WO2005103583A1

WO2005103583A1 - Method for the liquefaction of a gas involving a thermo-acoustic cooling apparatus

Info

Publication number: WO2005103583A1
Application number: PCT/FR2005/000405
Authority: WO
Inventors: Béatrice Fischer
Original assignee: Institut Francais Du Petrole
Priority date: 2004-03-23
Filing date: 2005-02-21
Publication date: 2005-11-03
Also published as: AU2005236214A1; FR2868154A1; FR2868154B1; MY136422A; AU2005236214B2

Abstract

The gas circulating in the conduit (1) is cooled and liquefied under pressure in the heat exchanger (11). The gas emanating from the heat exchanger (11) via the conduit (2) is guided by the conduit (3) into the expansion device (13). The gas is expanded until it reaches a pressure which is close to atmospheric pressure. The fluid discharged via the conduit (4) makes up the liquefied gas, e.g. liquefied natural gas. The refrigeration cycle consists of a refrigerating fluid which circulates inside the compressor (20), condenser (21), heat exchanger (11) and expansion device (229). According to the invention, a thermo-acoustic refrigeration apparatus cools the fluid obtained at the output of the heat exchanger (11) via the conduit (3), and a thermo-acoustic refrigeration apparatus (23) cools the fluid obtained at the output of the exchanger (11) via the conduit (24).

Description

METHOD FOR LIQUEFACTION OF A GAS INTEGRATING A THERMOACOUSTIC COOLING APPARATUS

The present invention relates to the field of liquefaction of a gas, using thermo-acoustic cooling equipment. The purpose of the process according to the invention is to liquefy by cooling gases, for example neon, hydrogen, helium or natural gas. By natural gas is meant a gas, liquid or two-phase mixture comprising at least 50% methane, and possibly other hydrocarbons and nitrogen. Natural gas is generally produced in gaseous form, and at high pressure, for example between 1 MPa and 15 MPa. The liquefaction of natural gas consists in condensing the gas, then in sub-cooling it to a temperature low enough that it can remain liquid at atmospheric pressure. Then, the liquid natural gas is transported in LNG carriers.

Currently, international trade in liquid natural gas (LNG) is growing rapidly. However, the entire production chain of

LNG requires considerable investment and operating costs. Document FR 2 778 232 proposes a liquefaction process comprising two refrigerant mixtures circulating in two closed and independent circuits. Each of the circuits operates thanks to a compressor communicating with the refrigerant mixture the power necessary to cool natural gas. Each compressor is driven by a gas turbine which is chosen from the standard ranges offered on the market. However, the power of the gas turbines currently available is limited. So the LNG production capacity of a liquefaction unit is limited by the power of gas turbines. The present invention proposes to improve the process disclosed in document FR 2 778 232 in order to increase the liquefaction power while keeping the compressors standard.

The present invention proposes to combine a conventional liquefaction process with cooling operated by a thermo-acoustic refrigeration apparatus.

In general, the present invention relates to a process for liquefying a gas, the gas being available under a pressure P1. The gas undergoes the following steps: - the gas under pressure PI is condensed by heat exchange with a coolant so as to obtain a liquid under pressure PI, the coolant being vaporized during the heat exchange, and - the liquid under pressure P1 to a pressure P2, The refrigerant undergoes the following steps: - the vaporized refrigerant is compressed, - the compressed refrigerant is cooled, the cooled refrigerant is expanded, the expanded refrigerant condenses the gas under PI pressure by heat exchange, And, at least one of the following two steps is carried out: before expansion, the liquid under PI pressure is sub-cooled by a first thermo-acoustic cooling device, before expansion, we - cools the coolant cooled by a second thermo-acoustic cooling device. According to the invention, the gas can be a natural gas at a pressure between 1 MPa and 15 MPa and at a temperature between 20 ° C and 60 ° C. The first thermo-acoustic cooling device can lower the temperature of the cooled liquid by a value between 1 ° C to

20 ° C. The second thermo-acoustic cooling device can lower the temperature of the cooled refrigerant by between 1 ° C and 20 ° C. According to the invention, the thermo-acoustic cooling devices can comprise: a heat engine supplied with heat, which generates an acoustic wave, - a resonator in which the thermo-acoustic wave is established, - a refrigerator, arranged downstream of the resonator, using the energy of the acoustic wave to produce a cold spot at low temperature. According to the invention, the liquid under pressure PI can be sub-cooled by several thermo-acoustic cooling devices arranged in parallel. The cooled refrigerant can be sub-cooled by several thermo-acoustic cooling devices arranged in parallel.

