COOLING DEVICE FOR GAS LIQUEFACTION PLANT

Abstract

The present invention teaches a cooling device (1) for a gas liquefaction plant, comprising a gas liquefier (7), the device comprising at least three independent cascaded cooling circuits (10, 20, 30). The high-temperature cooling circuit (10) comprises at least one compressor (C101) and an associated condenser (E102), while the medium (20) and low (30) temperature cooling circuits each comprise at least two compression stages (C201, C202, C301, C302) and an associated condenser (E205-1, E205-2, E305-1, E305-2), respectively. [Fig. 1]

Description

Title of the invention: COOLING DEVICE FOR A GAS LIQUEFACTION PLANT Technical field

[0001] The invention relates to a cooling device intended for a gas liquefaction installation, such as natural gas or biomethane, of the type comprising a gas liquefier into liquefied gas. Technical background

[0002] Gas liquefaction installations, such as natural gas or biomethane, make it possible to liquefy a gas at a temperature of around -160°C so that the transport of the gas thus liquefied takes place at a pressure of around 1.2 bar, i.e. slightly higher than atmospheric pressure. Currently, several technologies for cooling devices connected to such a liquefier of the installation exist. For example, the cooling device described in document EP20305455 is known in which two or three cooling stages are mounted in cascade.

[0003] Although such cooling devices make it possible to reduce manufacturing and maintenance costs, these cooling devices still implement complex cycles to achieve liquefaction and therefore have non-optimized energy yields. In particular, the compressors they implement require significant compression powers which locally cause very significant heat exchanges. Statement of the invention

[0004] An aim of the invention is to provide a cooling device for a gas liquefaction installation which solves the above technical problems, in particular which makes it possible to locally reduce the quantity of heat produced and increase the exegetical efficiency.

[0005] To this end, a cooling device is provided for a gas liquefaction installation, comprising a gas liquefier, the device comprising at least three independent cooling circuits in cascade, including at least:

[0006] - a low temperature cooling circuit intended to be fluidly connected- specifically to the gas liquefier;

[0007] - a medium temperature cooling circuit connected to the cooling circuit low temperature cooling via at least a first heat exchanger so as to extract calories from the low temperature cooling circuit during operation; and

[0008] - a high temperature cooling circuit connected to the cooling circuit medium temperature cooling via at least a second heat exchanger so as to extract calories from the medium temperature cooling circuit during operation;

[0009] the high temperature cooling circuit comprising at least one compressor and an associated condenser, the medium and low temperature cooling circuits respectively comprising at least two compression stages and an associated condenser.

[0010] Advantageously, but optionally, the cooling device according to the invention has at least one of the following technical characteristics:

[0011] - the stages of the at least two compression stages of the cooling circuit medium temperature are connected in series; and / or - the stages of the at least two compression stages of the low temperature cooling circuit are connected in series;

[0012] - at least one of the at least two compression stages of the cooling circuit medium temperature cooling circuit comprises at least one pre-cooler downstream of the compressor and upstream of the associated condenser, preferably two pre-coolers; and / or - at least one of the at least two compression stages of the low temperature cooling circuit comprises at least one pre-cooler downstream of the compressor and upstream of the associated condenser, preferably two pre-coolers;

[0013] - the first heat exchanger comprises at least one heat exchanger forming a condenser of the low temperature cooling circuit and an evaporator of the medium temperature cooling circuit, preferably the first heat exchanger comprises two heat exchangers connected in parallel; and / or - the second heat exchanger comprises a heat exchanger forming a condenser of the medium temperature cooling circuit and an evaporator of the high temperature cooling circuit, preferably the second heat exchanger comprises two heat exchangers connected in parallel;

[0014] - the low temperature cooling circuit comprises a first bottle fluidly connected liquid between the stages of the at least two compression stages; and / or - the medium temperature cooling circuit comprises a second fluidly connected liquid bottle downstream of the second heat exchanger and upstream of the first heat exchanger; and / or - the high temperature cooling circuit comprises a third fluidly connected liquid bottle downstream of the associated condenser and downstream of the second heat exchanger;

[0015] - the low temperature cooling circuit comprises a first bottle anti-knock fluidically connected downstream of the gas liquefier and upstream of the at least two compressor compression stages; and / or - the medium temperature cooling circuit comprises a second anti-knock bottle fluidically connected downstream of the associated condenser and upstream of the at least two compressor compression stages; and / or - the high temperature cooling circuit comprises a third anti-knock bottle fluidically connected downstream of the associated condenser and upstream of the compressor;

[0016] - the low temperature cooling circuit comprises first means of oil separation downstream of the at least two compression stages; and / or - the medium temperature cooling circuit comprises second oil separation means downstream of the at least two compression stages; and / or - the high temperature cooling circuit comprises third oil separation means downstream of the compressor;

[0017] - each of the first means and / or the second means and / or the third means comprises a first oil separator, preferably each of the first means and / or the second means and / or the third means further comprises a second oil separator;

[0018] - further comprising a group generating a cold fluid connected to at least condenser of at least one of the low, medium and high temperature cooling circuits;

[0019] - further comprising an air heater unit connected to at least one condenser of at least at least one of the low, medium and high temperature cooling circuits;

[0020] - the low temperature cooling circuit comprises a fluid characterized by: - a low pressure (LP) evaporation pressure higher than atmospheric pressure; - a high pressure (HP) and low pressure (LP) ratio for each compression stage of the thermodynamic cycle which is less than 8; - the saturation temperature of the low pressure (LP) is lower than the condensation temperature of the fluid of the gas liquefier to be cooled; and - the condensation temperature is higher than the return temperature of a cold cooling fluid; preferably the fluid of the low temperature cooling circuit is methane;

[0021] - the medium temperature cooling circuit (20) comprises a fluid ca characterized by: - ​​a low pressure (LP) evaporation pressure higher than atmospheric pressure; - a high pressure (HP) and low pressure (LP) ratio for each compression stage of the thermodynamic cycle which is less than 8; - the saturation temperature of the low pressure (LP) is lower than the condensation temperature of the fluid in the low temperature cooling circuit; and - the condensation temperature is higher than the evaporation temperature of a fluid in the high temperature cooling circuit; preferably the fluid in the medium temperature cooling circuit is ethylene.

