Gas Cooling System

Abstract

This gas cooling system 100 comprises: a cooling device 120 that cools a gas to be cooled, said gas having methane as a main component; a first depressurization unit 130 that depressurizes the gas being cooled that is cooled by the cooling device 120; a nitrogen adjustment unit 150 that makes an adjustment such that the nitrogen concentration of a liquefied gas obtained due to depressurization by the first depressurization unit 130 remains within a prescribed range; a second depressurization unit 160 that depressurizes the liquefied gas of which the nitrogen concentration has been adjusted by the nitrogen adjustment unit 150; a gas-liquid separation drum (second gas-liquid separation drum 170) that conducts gas-liquid separation on the gas / liquid mixture obtained due to depressurization by the second depressurization unit 160; and a pump 180 that pressurizes the liquefied gas separated by the gas-liquid separation drum. The cooling device 120 cools the gas to be cooled using the liquefied gas pressurized by the pump 180.

Description

[Technical field]

[0001] The present disclosure relates to a gas cooling system. This application claims the benefit of priority from Japanese Patent Application No. 2021-81870, filed on May 13, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] When natural gas (NG) is transported from its place of origin, the natural gas is cooled to produce liquefied natural gas (LNG) in order to reduce the volume. As a technology for producing liquefied natural gas using a non-flammable refrigerant, a dual expander process production device that is equipped with multiple heat exchangers, multiple expanders, and multiple compressors and uses nitrogen coolant as a refrigerant has been disclosed (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 10-501053 Publication Summary of the Invention [Problem to be solved by the invention]

[0004] The technology of Patent Document 1 has a problem that the device configuration is complicated and the device itself is expensive.

[0005] In view of these problems, the present disclosure aims to provide a gas cooling system capable of producing liquefied gas with a simpler equipment configuration than conventional systems. [Means for solving the problem]

[0006] In order to solve the above problems, a gas cooling system according to one embodiment of the present disclosure includes a cooling device that cools a gas to be cooled that is mainly composed of methane, a first pressure reduction section that depressurizes the gas to be cooled by the cooling device, a nitrogen adjustment section that adjusts the nitrogen concentration of the liquefied gas obtained by depressurization by the first pressure reduction section so that it falls within a predetermined range, a second pressure reduction section that depressurizes the liquefied gas whose nitrogen concentration has been adjusted by the nitrogen adjustment section, a gas-liquid separation drum that separates the gas-liquid mixture obtained by depressurization by the second pressure reduction section into gas-liquid, and a pump that pressurizes the liquefied gas separated by the gas-liquid separation drum, and the cooling device cools the gas to be cooled with the liquefied gas pressurized by the pump.

[0007] The gas cooling system may also include a compressor that pressurizes the gas to be cooled to form a supercritical fluid, and the cooling device may include a pre-cooling section that cools the supercritical fluid and a heat exchanger that exchanges heat between the supercritical fluid and the liquefied gas pressurized by the pump, and the discharge pressure of the pump may be a pressure at which at least a portion of the liquefied gas undergoes a phase change in the heat exchanger.

[0008] The first pressure reducing section may also change the phase of the supercritical fluid into a gas-liquid mixture.

[0009] The nitrogen adjustment section may remove nitrogen from the gas-liquid mixture obtained by the pressure reduction by the first pressure reduction section, and adjust the nitrogen concentration of the liquefied gas to fall within a predetermined range.

[0010] The nitrogen adjustment section may recover methane from the separated gas constituting the gas-liquid mixture obtained by the pressure reduction by the first pressure reduction section.

[0011] The pre-cooling section may cool the supercritical fluid with a non-flammable refrigerant.

[0012] In order to solve the above problems, another gas cooling system according to an embodiment of the present disclosure includes a compressor that pressurizes a gas to be cooled, the gas being mainly composed of methane, to form a supercritical fluid, a pre-cooling section that cools the supercritical fluid, a heat exchanger that exchanges heat between the supercritical fluid and a refrigerant, a first pressure reduction section that depressurizes the supercritical fluid cooled by the heat exchanger, a second pressure reduction section that depressurizes a liquefied gas obtained by the pressure reduction by the first pressure reduction section, a gas-liquid separation drum that separates the gas-liquid mixture obtained by the pressure reduction by the second pressure reduction section into gas and liquid, and a pump that pressurizes the liquefied gas separated by the gas-liquid separation drum, wherein the heat exchanger cools the supercritical fluid using the liquefied gas pressurized by the pump as a refrigerant, and the discharge pressure of the pump is a pressure at which at least a portion of the liquefied gas undergoes a phase change in the heat exchanger. Effect of the Invention

[0013] According to the present disclosure, it is possible to produce liquefied gas using equipment with a simpler configuration than conventionally. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating a gas cooling system according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a nitrogen adjusting section according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values ​​shown in the embodiments are merely examples for ease of understanding, and do not limit the present disclosure unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are given the same reference numerals to avoid repeated explanations, and elements not directly related to the present disclosure are not illustrated.