Thermo-acoustic refrigeration equipment increases the production capacity of a conventional liquefaction process. In addition, the thermo-acoustic refrigeration equipment makes it possible to modify the production capacity without modifying the operation of the gas turbines supplying the energy to the refrigerant circuits. Other characteristics and advantages of the invention will be better understood and will become clear on reading the description given below with reference to the drawings among which: - Figures 1, 2 and 3 show diagrammatically the process according to the invention, - Figure 4 shows a liquefaction process according to the prior art, - Figures 5, 6 and 7 schematize particular embodiments of the invention, - Figure 8 shows the principle of a thermo-acoustic cooling apparatus .

FIG. 1 schematically represents a process for liquefying a gas by compression and expansion of a refrigeration fluid. The gas arriving through line 1 is under pressure, for example at a pressure between 1 MPa and 15 MPa. For example, the gas has been compressed by a compressor, or, in the case of natural gas, the gas is obtained under pressure at the outlet of the production well. The gas flowing in the pipe 1 is cooled and liquefied under pressure in the heat exchanger 11. The gas coming from the heat exchanger 11 through the pipe 2 is brought by the pipe 3 in the expansion device 13, for example a valve and / or an expansion turbine. The gas is expanded to a pressure close to atmospheric pressure. The fluid discharged through line 4 constitutes the liquefied gas, for example liquefied natural gas. The refrigeration cycle consists of a refrigerant circulating in the organs 20, 21, 11 and 22. This cycle is simplified and can be modified and supplemented without departing from the scope of the invention. Compressor 20, which can be driven by a gas turbine, provides the necessary cooling power. The refrigeration fluid is compressed in the compressor 20, cooled and partially or totally condensed in the heat exchanger 21, for example by heat exchange with water or with ambient air. Then, the refrigeration fluid is sub-cooled in the exchanger 11, then evacuated through the conduit 24. Advantageously, the refrigeration fluid obtained at the outlet of the exchanger 11 is liquid. Then, the refrigeration fluid is expanded in the expansion device 22 to be cooled, then is sent to the heat exchanger 11 to be heated and vaporized there, before being returned to the compressor 20. For example the refrigerant can be a mixture of nitrogen and hydrocarbons such as methane, ethane and propane. According to the invention, a thermo-acoustic refrigeration apparatus 12 cools the fluid obtained at the outlet of the exchanger 11 through the conduit 2. The refrigeration apparatus operates a reduction in the temperature of the fluid by a value between 1 ° C and 20 ° C, preferably between 1 ° C and 5 ° C. The thermo-acoustic refrigeration equipment is described more fully below, in relation to FIG. 8.

FIG. 2 represents a variant of the method according to the invention. The references in Figure 2 identical to those in Figure 1 denote the same elements. The process shown schematically in FIG. 2 is identical to the process shown schematically in FIG. 1, except that according to the process in FIG. 2, the thermo-acoustic refrigeration apparatus is not disposed on the duct 3. On the other hand, in FIG. 2, the refrigeration apparatus 23 is arranged on the duct 24. In FIG. 2, the thermo-acoustic refrigeration apparatus 23 cools the fluid obtained at the outlet of the exchanger 11 by the conduit 24. The refrigeration apparatus 23 operates a lowering of the temperature of the fluid by a value between 1 ° C and 20 ° C, preferably between 1 ° C and 5 ° C.

FIG. 3 represents a variant of the method according to the invention. The references in Figure 3 identical to those in Figure 1 denote the same elements. The process shown schematically in FIG. 3 is identical to the process shown schematically in FIG. 1, except that according to the process in FIG. 3, an additional thermo-acoustic refrigeration apparatus 23 is placed on the duct 24. In FIG. 3, the thermo-acoustic refrigeration apparatus 12 cools the fluid obtained at the outlet of the exchanger 11 through the conduit 2, and the thermo-acoustic refrigeration apparatus 23 cools the fluid obtained at the outlet of the exchanger 11 through the conduit 24 Apparatuses 11 and 23 lower the temperature by between 1 ° C and 20 ° C, preferably between 1 ° C and 5 ° C.