[0022] - the high temperature cooling circuit (10) comprises a fluid characterized by: - ​​a low pressure (LP) evaporation pressure higher than atmospheric pressure; - a high pressure (HP) and low pressure (LP) ratio for each compression stage of the thermodynamic cycle which is less than 8; - the saturation temperature of the low pressure (LP) is lower than the condensation temperature of the fluid in the medium temperature cooling circuit; and - the condensation temperature is higher than the evaporation temperature of a fluid in the high temperature cooling circuit; preferably the fluid in the high temperature cooling circuit is propylene.

[0023] Also provided is a container, such as a shipping container, comprising the device. Brief description of the figures

[0024] Other features and advantages of the invention will become apparent upon reading the description and examples of the invention. [Fig. 1] is a diagram of an example of implementation of a cooling device according to the invention. [Fig. 1] also serves as a support for examples of the generalized invention.

[0025] Detailed description of the three embodiments

[0026] With reference to [Fig.l], we will discuss examples of a cooling device 1 for a gas liquefaction plant 6. The gas liquefaction plant 6 comprises a liquefier 7 at the inlet of which a non-liquefied gas 61 is introduced and at the outlet of which a liquefied gas 62 is extracted for storage. On the other hand, the liquefier 7 has an outlet 71 and an inlet 72. The outlet 71 and inlet 72 are intended to be fluidically connected to the cooling device 1.

[0027] The gas liquefaction installation 6 may take the form of an ATEX zone 6 -ATEX is the acronym for ATmosphère Explosive-; typically in a situation in which the gas to be liquefied is flammable and / or explosive, for example the gas to be liquefied is natural gas or biomethane. It will be understood that the cooling device 1 may be fluidically connected to any type of gas liquefier and to any type of liquefaction installation.

[0028] As illustrated in [Fig.l], the cooling device 1 according to the invention can be located outside the ATEX zone 6 of the gas liquefaction plant. This is made possible because the gas liquefaction plant 6 is fluidically connected to the cooling device via the outlet 71 and the inlet 72 of the liquefier 7.

[0029] In examples, the cooling device 1 according to the invention is included in a container. A container is a box of standardized dimensions which can be used for handling, storing or transporting materials or batches of objects. which simplifies packaging. For example, the container in which the cooling device is placed can be a maritime transport container as standardized in ISO 668:2020 and ISO 1496-3. This makes the cooling device easily transportable and can be installed away from an ATEX zone.

[0030] The cooling device according to the invention comprises a series of independent cooling circuits positioned in cascade comprising at least three cooling circuits: a high-temperature cooling circuit 10, a medium-temperature cooling circuit 20 and a low-temperature cooling circuit 30. The basic principle of the cooling device 1 according to the invention is that, during operation, the low-temperature cooling circuit 3 extracts the calories from the liquefier 7 by being fluidically connected to the outlet 71 and inlet 72 of the liquefier 7. For its part, still during operation, the medium-temperature cooling circuit 20 extracts the calories from the low-temperature cooling circuit 30 via at least one first heat exchanger E305-1 or E305-2 so as to extract the calories from the low-temperature cooling circuit.Finally, still during operation, the high temperature cooling circuit 10 extracts the calories from the medium temperature cooling circuit 20 via at least one second heat exchanger E205-1, E205-2 so as to extract the calories from the medium temperature cooling circuit. The three cooling circuits 10, 20, 30 are independent and are in series with each other, while being in cascade. In cascade means that the device consists of a succession of thermodynamic installations 10, 20, 30 and that these installations include refrigeration circuits which use refrigerants working at different temperature levels and thermally coupled by an exchanger.

[0031] Each cooling circuit of the device according to the invention comprises a refrigerant (or also called a refrigerant) and means for compressing this refrigerant and a condenser associated with the circuit, according to the refrigeration cycle. More precisely, the high-temperature cooling circuit comprises at least one (at least one) compression stage, and the medium and low-temperature circuits comprise at least two (at least two) compression stages. A compression stage is a part of the circuit which comprises at least one compressor compression means.

[0032] The presence of at least two compression stages on the medium and low temperature circuits 20, 30 improves the distribution of the work provided by the compressors as well as the dissipation of the heat produced during compression. This makes it possible to reduce the temperatures at the outlet of the compressors and this makes it possible also to operate within the permissible temperature ranges of the compressors. Particularly for the medium and low temperature cooling circuits because the temperatures of their refrigerants must be very low for liquefaction to operate at the outlet of liquefier 7. For example, biomethane will leave liquefier 7 in a saturated liquid state (LNG) at a pressure of 8 bars and a temperature of -128.74 °C. Thus, the two-stage compression for these two circuits results in a reduction in the individual power of each compressor as well as a reduction in local heat exchanges.

[0033] In examples, the compressors may be two-stage compressors and / or reciprocating compressors.

[0034] In examples, the stages of the at least two compression stages of the medium-temperature cooling circuit 20 are connected in series. This means that the compressors are located on the same branch of the cooling circuit.

[0035] In examples, the stages of the at least two compression stages of the low-temperature cooling circuit 30 are connected in series. Similarly, this means that the compressors are located on the same branch of the circuit.

[0036] In the example of [Fig. 1], the compressor C301 of the first compression stage and the compressor C302 of the second compression stage of the low temperature cooling circuit are connected in series. Still in [Fig.l], the compressor C201 of the first compression stage and the compressor C202 of the second compression stage of the medium temperature cooling circuit are also connected in series.

[0037] The high temperature cooling circuit is now discussed according to several examples, including the example of [Fig.l]. These examples combine with each other.

[0038] In these examples, and as already discussed, the high-temperature cooling circuit 10 is connected to the medium-temperature cooling circuit 20 via at least one second heat exchanger E205-1 E205-2 so as to extract the calories from the medium-temperature cooling circuit during operation of the device. In addition, the high-temperature cooling circuit 10 comprises at least one compressor C101 and one and one associated condenser E102. The high-temperature cooling circuit 10 may further comprise a desuperheater E101.

[0039] In examples, the high-temperature cooling circuit 10 comprises, in the direction of circulation of a first refrigerant fluid illustrated by the arrows in the figure, a compressor C101 downstream of which a separator F101, here forming third separation means, is positioned so as to separate any impurities (typically oil droplets resulting from the operation of the compressor C101) from the first refrigerant fluid. The impurities (typically the oil from the compressor) extracted by the separator F101 can be returned to the compressor C101 via the line FC 101.