[0016] [Gas Cooling System 100] FIG. 1 is a diagram illustrating a gas cooling system 100 according to this embodiment. In FIG. 1, solid arrows indicate the flow of a fluid. The gas cooling system 100 cools a gas to be cooled that is mainly composed of methane (CH4). In this embodiment, natural gas NG collected from a gas field is taken as an example of the gas to be cooled. The natural gas NG contains at least methane and nitrogen (N2). The gas cooling system 100 according to this embodiment is a system that uses a non-flammable refrigerant.

[0017] As shown in FIG. 1, the gas cooling system 100 includes a booster compressor 110, a heat removal section 112, a cooling device 120, a first pressure reduction section 130, a first gas-liquid separation drum 140, a nitrogen adjustment section 150, a second pressure reduction section 160, a second gas-liquid separation drum 170, a pump 180, and a flash gas compressor 190.

[0018] The booster compressor 110 (compressor) boosts the pressure of the natural gas NG and the circulating natural gas CG (for example, 30° C. and 1.5 MPaG) described later. In the process of boosting the pressure by the booster compressor 110, the natural gas NG and the circulating natural gas CG become a supercritical fluid SF. The discharge pressure of the booster compressor 110 is, for example, 7.0 MPaG.

[0019] The heat removal section 112 removes heat (cools) the supercritical fluid SF that has been heated to a high temperature by being pressurized by the booster compressor 110. The heat removal section 112 is, for example, an air-cooling device or a water-cooling device. The supercritical fluid SF whose heat has been removed by the heat removal section 112 has a temperature of, for example, 35° C. and 7.0 MPaG.

[0020] The cooling device 120 cools the supercritical fluid SF. The cooling device 120 includes a pre-cooling section 122 and a heat exchanger 124. In this embodiment, the pre-cooling section 122 cools the supercritical fluid SF with a non-flammable refrigerant (for example, carbon dioxide).

[0021] The heat exchanger 124 exchanges heat between the supercritical fluid SF and liquefied natural gas LNG (liquefied gas) pressurized by a pump 180 described later. The heat exchanger 124 includes a cooled flow path 124a and a cooling flow path 124b. The cooled flow path 124a is a flow path through which the supercritical fluid SF passes. The cooling flow path 124b is a flow path through which the liquefied natural gas LNG pressurized by the pump 180 described later passes. In the heat exchanger 124, the supercritical fluid SF and the liquefied natural gas LNG have a counterflow relationship.

[0022] The heat exchanger 124 further cools the supercritical fluid SF. The supercritical fluid SF at the outlet of the heat exchanger 124 is, for example, at −140° C. and 6.9 MPaG.

[0023] The first pressure reducing section 130 reduces the pressure of the supercritical fluid SF (natural gas NG) cooled by the heat exchanger 124 (cooling device 120). In this embodiment, the first pressure reducing section 130 is a hydraulic turbine (power recovery turbine). The first pressure reducing section 130 changes the phase of the supercritical fluid SF to a gas-liquid mixture MY. For example, the first pressure reducing section 130 reduces the pressure of the supercritical fluid SF at -140°C and 6.9 MPaG to change the phase of the supercritical fluid SF to a gas-liquid mixture MY of 0.2 MPaG or more and 0.3 MPaG or less (for example, 0.25 MPaG).

[0024] Moreover, the first pressure reduction section 130 recovers power by reducing the pressure of the supercritical fluid SF. The first pressure reduction section 130 recovers power (energy), so that the amount of evaporation during pressure reduction at the outlet of the first pressure reduction section 130 can be reduced. The power recovered by the first pressure reduction section 130 is used as power for the booster compressor 110.

[0025] The first gas-liquid separation drum 140 separates the gas-liquid mixture MY into gas and liquid. The separated gas NR separated in the first gas-liquid separation drum 140 is guided to the nitrogen adjustment section 150. As described above, the natural gas NG contains methane and nitrogen. The boiling point of nitrogen is lower than that of methane. Therefore, the nitrogen concentration of the separated gas NR gas (nitrogen-enriched gas) is higher than that of the natural gas NG. For example, the nitrogen concentration of the separated gas NR gas is 10% by volume.