FIG. 4 represents a process for liquefying natural gas according to the prior art. This process is described in particular in document FR 2 778 232. According to the natural gas liquefaction process shown diagrammatically in FIG. 4, the natural gas arriving through line 101 is cooled by indirect heat exchange with two refrigerant mixtures, each refrigerant mixture circulating in a closed and independent circuit. Natural gas arrives via line 101, for example at a pressure between 1 MPa and 15 MPa, preferably between 4 MPa and 7 MPa and at a temperature between 20 ° C and 60 ° C. The gas circulating in the conduit 101, the first refrigerant mixture circulating in the conduit 135 and the second refrigerant mixture circulating in the conduit 123 enter the heat exchanger 111 to circulate there in parallel and co-current directions. Natural gas leaves the exchanger 111 through the conduit 102, for example at a temperature between - 35 ° C and - 70 ° C. The second refrigerant mixture leaves completely condensed from the exchanger 111 through the conduit 124, for example at a temperature between - 35 ° C and - 70 ° C. In the exchanger 111, three fractions of the first refrigerant mixture in the liquid phase are successively withdrawn. The fractions are expanded through the expansion valves 132, 133 and 134 at three different pressure levels, then vaporized in the exchanger 111 by heat exchange with natural gas, the second refrigerant mixture and part of the first refrigerant mixture. The three vaporized fractions are sent to different stages of the compressor 130. The vaporized fractions are compressed in the compressor 130, then condensed in the condenser 131 by heat exchange with an external cooling fluid, for example water or air. The first refrigerant mixture from the condenser 131 is sent to the exchanger 111 through the conduit 135. The pressure of the first refrigerant mixture at the outlet of the compressor 130 can be between 2 MPa and 4 MPa. The temperature of the first refrigerant mixture at the outlet of the condenser 131 can be between 30 ° C and 55 ° C. The first refrigerant mixture can be formed by a mixture of hydrocarbons such as a mixture of ethane and propane, but can also contain methane, butane and / or pentane. The proportions in molar fraction (%) of the components of the first refrigerant mixture can be:

Ethane: 30% to 70% Propane: 30% to 70% Butane: 0% to 10% The natural gas coming from the exchanger 111 through the conduit 102 can be fractionated, that is to say that a part of the C ₂₊ hydrocarbons containing at least two carbon atoms is separated from the natural gas, using a device known from one skilled in the art. The fractionated natural gas is sent via line 102 to the exchanger 112. The collected C ₂₊ hydrocarbons are sent to fractionation columns comprising a deethanizer. The light fraction collected at the top of the deethanizer can be mixed with the natural gas circulating in the conduit 102. The liquid fraction collected at the bottom of the deethanizer is sent to a depropanizer. The gas circulating in the conduit 102 and the second refrigerant mixture circulating in the conduit 124 enter the exchanger 112 to circulate there in parallel and co-current directions. The second refrigerant mixture leaving the exchanger 112 through the conduit 125 is expanded by the expansion device 122. The expansion device 122 may be a turbine, a valve or a combination of a turbine and a valve. The second expanded refrigerant mixture from the expansion device 122 is sent to the exchanger 112 to be vaporized by circulating against the flow of natural gas and the second refrigerant mixture. At the outlet of the exchanger 112, the second vaporized refrigerant mixture is compressed by the compressor 120 and then cools in the indirect heat exchanger 121 by heat exchange with an external cooling fluid, for example water or air. The second refrigerant mixture from the exchanger 121 is sent into the exchanger 111 through the conduit 123. The pressure of the second refrigerant mixture at the outlet of the compressor 120 can be between 2 MPa and 6 MPa. The temperature of the second refrigerant mixture at the outlet of the exchanger 121 can be between 30 ° C and 55 ° C. In the process described with reference to Figure 4, the second refrigerant mixture is not split into separate fractions, but, to optimize approach in the exchanger 112, the second refrigerant mixture can also be separated into two or three fractions, each fraction being expanded to a different pressure level, then sent to different stages of the compressor 120. The second refrigerant mixture is formed by for example by a mixture of hydrocarbons and nitrogen such as a mixture of methane, ethane and nitrogen but may also contain propane and / or butane. The proportions in molar fraction (%) of the components of the second refrigerant mixture can be: Nitrogen: 0% to 10%

Methane: 30% to 70% Ethane: 30% to 70% Propane: 0% to 10% Natural gas leaves liquefied from the heat exchanger 112 through line 103 at a pressure identical to the inlet pressure of natural gas , except for pressure losses. For example, the natural gas leaves the exchanger 112 at a pressure between 1 MPa and 15 MPa, preferably between 4 MPa and 7 MPa. This pressurized liquefied natural gas is expanded by the expansion device 113 to a pressure close to atmospheric pressure. The liquid natural gas obtained is evacuated through line 104.