[0040] In examples, downstream of the separator F101, the high-temperature cooling circuit 10 comprises at least one desuperheater E101, for example in the form of a heat exchanger, which makes it possible to extract the calories from the high-temperature cooling circuit 10 to the outside of the cooling device 1 according to the invention. In the example of [Fig.l], the high-temperature cooling circuit 10 comprises at least one condenser E102, for example in the form of a heat exchanger, which also makes it possible to extract the calories from the high-temperature cooling circuit 10 to the outside of the cooling device 1 according to the invention.

[0041] The condenser of the cooling circuit (the desuperheater E101 and the condenser E102 in [Fig.l]) is connected to a cooling source in order to extract the calories from the refrigerant fluid of the high-temperature cooling circuit 10. In examples, the cooling source (the refrigerant) is a fluid selected from water, glycolated water or a gas such as, for example, air.

[0042] In the example of [Fig.l], the desuperheater E101 allows the flow to be cooled to ambient temperature, for example between 35 and 55°C. The second exchanger E102 is used to condense the flow, for example between 2 and 15°C. The desuperheater E101 uses air to cool the refrigerant of the high-temperature cooling circuit 10, and the second exchanger E102 uses glycolated water to cool the refrigerant of the high-temperature cooling circuit 10. It is understood that the desuperheater E101 and the condenser E102 could both use the same cooling source, for example water, glycolated water or even air. Or that the first exchanger E101 uses glycolated water and the second exchanger E102 uses air. Generally, any known means of condensing the first refrigerant can be used.

[0043] In examples, downstream of the condenser, the high-temperature cooling circuit 10 comprises an expansion valve TCV101. The refrigerant having undergone condensation, expansion or expansion is produced at the expansion valve to subsequently recover its cold energy during its evaporation in order to condense the refrigerant of the medium-temperature cooling circuit in the heat exchanger.

[0044] In examples, the high-temperature cooling circuit 10 comprises a liquid bottle TK101 fluidly connected downstream of the condenser associated with this circuit and upstream of the compressor C101 or upstream of the evaporator E205. In the example of [Fig.l], the liquid bottle or liquid reservoir TK101 is connected downstream of the condenser associated with this circuit and upstream of the expansion valve TCV101. In the examples, the liquid bottle TK101 forms a regulating reservoir for the first refrigerant; this liquid reservoir TK101 makes it possible to manage the charge of the first refrigerant according to the thermal load at the evaporator.

[0045] In examples, the high-temperature cooling circuit 10 comprises a liquid surge bottle TK-102. The role of the liquid surge bottle is to protect the compressor from possible migration of liquid through the suction line which would cause irreversible damage. The liquid surge bottle TK102 can also ensure the re-evaporation of the trapped liquid. In the example of [Fig.l], the liquid surge bottle TK102 is connected downstream of the condenser associated with the medium-temperature cooling circuit and upstream of the compressor C101.

[0046] The medium temperature cooling circuit is now discussed according to several examples, including the example of [Fig.l]. These examples combine with each other.

[0047] In these examples, and as already discussed, the medium temperature cooling circuit 20 comprises, in the direction of circulation of a second refrigerant fluid, which is associated with it, illustrated by the arrows in the figure, at least two compression stages where each compression stage comprises at least one compressor 201 202. The medium temperature cooling circuit comprises at least one condenser which is associated with it.

[0048] In the example of [Fig.l], the medium temperature cooling circuit comprises two compression stages which are connected in series, and each compression stage comprises a compressor C201, C202.

[0049] In examples, at least one compression stage of the medium-temperature cooling circuit 20 comprises at least one pre-cooler which makes it possible to cool the flow. It is understood that each stage can comprise at least one pre-cooler. In the example of [Fig.l], each compression stage comprises a compressor downstream of which are located two condensers which are pre-coolers. Thus, the first compression stage comprises the compressor C201 and the coolers (or pre-coolers) E201, E202; and the second compression stage comprises the compressor C202 and the coolers (or pre-coolers) E203, E204. The coolers (or pre-coolers) make it possible to dissipate the heat using a cooling source (the refrigerant) which is a fluid selected for example from water, glycolated water or a gas such as for example air.The presence of the first pre-cooler upstream of the heat exchanger E205-1 E205-2 makes it possible to considerably increase the efficiency of the medium temperature cooling circuit 20. .

[0050] In examples, the medium temperature cooling circuit comprises oil separation means (F202, F203) downstream of the at least two compression stages. The separation means make it possible to remove from the refrigerant fluid elements (impurities) which have been introduced by the compressors. The compressors used may be oil-lubricated piston compressors and this oil solidifies at a certain temperature (for example around -57°C). A small quantity of this oil may be present in the refrigerant circuit and constitute a risk when the temperature of the refrigerant falls below the solidification temperature of this oil. Still in these examples, the separation means comprises a separator F-202, preferably this separator is located at the outlet of the second compression stage. In examples, the separation means comprise a second separator F203.This second separator can be located at the outlet of the two compression stages; this last separation can be carried out after the E204 heat exchanger, in order to purify the refrigerant from the oil as much as possible before the temperature drops further.

[0051] In the example of [Fig.l], the compressors are oil-lubricated piston compressors. The first separator F202 is located downstream of the compressor C202 and upstream of the two pre-coolers E203, E204. The second separator F203 is located downstream of the pre-cooler E204 and upstream of the second heat exchanger E205-1, E205-2. The separation means can return the impurities (typically the compressor oil) thus extracted to the compressor C202 via a pipe and / or compressor C101 via a pipe.

[0052] In examples, the heat exchanger E205-1, E205-2 of the medium temperature cooling circuit comprises a heat exchanger forming a condenser of the medium temperature cooling circuit 20 and an evaporator of the high temperature cooling circuit 10. Thus, the condenser / evaporator E205-1 E205-2 forms, in these examples, means for extracting calories thermally connecting the medium temperature cooling circuit 20 to the high temperature cooling circuit 10.

[0053] In examples, the heat extractors (or evapocondensers) E205-1, E205-2 of the medium temperature cooling circuit comprise two heat exchangers which are mounted in parallel. Only one extractor is operating and the other is on standby or undergoing maintenance or cleaning.

