbon dioxide being supplied to means (135) for the expansion of the 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.

2. Device (100) according to claim 1, which comprises:

a third compressor (140) of a vaporized pure refrigerant compound,

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

a second body (150) for exchanging heat between:

the expanded refrigerant compound and the cooled refrigerant compound for cooling the refrigerant compound, the cooled refrigerant compound being supplied to a means (155) for expanding the refrigerant compound, the gas and the refrigerant compound expanded to cool the gas, the refrigerant compound vaporized 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 refrigerant cooled in the second exchange body, the expanded refrigerant being supplied to the second exchange body.

3. Device (100) according to claim 2, wherein the pure refrigerant compound is ammonia or propane.

4. Device (100) according to one of claims 1 to 3, which comprises, downstream of the first exchange body on the path traveled by the gas, a third (160) heat exchange body between the gas and the refrigerant mixture expanded to cool the gas, the output refrigerant mixture being supplied to the first exchange body (130).

5. Device (100) according to one of claims 1 to 4, wherein the refrigerant mixture comprises nitrogen and / or methane.

6. Device (100) according to one of claims 1 to 5, which comprises means (165) for collecting evaporation gas in a tank (170) of liquefied gas, the evaporation gas collected being used in the refrigerant mixture.

7. Device (100) according to one of claims 1 to 6, wherein at least one hot fluid and at least one cold fluid in a heat exchange body flow countercurrently with each other.

8. Process (300) for liquefying a natural gas or a biogas, characterized in that it comprises:

a first step (305) of compression of a vaporized refrigerant mixture,

a first heat exchange step (310) for cooling the compressed refrigerant mixture,

a step (315) for relaxing the cooled refrigerant mixture,

a second vaporized carbon dioxide compression step (320),

a second heat exchange stage (325) for cooling the compressed carbon dioxide, a first step (330) of heat exchange between:

the gas and the expanded refrigerant mixture (330a) for cooling the gas, the vaporized refrigerant mixture being supplied to the first compression stage,

the expanded refrigerant mixture and the cooled carbon dioxide (330b) for cooling the carbon dioxide, the cooled carbon dioxide being supplied to a carbon dioxide expansion step,

the gas and the expanded carbon dioxide (330c) for cooling the gas, the vaporized carbon dioxide being supplied to the second compression stage and

the step (335) for relaxing the cooled carbon dioxide in the first heat exchange step, the expanded carbon dioxide being supplied to the first heat exchange step.

The process (300) of claim 8 which comprises:

a third step (340) for compressing a vaporized pure refrigerant compound,

a third cooling heat exchange step (345) for the compressed refrigerant compound,

a second heat exchange step (350) between:

the expanded refrigerant compound and the refrigerant compound (350a), cooled to cool the refrigerant compound, the refrigerant compound cooled during this step being supplied to a step of expanding the refrigerant compound,

the gas and the expanded refrigerant compound (350b) for cooling the gas, the refrigerant compound being supplied to the third compression stage and the cooled gas being supplied to the first heat exchange stage and

the step (355) of expanding the cooled refrigerant compound in the second heat exchange stage, the expanded refrigerant being supplied to the second heat exchange stage.

10. Method (300) according to one of claims 8 or 9, which comprises, downstream of the first step (330) of heat exchange on the path traveled by the gas, a third step (360) of exchange of heat between the gas and the refrigerant mixture expanded to cool the gas, the output coolant being provided first heat exchange step.