The process shown diagrammatically in FIG. 5 represents a particular embodiment of the invention. The process shown schematically in FIG. 5 is identical to the process shown schematically in FIG. 4, except that according to the process in FIG. 5, an additional thermo-acoustic refrigeration apparatus 105 is placed on the conduit 103. In FIG. 5, the thermo-acoustic refrigeration apparatus 105 cools the fluid obtained at the outlet of the exchanger 112 by the conduit 103. The refrigeration apparatus 105 operates a cooling of the fluid of a value between 1 ° C. and 20 ° C, preferably between 1 ° C and 5 ° C.

The process shown diagrammatically in FIG. 6 represents a particular embodiment of the invention. The process shown schematically in FIG. 6 is identical to the process shown schematically in FIG. 4, except that according to the process in FIG. 6, an additional thermo-acoustic refrigeration apparatus 126 is placed on the duct 125. In FIG. 6, the thermo-acoustic refrigeration appliance 126 cools the second refrigerant mixture obtained at the outlet of the exchanger 112 by the conduit 125. The refrigeration appliance 126 operates a cooling of the fluid by a value between 1 ° C and 20 ° C, preferably between 1 ° C and 5 ° C.

The process shown diagrammatically in FIG. 7 represents a particular embodiment of the invention. The process shown schematically in FIG. 7 is identical to the process shown schematically in FIG. 4, except that according to the process in FIG. 7, an additional thermo-acoustic refrigeration apparatus 105 is placed on the conduit 103, and a refrigeration apparatus additional thermoacoustic 126 is disposed on the conduit 125. In FIG. 7, the thermo-acoustic refrigeration apparatus 105 cools the fluid obtained at the outlet of the exchanger 112 by the conduit 103, the thermo-acoustic refrigeration apparatus 126 cools the second refrigerant mixture obtained at the outlet of the exchanger 112 through the conduit 125. Apparatuses 105 and 112 cool down between 1 ° C and 20 ° C, preferably between 1 ° C and 5 ° C.

The operation of the methods described in relation to FIGS. 4, 5, 6 and 7 is illustrated by the numerical examples given below. For the processes of FIGS. 4 to 7, the natural gas arrives via the pipe 101 at a flow rate of 40,000 kmol / hour (695 tonnes / hour) at the temperature of 30 ° C and at the pressure of 5 MPa. The gas volume composition is 92% methane, 6% ethane, 1.5% propane and 0.5% nitrogen.

According to the process shown diagrammatically in FIG. 4, the gas obtained in line 103 is liquefied and cooled to the pressure of 4.85 MPa and to the temperature of - 163.5 ° C., so as to be completely liquid after expansion at storage pressure. The two cascade refrigerant mixing cycles allow this temperature to be obtained. The total compression power required is 194.4 MW (97.2 MW out of 120 and 130). For example, for each refrigerant mixing cycle, the compressors are driven by an 82 MW gas turbine and a 15.2 MW coupled motor. Compared to the process according to FIG. 4, according to the process shown diagrammatically in FIG. 5, a thermo-acoustic cooling device 105 is placed on the duct 103 before the expansion device 113. This device 105 makes it possible to provide a cooling power of 2 MW, thus cooling the 695 tonnes / hour of natural gas from -160.5 ° C to -163.5 ° C. Thus, if the same natural gas flow rate as in the example relating to FIG. 4 is maintained, the temperature of the natural gas leaving the exchanger 112 can be increased to -160.5 ° C. Consequently, the thermo-acoustic apparatus 105 makes it possible to reduce the compression power required by the two cycles of refrigerant mixture to 186.4 MW. Alternatively, if the same compression power is maintained as in the example illustrating the method of FIG. 4, the flow rate of liquefied natural gas obtained in the conduit 104 is increased by 4.3%. Compared to the process according to FIG. 4, according to the process shown diagrammatically in FIG. 6, a thermo-acoustic cooling device 126 is placed on the duct 125 before the expansion device 122. This device 126 makes it possible to lower the temperature of the second cooling mixture with a value of 2.4 ° C, thanks to a heat output of 2 MW. Thus, if the same natural gas flow rate is kept as in the example relating to FIG. 4, the pressure of the second refrigerant fluid at the outlet of the expansion device 122, that is to say the pressure at the inlet of the compressor 120, can be increased by 0.03 MPa. Consequently, the apparatus 126 makes it possible to reduce the compression power to 186.7 MW. Alternatively, if the same compression power is maintained as in the example illustrating the method of FIG. 4, the flow rate of liquefied natural gas obtained in the conduit 104 is increased by 4.2%.