[0054] In examples, the medium-temperature cooling circuit 20 comprises a liquid bottle TK202 fluidly connected fluidly between the second heat exchanger E205-1, E205-2 and upstream of the first heat exchanger E305-1, E305-2. In the examples, the liquid bottle TK202 forms a regulating reservoir for the second refrigerant; this liquid reservoir TK202 makes it possible to manage the charge of the second refrigerant as a function of the thermal load at the inlet of the first heat exchanger E305-1 E305-2.

[0055] In examples, the medium-temperature cooling circuit 20 comprises an expansion valve TCV201, for example an electronic expansion valve. The second refrigerant having undergone condensation, an expansion or expansion is carried out at the expansion valve to subsequently recover the cold energy from the evaporation of the second refrigerant in order to condense the refrigerant of the low-temperature cooling circuit in the heat exchanger (in examples the evaporator / condenser E305:1 / 2). In the example of [Fig.1], the liquid bottle TK202 is upstream of the expansion valve TCV201.

[0056] In examples, the medium-temperature cooling circuit 20 comprises a buffer tank TK201 fluidly connected between two compression stages. In the example of [Fig.l], the buffer tank TK201 is connected downstream of the pre-cooler E202 and upstream of the compressor C202. In the examples, the buffer tank TK201 forms a regulating tank for the second refrigerant fluid making it possible to dampen pressure fluctuations at the outlet of the first compression stage; this buffer tank TK201 makes it possible to manage the liquid load as a function of the compression and the thermal load at the pre-coolers E201 E202.

[0057] In examples, the medium temperature cooling circuit 20 comprises a liquid surge bottle TK203 fluidly connected downstream of the heat exchanger E305-1 E305-2 of the low temperature cooling circuit and upstream of the at least two compressor compression stages C201 C202. The role of the liquid surge bottle is to protect the compressor from possible migration of liquid through the suction line which would cause irreversible damage. The liquid surge bottle TK-203 can also ensure the re-evaporation of the trapped liquid. In the example of [Fig.l], liquid surge bottle TK203 is connected downstream of the condenser associated with the low temperature cooling circuit and upstream of the compressor C201.

[0058] In examples, the medium temperature cooling circuit 20 further comprises a safety circuit composed of two mechanical overflow valves PCV202 and PCV203, a storage volume TK204 and a mechanical expansion valve PCV204. The mechanical overflow valve PCV202 opens when the high pressure of the medium temperature cooling circuit increases above the safety pressure, for example when the pressure in the circuit exceeds 16 bar. On the other hand, the mechanical overflow valve PCV203 opens if the low pressure of the medium temperature cooling circuit increases above the safety limit, for example above 16 bar. When the overflow valve opens, the fluid is directed into the tank TK204 so that the pressure in the TK204 tank can increase until it reaches a pressure threshold, for example 15 bars, the PCV204 expansion valve opens when the compressor suction pressure is lower than the limit. This circuit operates mainly during system start-up or in the event of an unexpected increase in the low or high pressures of the circuit. The role of the TK204 tank is to prevent overpressures due to the evaporation of the second refrigerant circulating within the medium temperature cooling circuit 20 and thus protect the operation of said medium temperature cooling circuit 20. In addition, the TK204 tank makes it possible to reduce the quantity of refrigerant within the associated cooling circuit (here, the medium temperature cooling circuit 20).In addition, the TK204 tank allows the quantity of refrigerant to be regulated within the associated cooling circuit: in fact, when the pressure increases at the outlet of the C202 compressor, the excess refrigerant is sent to the TK204 tank through the PCV202 expansion valve and, conversely, in the event of a drop in pressure within the cooling circuit, an injection of refrigerant is carried out from the TK204 tank through the PCV204 expansion valve.

[0059] The low temperature cooling circuit is now discussed according to several examples, including the example of [Fig. 1]. These examples combine with each other.

[0060] The low temperature cooling circuit 30 has a structure similar to the medium temperature cooling circuit 20 described above.

[0061] The low-temperature cooling circuit 30 comprises, in the direction of circulation of a third refrigerant fluid, which is associated with it, illustrated by the arrows in the figure, at least two compression stages where each compression stage comprises at least compressor C301 C302. The low-temperature cooling circuit 30 comprises at least one condenser E305-1 E305-2 which is associated with it.

[0062] In examples, at least one compression stage of the low-temperature cooling circuit 30 comprises at least one pre-cooler which makes it possible to cool the flow. It is understood that each stage can comprise at least one pre-cooler. In the example of [Fig.l], each compression stage has a compressor downstream of which are located two pre-coolers. Still in the example of [Fig.l], four pre-coolers are associated with said medium-temperature cooling circuit. Thus, the first compression stage comprises the compressor C301 and the pre-coolers E301, E302; and the second compression stage comprises the compressor C302 and the pre-coolers E303, E304. The pre-coolers make it possible to dissipate the heat using a cooling source (the refrigerant) which is a fluid selected for example from water, glycolated water or a gas such as for example air.The presence of the first pre-cooler upstream of . the heat exchanger (or condensers) E305-1 E305-2 makes it possible to considerably increase the efficiency of the low temperature cooling circuit 30.

[0063] In examples, the low-temperature cooling circuit 30 comprises oil separation means (F302, F303) downstream of the at least two compression stages. The separation means make it possible to remove from the refrigerant fluid elements (impurities) which have been introduced by the compressors. The compressors used may be oil-lubricated compressors and this oil solidifies at a certain temperature (for example around -57°C). A small quantity of this oil may be present in the refrigerant circuit and constitute a risk when the temperature of the refrigerant falls below the solidification temperature of this oil. Still in these examples, the separation means comprises a separator F302, preferably this separator is located at the outlet of the second compression stage. In examples, the separation means comprise a second separator F303.This second separator can be located at the outlet of the two compression stages; this last separation can be carried out after the E304 heat exchanger, in order to purify the refrigerant from the oil as much as possible before the temperature drops further.

[0064] In the example of [Fig.l], the compressors are oil-lubricated compressors. The first separator F302 is located downstream of the compressor C302 and upstream of the two pre-coolers E303, E304. The second separator F303 is located downstream of the pre-cooler E304 and upstream of the first heat exchanger (or condenser) E305-1, E305-2. The separation means can return the impurities (typically the compressor oil) thus extracted to the compressor C302 via a pipe and / or compressor C301 via a pipe.