Compared to the process according to FIG. 4, according to the process shown diagrammatically in FIG. 7, a thermo-acoustic cooling device 126 is placed on the duct 125 before the expansion device 122, and a thermo-acoustic cooling device 105 is placed on the conduit 103 before the expansion device 113. The apparatus 126 makes it possible to lower the temperature of the second refrigerant mixture by 2.4 ° C, thanks to a calorific power of 2 MW. Thus, if the same natural gas flow rate is kept as in the example relating to FIG. 4, the pressure of the second refrigerant fluid at the outlet of the expansion device 122, that is to say the pressure at the inlet of the compressor 120, can be increased by 0.03 MPa. Apparatus 105 provides power 2 MW of refrigeration, thus cooling the 695 tonnes / hour of natural gas from -160.5 ° C to -163.5 ° C. Thus, the temperature of the natural gas leaving the exchanger 112 can be increased to -160.5 ° C. Consequently, the thermo-acoustic devices 105 and 126 make it possible to reduce the compression power required by the two cycles of refrigerant mixing to 178.7 MW. Alternatively, if the same compression power is maintained as in the example illustrating the method of FIG. 4, the flow rate of liquefied natural gas obtained in line 104 is increased by 8.8%. 61 tonnes / hour of additional LNG are produced compared to the process according to FIG. 4.

The digital example illustrating the process according to FIG. 7 demonstrates the advantage of the invention compared to the two liquefaction modes which are the conventional liquefaction by heat exchange with two refrigerants (process described in relation to FIG. 4) and thermoacoustic liquefaction. Indeed, a thermoacoustic liquefaction of 4 MW, for example two modules of 2 MW, makes it possible to produce approximately 17 tonnes / hour of LNG. On the other hand, the 4 MW thermoacoustic liquefaction (two 2 MW modules) combined with a conventional liquefaction unit allows an additional production of 61 tonnes / hour.

Conventional natural gas liquefaction units have good yields, thanks to optimizations carried out over many years. However, the sizes of gas turbines capable of driving the compressors are few, and the LNG production capacity of the liquefaction unit is often fixed according to these gas turbines. In addition, the axial compressors are few, the size of the centrifugal compressors is limited by the admissible speed at the blade tip. These limitations make the production capacities of liquefaction units very inflexible, ie it is difficult to vary the flow rate of natural gas produced over time. In addition, temperature variations between summer and winter can cause a variation in uncontrollable production capacity, which can cause seasonal problems in supplying LNG customers. The method according to the invention makes it possible to easily adjust the production capacity of a unit for liquefying a natural gas. Indeed, the thermo-acoustic cooling devices being installed downstream of a valve, it is easy to have several, for example in parallel, with valves also in parallel. For example, with reference to Figure 1, the fluid arriving through line 2 is split into several streams. Each of these flows is cooled by a thermo-acoustic cooling device. Each of the cooled flows is expanded by a valve. Finally the expanded flows are combined to form the fluid flowing in the conduit 4, that is to say the natural gas liquefied at atmospheric pressure.

Currently, the yields of thermo-acoustic cooling devices are relatively low. However, it may be thought that the efficiency of these equipments, not yet used in the field of liquefaction of natural gas, could be considerably improved as they are developed in the present process. A low efficiency, therefore a significant gas consumption on a small part of the liquefaction unit, by the thermo-acoustic cooling apparatus, is acceptable in a production site where the price of gas is very low. This additional gas consumption is all the more acceptable since the improvement in the total yield of the process according to the invention compared to a conventional liquefaction unit compensates for the low yield of the thermo-acoustic apparatus. In addition, the financial investment corresponding to thermo-acoustic refrigeration equipment is very low compared to the considerable price of a unit for liquefying natural gas. In addition, a thermo-acoustic refrigeration device is very compact, and therefore does not increase much the large areas required for the installation of a conventional liquefaction unit: for example, a thermoacoustic device with a power of 2 MW can fit in a circle 5 m in diameter.

The operating principle of a thermo-acoustic cooling apparatus, as used in the invention, is shown diagrammatically in FIG. 8. The principle of a thermoacoustic apparatus consists in producing cold from "raw heat" ”, Using the properties of the so-called“ thermo-acoustic ”phenomena which are thermal exchange and energy conversion phenomena in the contact zones, also called thermal boundary layer, between a solid and a liquid. In general, the thermo-acoustic apparatus has three parts. The heat engine 43 is used to generate an acoustic wave. The heat engine 43 is supplied with primary energy in the form of heat admitted by the flow 51. A large thermal gradient is created between an area heated by the flow 51 and an area cooled by a fluid at ambient temperature arriving through the conduit 63 and discharged through line 64. The refrigerant can be water. This thermal gradient makes it possible to generate, by thermo-acoustic phenomenon, an acoustic wave which is transmitted to the refrigerator 41 via a resonator 42. The resonator 42, for example, is formed from one or more closed tubes containing, for example, medium pressure helium. The acoustic wave is established within the or the tubes. A refrigerator 41 is arranged downstream of the resonator 42. The refrigerator 41 uses the energy of the acoustic wave to produce a cold spot at low temperature according to a thermo-acoustic conversion process. The fluid to be cooled at low temperature is introduced into the refrigerator 41 through the conduit 71, then is evacuated at a lower temperature through the conduit 72. The refrigerator 41 must evacuate heat using a fluid at room temperature arriving via line 61 and discharged through line 62. This fluid may be water. This fluid can also advantageously be a fluid obtained at a temperature close to or below 0 ° C. during the purification of natural gas, or of the refrigerant mixture of the first cycle of the liquefaction process.

The thermo-acoustic cooling devices used in the present invention can be developed from the prototypes described in the documents cited below.

• “Thermoacoustic Natural Gas Liquéfier” by RJ. Hanold and G.W. Swift Journal US DOE et al. Natur. Gas RDD Contract. Rev. Mtg. (Baton Rouge, LA, 4 / 4-6 / 95) Proc. 2 506-511 (April 1995) Petroleum Abstracts ABSTR. NO. 637,273 V36 N.48 (11/30/96) ISSN: 0031-6423 • “Development of a thermoacoustic natural gas liquefaction” by G.W. Swift (Second topical conference on Natural Gas Utilization - AIChE Spring Meeting March 10-14, 2002)

• “A thermoacoustically driven puise tube refrigerator capable of working below 120 K” by T. Jin, G.B. Chen, Y. Shen Journal of Cryogénies v41, N ° 8 2001, P 595-601

• US 4,953,366.

Claims

1) Method for liquefying a gas, the gas being available under a pressure PI, in which the gas undergoes the following steps: the gas under pressure PI is condensed by heat exchange with a refrigerant so as to obtain a liquid under pressure PI, the refrigerant being vaporized during the heat exchange, and the liquid under pressure PI is expanded to a pressure P2, in which the refrigerant undergoes the following steps: the vaporized refrigerant is compressed, the compressed refrigerant, - the cooled refrigerant is expanded, the expanded refrigerant condenses the gas under pressure PI by heat exchange, in which at least one of the following two steps is carried out: - before expansion, it is sub-cooled the liquid under pressure PI by a first thermo-acoustic cooling device, - before expansion, the refrigerant cooled by a second is sub-cooled th thermo-acoustic cooling equipment.

2) Method according to claim 1, wherein the gas is a natural gas under a pressure between 1 MPa and 15 MPa and at a temperature between 20 ° C and 60 ° C.

3) Method according to one of claims 1 and 2, wherein the first thermo-acoustic cooling apparatus lowers the temperature of the cooled liquid by a value between 1 ° C to 20 ° C. 4) Method according to one of claims 1 to 3, wherein the second thermo-acoustic cooling apparatus lowers the temperature of the cooled refrigerant by a value between 1 ° C to 20 ° C.

5) Method according to one of claims 1 to 4, wherein the thermo-acoustic cooling devices comprise: a heat engine supplied with heat, which generates an acoustic wave, - a resonator in which the thermo-acoustic wave is established. acoustic, a refrigerator, placed downstream of the resonator, using the energy of the acoustic wave to produce a cold spot at low temperature. 6) Method according to one of claims 1 to 5, wherein the pressurized liquid PI is sub-cooled by several thermo-acoustic cooling devices arranged in parallel.

7) Method according to one of claims 1 to 6, wherein the cooled refrigerant is sub-cooled by several thermo-acoustic cooling devices arranged in parallel.