[0065] In examples, the heat exchanger E305-1, E305-2 of the low-temperature cooling circuit comprises a heat exchanger forming a condenser of the low-temperature cooling circuit 30 and an evaporator of the medium-temperature cooling circuit 20. Thus, the condenser / evaporator E305-1 E305-2 forms, in these examples, means for extracting calories thermally connecting the medium-temperature cooling circuit 20 to the low-temperature cooling circuit 30.

[0066] In examples, the heat exchanger E305-1, E305-2 of the low temperature cooling circuit comprises two heat exchangers which are connected in parallel. Only one extractor is operating and the other is on standby or undergoing maintenance or cleaning (returning the oil to the compressors).

[0067] In examples, the low temperature cooling circuit 30 comprises a liquid bottle TK302 fluidly connected between the first heat exchanger E305-1, E305-2 and upstream of the expansion valve TCV301. In the examples, the TK302 expansion tank forms a regulating tank for the third refrigerant; this TK302 liquid tank allows the charge of the third refrigerant to be managed according to the thermal load at the inlet of the first heat exchanger E305-1 E305-2.

[0068] In examples, the low-temperature cooling circuit 30 comprises an expansion valve TCV301, for example an electronic expansion valve. The third refrigerant fluid having undergone condensation, expansion or expansion is carried out at the expansion valve to subsequently recover the cold energy from the evaporation of the third refrigerant fluid in order to liquefy the gas in the evaporator / condenser E4021 E4022 of the liquefier 7. In the example of [Fig.l], the liquid cylinder TK302 is upstream of the expansion valve TCV301.

[0069] In examples, the low-temperature cooling circuit 30 comprises a buffer tank TK301 fluidly connected between two compression stages. In the example of [Fig.l], the buffer tank TK301 is connected downstream of the pre-cooler E302 and upstream of the compressor C302. In the examples, the buffer tank TK301 forms a regulating tank for the third refrigerant; this liquid tank TK301 makes it possible to manage the fluctuation of the pressure at the outlet of the first compression stage.

[0070] In examples, the low-temperature cooling circuit 30 comprises a liquid-stab bottle TK303 fluidly connected downstream of the heat exchanger E305-1 E305-2 of the low-temperature cooling circuit and upstream of the at least two compressor compression stages C301 C302. The role of the liquid-stab bottle is to protect the compressor from possible migration of liquid through the suction line which would cause irreversible damage. The liquid-stab bottle TK303 can also ensure the re-evaporation of the trapped liquid. In the example of [Fig.l], the liquid-stab bottle TK303 is connected downstream of the condenser of the gas liquefier 7 and upstream of the compressor C101.

[0071] In examples, the low-temperature cooling circuit 30 further comprises a safety circuit composed of two mechanical overflow valves PCV302 and PCV303, a storage volume TK304 and a mechanical expansion valve PCV304. The mechanical overflow valve PCV302 opens when the high pressure of the low-temperature cooling circuit increases above the safety pressure, for example when the pressure in the circuit exceeds 31 bar. On the other hand, the mechanical overflow valve PCV-302 opens if the low pressure of the low-temperature cooling circuit increases above the safety limit, for example above 6 bar. When the overflow valve opens, the fluid is directed into the reservoir TK304 such that the pressure in the reservoir TK304 can increase until it reaches a pressure threshold, for example 15 bar; the expansion valve PCV304 opens when the pressure at the suction of compressor C301 is below the limit. This circuit operates mainly during system start-up or in the event of an unexpected increase in the low or high pressures of the circuit. The role of the TK304 tank is to prevent overpressures due to the evaporation of the third refrigerant circulating within the low-temperature cooling circuit 30 and thus to protect the operation of said low-temperature cooling circuit 30. In addition, the TK304 tank makes it possible to reduce the quantity of refrigerant within the associated cooling circuit (here, the low-temperature cooling circuit 30).In addition, the TK304 tank allows the quantity of refrigerant to be regulated within the associated cooling circuit: in fact, when the pressure increases at the outlet of the C302 compressor, the excess refrigerant is sent to the TK304 tank through the PCV304 expansion valve and, conversely, in the event of a drop in pressure within the cooling circuit, an injection of refrigerant is carried out from the TK304 tank through the PCV304 expansion valve.

[0072] In examples, the device according to the invention comprises a group generating a cold fluid connected to at least condensers (E102, E205-1, E205-2, E305-1, E305-2) of at least one of the low, medium and high temperature cooling circuits. The cold group can be used to cool a refrigerant liquid, for example water or glycolated water. Alternatively or additionally, the device according to the invention comprises an air heater group connected to at least condensers (E102, E205-1, E205-2, E305-1, E305-2) of at least one of the low, medium and high temperature cooling circuits. In the example of [Fig.l] , the desuperheater E101 and the condenser El02 or the two pre-coolers E201 and E202 or the two pre-coolers E203 and E204 or the two pre-coolers E301 and E302 or the two pre-coolers E303 and E304 are connected in series, the first condenser crossed by the refrigerant of the circuit is cooled by the air heater unit and the second condenser which is then crossed by the refrigerant of the circuit is cooled by the generator unit of a cold fluid. The joint use of air and water makes it possible to reduce the energy consumption compared to the case where only a generator unit of a cold fluid would be used, while guaranteeing the required cooling. In [Fig.l], the fluid cooled by the cold fluid generator group is glycolated water and is only connected to the condenser E102 as well as to the pre-cooler E202, E204, E302 and E304.

[0073] In examples, the low temperature cooling circuit (30) comprises a refrigerant that is characterized by (i) a low pressure (LP) evaporation pressure greater than atmospheric pressure, (ii) a high pressure (HP) to low pressure (LP) ratio for each compression stage of the thermodynamic cycle that is less than 8, (iii) a low pressure (LP) saturation temperature that is in lower than the condensation temperature of the gas liquefier fluid to be cooled, and (iv) a condensation temperature that is higher than the evaporation temperature of a medium-temperature cooling circuit fluid. In these examples, the low-temperature cooling circuit fluid may be methane.

[0074] In examples, the medium temperature cooling circuit (20) comprises a refrigerant that is characterized by (i) a low pressure (LP) evaporation pressure greater than atmospheric pressure, (ii) a high pressure (HP) to low pressure (LP) ratio for each compression stage of the thermodynamic cycle that is less than 8, (iii) a low pressure (LP) saturation temperature that is lower than the condensation temperature of the fluid in the low temperature cooling circuit, and (iv) a condensation temperature that is higher than the evaporation temperature of a fluid in the high temperature cooling circuit. In these examples, the fluid in the medium temperature cooling circuit may be ethylene.

[0075] In examples, the high temperature cooling circuit (30) comprises a refrigerant that is characterized by (i) a low pressure (LP) evaporation pressure greater than atmospheric pressure, (ii) a high pressure (HP) to low pressure (LP) ratio for each compression stage of the thermodynamic cycle that is less than 8, (iii) a low pressure (LP) saturation temperature that is lower than the condensation temperature of the fluid in the medium temperature cooling circuit, and (iv) a condensation temperature that is higher than the evaporation temperature of a fluid in the high temperature cooling circuit. In these examples, the fluid in the medium temperature cooling circuit may be propylene.

[0076] The examples presented of the low, medium and high temperature cooling circuits are combined with each other.

[0077] A particular example of implementation of [Fig. 1] is now presented. It will be understood that the examples or generalization or operating principles presented previously apply to this particular example of implementation.

[0078] The main biomethane circuit of the gas liquefaction plant 6 is shown. In this main biomethane circuit of the gas liquefaction plant 6, biomethane originating for example from a purification at 8 bar enters an electric heater to ensure a temperature of 40 °C before the flow undergoes liquefaction in the liquefier 7. The flow is then liquefied in the heat exchanger E402:1 / 2. Two heat exchangers E4021 and E4022 are connected in parallel. Only one heat exchanger operates while the other is stopped, for example during cleaning. The biomethane leaves the liquefier E402:1 / 2 in the saturated liquid state (LNG) at a pressure of 8 bar and at a temperature of approximately -128 °C. The liquid (LNG) can then be stored and / or used.

[0079] In this example of the main bio-methane circuit of the gas liquefaction installation 6, the thermodynamic cycle used includes in particular an electric heater E401, two evaporator-condensers (liquefiers) E-402:1 / 2 in parallel.

[0080] The low temperature refrigeration stage 30 of this implementation example is now presented. The objective of the low temperature stage is to liquefy the biomethane from the main biomethane circuit.

[0081] The refrigerant used in this stage is methane. The methane is compressed using a two-stage compression C301 and C302 from 5 to 30 bars. Two exchangers in series after each compression stage allow the flow to be cooled first using glycol water at 45 °C for the pre-coolers E301 and E303 in then to 8 °C using glycol water in the pre-coolers E302 and E304. A buffer tank TK301 is installed between the two compression stages.

[0082] The compressors used are oil-lubricated piston compressors. This oil solidifies at -57°C. A small amount of this oil may be present in the refrigerant circuit and constitute a risk when the refrigerant temperature drops below -57°C. Therefore, an oil separator F302 is first used at the outlet of the second compressor C302, to limit the amount of oil in the low-temperature circuit. A further separation is then carried out, and consists of a pre-separator and the main separator in series F303. This last separation is carried out after the heat exchanger E304, in order to purify the refrigerant as much as possible from the oil before the temperature drops further.

[0083] The methane from the low temperature circuit then passes through the evaporator / condenser E-305:l / 2. Two parallel heat exchangers E-305:l / 2 are installed for this purpose, in which only one heat exchanger is operating, and the other is on standby or undergoing maintenance or cleaning. The methane leaves this heat exchanger at a saturation liquid temperature of approximately -95°C. A liquid receiver TK302 is then installed which allows the liquid charge to be managed according to the thermal load at the evaporator. Afterwards, the refrigerant from the low temperature circuit undergoes expansion at a TCV301 expansion valve and leaves two-phase at the saturation temperature of the low pressure of the compressor. The low pressure is approximately 5 bar and the saturation temperature is approximately -137°C.The low pressure is chosen so that the low pressure stream can liquefy the main bio-methane stream and taking a minimum pinch of 5 °C in the liquefier. The low pressure stream is evaporated in the liquefier while the main bio-methane stream is liquefied. The evaporated stream then passes into a TK303 liquid anti-knock bottle to avoid any liquid drops at the compressors suction.

[0084] The low temperature refrigeration stage 30 comprises a safety circuit composed of two mechanical overflow valves PCV302 and PCV303, a storage volume of TK-304 and a mechanical expansion valve PCV304. The mechanical overflow valve PCV302 opens when the high pressure of the low temperature circuit increases above the safety pressure, which in this example is considered to be equal to 31 bars. On the other hand, the mechanical overflow valve PCV302 opens if the low pressure of the low temperature circuit increases above the safety limit, considered in this example equal to 6 bars. The flow in both cases is directed into the tank TK304. The pressure in the TK304 can increase up to 15 bars, and then the mechanical expansion valve PCV304 opens. This circuit operates primarily during system startup or in the event of an unexpected increase in low or high pressure in the low temperature cooling circuit.

[0085] In this example of the low temperature circuit, the thermodynamic cycle used contains two compressors: C301 and C302, an electronic expansion valve for the bypass of C301: PCV301, the intercoolers with glycolated water: E301, E302, E303, E304, a buffer tank: TK301, two oil separators: F302 and F303, two evaporator-condensers in parallel: E305:1 / 2, a liquid bottle: TK302, an electronic expansion valve: TCV301, two evaporator-condensers (liquefier) ​​in parallel: E402:1 / 2, a liquid shock bottle: TK303, two mechanical overflow valves: PCV302 and PCV303, a mechanical expansion valve: PCV304, a storage and safety volume: TK304.

[0086] The medium temperature refrigeration stage 20 of this implementation example is now presented. The purpose of the medium temperature stage is to condense the refrigerant from the low temperature stage (methane) in the E-305:1 / 2 heat exchanger.

[0087] The refrigerant used in this stage is ethylene. The ethylene is compressed using a two-stage compression (C201 and C202) from 1 to 15 bars. Two exchangers in series after each stage allow the flow to be cooled using glycolated water first at 45°C in E201 and E203 and then at 8°C in E202 and E204. A buffer tank TK201 is installed between the compressors.

[0088] The compressors used are oil-lubricated piston compressors. This oil solidifies at -57°C. A small amount of this oil may be present in the refrigerant circuit and constitute a risk when the refrigerant temperature drops below -57°C. Therefore, an oil separator F202 is first used at the outlet of the second compressor C202, to limit the amount of oil in the medium temperature circuit. A further separation is then carried out, and consists of a pre-separator and the main separator in series F203. This last separation is carried out after the heat exchanger E204, in order to purify the re- refrigerant oil before the temperature drops further.

[0089] The ethylene then passes through the evaporator / condenser E-205:1 / 2. Two parallel heat exchangers E205-1 and E205-2 are installed for this purpose, in which only one heat exchanger is operating and the other is on standby or undergoing maintenance or cleaning. The ethylene leaves this heat exchanger at a saturation liquid temperature of -38 °C. A liquid receiver TK202 is then installed which allows the liquid load to be managed according to the thermal load at the evaporator. Afterwards the fluid undergoes expansion at the expansion valve and leaves two-phase at the saturation temperature of the low pressure of the compressor; the low pressure is approximately 1 bar and the saturation temperature approximately -100 °C). The low pressure is chosen so that the medium temperature flow can condense the flow from the low pressure stage and taking a minimum pinch of 5 °C in the evaporator / condenser E305:l / 2.The medium temperature stream is evaporated in the evaporator / condenser while the low temperature stream is condensed at 30 bar for a saturation temperature of approximately -96°C. The evaporated stream then passes into a TK203 liquid surge suppressor to prevent any liquid drops at the compressor suction. Two parallel liquid surge suppressors are installed in the medium temperature circuit.

[0090] A safety circuit consisting of two mechanical overflow valves (PCV202 and PCV203, a storage volume TK204 and a mechanical pressure reducer PCV204. The mechanical overflow valve PCV202 opens when the high pressure of the medium temperature circuit increases above the safety pressure, for example equal to 16 bars. On the other hand, the PCV202 opens if the low pressure of the medium temperature circuit increases above the safety limit, for example equal to 2 bars. The flow in both cases is directed into the tank TK204. The pressure in the tank TK204 can increase up to 15 bars, then the pressure reducer PCV204 opens. This circuit operates mainly during system start-up or in case of an unexpected increase in the low or high pressures of the circuit.

[0091] In this example of the medium temperature circuit, the thermodynamic cycle used contains two compressors: C201 and C202, an Electronic Expansion Valve (for the bypass of C201): PCV201, intercoolers with glycolated water: E201, E202, E203, E204, a buffer tank: TK201, two oil separators: F202 and F203, two evaporator-condensers in parallel: E-205: 1 / 2, a liquid bottle: TK202, an electronic expansion valve: TCV201, two evaporator-condensers in parallel: E-305: 1 / 2, a liquid shock bottle: TK203, two mechanical overflow valves: PCV202 and PCV203, a mechanical expansion valve: PCV204, a storage and safety volume: TK204.

[0092] The high temperature refrigeration stage 10 of this exemplary implementation is now presented. The purpose of the high temperature stage is to condense the refrigerant from the medium temperature stage (ethylene) in the E205:l / 2 heat exchanger.

[0093] The refrigerant used in this stage is propylene. Propylene is compressed using a single-stage compression C101 from about 1 to 8 bar. Two exchangers in series after the compressor with glycol water are used. The first E101 allows the flow to be cooled to ambient temperature 45 °C. The second exchanger El02 is used to condense the flow to 8 °C. The temperature in this circuit does not fall below -44 °C. There is therefore no risk of solidification of the oil.

[0094] A TK101 liquid receiver is then installed which allows the liquid charge to be managed according to the thermal load at the evaporator. At the outlet of the liquid receiver the refrigerant passes through a filter drier to remove moisture from the circuit and the risk of making the oil acidic causes the degradation of the compressor. The fluid then undergoes expansion at the expansion valve and leaves two-phase at the saturation temperature of the low pressure of the compressor, for example the low pressure is approximately 1 bar for a saturation temperature of -43.0 °C.

[0095] The low pressure is chosen so that the flow from the high temperature circuit can condense the flow from the medium temperature stage and taking a minimum pinch of 5 °C in the evaporator / condenser E205:1 / 2. The high temperature flow is evaporated in the evaporator / condenser E-205:1 / 2 while the medium temperature flow MT is condensed at about 15 bars for a saturation temperature of about -38.0 °C. The evaporated flow then passes into a liquid shock bottle TK102 to avoid any liquid drops at the compressor suction.

[0096] In this example of the high temperature circuit, the thermodynamic cycle used contains: a compressor: C101, a cooler with glycolated water: E101, a condenser: El02, a liquid bottle: TK101, a filter drier: S101, an electronic expansion valve (also used for pumpdown): TCV101, two evaporator-condensers in parallel: E205:1 / 2, a liquid shock absorber bottle: TK102.

[0097] It is thus possible, without departing from the scope of the invention, to “stack” the cooling circuits (which may alternatively be four or more in number) in parallel and in cascade as described. This makes it possible to best adjust the cooling device according to the invention depending on the gas to be liquefied or the gas liquefaction installation to be equipped with such a cooling device according to the invention. The use of such a cooling device according to the invention makes it possible to separate it completely from the liquefier 7 and thus not to impose the drastic requirements and ATEX standards on all the cooling circuits of the cooling device according to the invention. In addition, this makes it possible to position the cooling device according to the invention in a location of the installation which is easy to access and which therefore simplifies the maintenance of said cooling device. On the other hand, because the cooling device according to the invention is not subject to ATEX standards, this allows the use of standard components available on the market, which greatly reduces the manufacturing cost of the cooling device according to the invention. In addition, the use of at least two compression stages greatly improves heat management for each refrigeration stage, which allows the use of less powerful compressors, and therefore reduces the manufacturing cost of the cooling device according to the invention.

[0098] On the other hand, it has been found during tests that the cooling device according to the invention makes it possible to obtain high energy yields with a COP of the order of 0.7. This allows a considerable reduction in electrical and energy consumption generally due to the fact that the cooling device according to the invention must operate 24 hours a day, 7 days a week. On the other hand, the simplicity of the cascade formed by the different cooling circuits of the cooling device according to the invention allows simple control thereof and this also facilitates the start-up and change of production flow rate as well as the configuration of the cooling device according to the invention to adapt it to the production of liquefied gases carried out by the liquefaction installation thus equipped.

[0099] Of course, it is possible to make numerous modifications to the invention without departing from its scope.

Claims

Claims

1. Cooling device (1) for a gas liquefaction installation, comprising a gas liquefier (7), the device comprising at least three independent cooling circuits (10, 20, 30) in cascade, including at least: - a low-temperature cooling circuit (30) intended to be fluidically connected to the gas liquefier; - a medium-temperature cooling circuit (20) connected to the low-temperature cooling circuit (30) via at least one first heat exchanger (E305-1, E305-2) so as to extract the calories from the low-temperature cooling circuit during operation; and - a high-temperature cooling circuit (10) connected to the medium-temperature cooling circuit (20) via at least one second heat exchanger (E205-1, E205-2) so as to extract the calories from the medium-temperature cooling circuit during operation;the high temperature cooling circuit (10) comprising at least one compressor (C101) and an associated condenser (E102), the medium (20) and low (30) temperature cooling circuits respectively comprising at least two compression stages (C201, C202, C301, C302) and an associated condenser (E205-1, E205-2, E305-1, E305-2).;

2. Cooling device according to claim 1, wherein: - the stages of the at least two compression stages of the medium temperature cooling circuit (20) are connected in series; and / or - the stages of the at least two compression stages of the low temperature cooling circuit (30) are connected in series.

3. Cooling device according to any one of claims 1 to 2, wherein: - at least one of the at least two compression stages (C201, C202) of the medium temperature cooling circuit (20) comprises at least one pre-cooler (E201, E202, E203, E204) downstream of the compressor and upstream of the associated condenser (E205-1, E205-2), preferably two pre-coolers; and / or - at least one of the at least two compression stages (C301, C302) of the low temperature cooling circuit (30) comprises at least one pre-cooler (E301, E302, E303, E304) downstream of the compressor and upstream of the associated condenser (E305-1, E305-2), preferably two pre-coolers.

4. Cooling device according to any one of claims 1 to 3, wherein: - the first heat exchanger (E305-1, E305-2) comprises at least one heat exchanger forming a condenser of the low temperature cooling circuit (30) and an evaporator of the medium temperature cooling circuit (20), preferably the first heat exchanger comprises two heat exchangers (E305-1, E305-2) connected in parallel; and / or - the second heat exchanger (E205-1, E205-2) comprises a heat exchanger (E205-1, E205-2) forming a condenser of the medium temperature cooling circuit (20) and an evaporator of the high temperature cooling circuit (10), preferably the second heat exchanger comprises two heat exchangers (E205-1, E205-2) connected in parallel.

5. Cooling device according to one of claims 1 to 5, wherein: - the low temperature cooling circuit (30) comprises a first liquid bottle (TK302) fluidly connected between the stages of the at least two compression stages; and / or - the medium temperature cooling circuit (20) comprises a second liquid bottle (TK202) fluidly connected downstream of the second heat exchanger (E205-1, E205-2) and upstream of the first heat exchanger (E305-1, E305-2); and / or - the high temperature cooling circuit (10) comprises a third liquid bottle (TK101) fluidly connected downstream of the associated condenser (E101, E102) and downstream of the second heat exchanger (E205-1, E205-2).

6. Cooling device according to claim 5, wherein: - the low temperature cooling circuit (30) comprises a first anti-knock bottle (TK303) fluidly connected downstream of the gas liquefier (7) and upstream of the at least two compressor compression stages (C301, C302); and / or - the medium temperature cooling circuit (20) comprises a second anti-knock bottle (TK203) fluidly connected downstream of the associated condenser (E305-1, E305-2) and upstream of the at least two compressor compression stages (C201, C202); and / or - the high temperature cooling circuit (10) comprises a third anti-knock bottle (TK102) fluidically connected downstream of the associated condenser (E205-1, E205-2) and upstream of the compressor (C101).

7. Cooling device according to one of claims 1 to 6, wherein: - the low temperature cooling circuit (30) comprises first oil separation means (F302, F303) downstream of the at least two compression stages; and / or - the medium temperature cooling circuit (20) comprises second oil separation means (F202, F203) downstream of the at least two compression stages; and / or - the high temperature cooling circuit comprises third oil separation means (F101) downstream of the compressor (C101).

8. Cooling device according to claim 7, wherein each of the first means (F302, F303) and / or the second means (F202, F203) and / or the third means (F101) comprises a first oil separator (F302, F202, F101), preferably each of the first means and / or the second means and / or the third means further comprises a second oil separator (F303, F203).

9. Cooling device according to one of claims 1 to 8, further comprising a group generating a cold fluid connected to at least one condenser (El02, E202, E204, E302, E304) of at least one of the low, medium and high temperature cooling circuits.

10. Device according to one of claims 1 to 9, further comprising an air heater unit connected to at least one condenser (E101, E205-1, E205-2, E305-1, E305-2) of at least one of the low, medium and high temperature cooling circuits.

11. Device according to one of claims 1 to 10, in which the low temperature cooling circuit (30) comprises a fluid characterized by: - ​​a low pressure evaporation pressure (LP) greater than atmospheric pressure; - a high pressure (HP) and low pressure (LP) ratio for each stage compression of the thermodynamic cycle which is less than 8; - the saturation temperature of the low pressure (LP) is lower than the condensation temperature of the fluid of the gas liquefier to be cooled; and - the condensation temperature is higher than the return temperature of a cold cooling fluid; preferably the fluid of the low temperature cooling circuit is methane.

12. Device according to one of claims 1 to 11, in which the medium temperature cooling circuit (20) comprises a fluid characterized by: - a low pressure (LP) evaporation pressure higher than atmospheric pressure; - a high pressure (HP) and low pressure (LP) ratio for each compression stage of the thermodynamic cycle which is less than 8; - the saturation temperature of the low pressure (LP) is lower than the condensation temperature of the fluid in the low temperature cooling circuit; and - the condensation temperature is higher than the evaporation temperature of a fluid in the high-temperature cooling circuit; preferably the medium temperature cooling circuit fluid is ethylene.

13. Device according to one of claims 1 to 12, in which the high temperature cooling circuit (10) comprises a fluid characterized by: - a low pressure (LP) evaporation pressure higher than atmospheric pressure; - a high pressure (HP) and low pressure (LP) ratio for each compression stage of the thermodynamic cycle which is less than 8; - the saturation temperature of the low pressure (LP) is lower than the condensation temperature of the fluid in the medium temperature cooling circuit; and - the condensation temperature is higher than the evaporation temperature of a fluid in the high-temperature cooling circuit; preferably the fluid of the high temperature cooling circuit is propylene.

14. Container, such as a maritime transport container, comprising the device according to one of claims 1 to 13.

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