[0026] The nitrogen adjustment section 150 adjusts the nitrogen concentration of the liquefied gas LA obtained by the pressure reduction by the first pressure reduction section 130 so as to fall within a predetermined range. In this embodiment, the nitrogen adjustment section 150 removes nitrogen from the gas-liquid mixture MY to adjust the nitrogen concentration of the liquefied gas LA stored in the first gas-liquid separation drum 140. In this embodiment, the nitrogen adjustment section 150 removes nitrogen from the separated gas NR.

[0027] Fig. 2 is a diagram illustrating the nitrogen adjustment unit 150 according to this embodiment. In Fig. 2, solid arrows indicate the flows of the gas-liquid mixture MY, the liquefied gas LA, and the liquefied gas ML. In Fig. 2, dashed arrows indicate the flows of the separated gas NR and the exhaust gas EX.

[0028] As shown in FIG. 2, the nitrogen adjustment section 150 includes a compressor 152 and a methane recovery section 154.

[0029] The compressor 152 pressurizes the post-separation gas NR and guides it to the methane recovery section 154. The compressor 152 pressurizes the post-separation gas NR (for example, 0.25 MPaG) to, for example, 0.6 MPaG.

[0030] The separated gas NR and liquefied natural gas LNG (for example, -155°C, 0.6 MPaG) are guided to the methane recovery section 154. The methane recovery section 154 recovers methane from the separated gas NR. The methane recovery section 154 absorbs the methane contained in the separated gas NR into the liquefied natural gas LNG by contacting (cleaning) the liquefied natural gas LNG with the separated gas NR. The methane-enriched liquefied gas LM (liquefied natural gas LNG that has absorbed methane) generated in the methane recovery section 154 is guided to a second gas-liquid separation drum 170 described later. The methane-enriched liquefied gas LM has, for example, a temperature of -135°C and 0.6 MPaG.

[0031] On the other hand, the separated gas NR from which methane has been removed in the methane recovery section 154 is exhausted to the outside as exhaust gas EX. The exhaust gas EX is used, for example, as fuel for a plant in which the gas cooling system 100 is provided.

[0032] A central control unit (not shown) controls the flow rate of the compressor 152 so that the nitrogen concentration of the liquefied gas LA is within a predetermined range (for example, 0.5 mol% to 2 mol%). As a result, the central control unit controls the pressure of the first gas-liquid separation drum 140, and also controls the flow rate of the liquefied natural gas LNG guided to the methane recovery unit 154.

[0033] The central control unit is composed of a semiconductor integrated circuit including a CPU (Central Processing Unit). The central control unit reads out programs and parameters for operating the CPU itself from the ROM. The central control unit manages and controls the entire gas cooling system 100 in cooperation with the RAM as a work area and other electronic circuits.

[0034] Returning to Fig. 1, the second pressure reducing section 160 reduces the pressure of the liquefied gas LA whose nitrogen concentration has been adjusted by the nitrogen adjusting section 150. In this embodiment, the second pressure reducing section 160 is a pressure reducing valve. The second pressure reducing section 160 reduces the pressure (flashes (evaporative cooling)) of the liquefied gas LA to produce a gas-liquid mixture MZ of, for example, -155°C and 0.05 MPaG.

[0035] The second gas-liquid separation drum 170 (gas-liquid separation drum) separates the gas-liquid mixture MZ into gas and liquid.

[0036] The pump 180 pressurizes the liquefied natural gas LNG (liquefied gas) separated from the gas-liquid mixture MZ by the second gas-liquid separation drum 170. In this embodiment, the discharge pressure of the pump 180 is a pressure at which at least a part of the liquefied natural gas LNG (liquefied gas) undergoes a phase change (vaporization) in the heat exchanger 124. The discharge pressure of the pump 180 is in a range from a predetermined lower limit pressure to a predetermined upper limit pressure. The lower limit pressure is, for example, 1.0 MPaG. The upper limit pressure is, for example, 2.0 MPaG. For example, the pump 180 pressurizes the liquefied natural gas LNG to 1.6 MPaG. The pump 180 pressurizes the liquefied natural gas LNG to shift the temperature at which it vaporizes during heat exchange in the heat exchanger 124. The discharge pressure of the pump 180 can be measured by a mechanical pressure gauge or a pressure gauge including a pressure receiving element.

[0037] The pressurized liquefied natural gas LNG is shipped as a product or supplied to an LNG user. A part of the pressurized liquefied natural gas LNG is guided to the heat exchanger 124 of the cooling device 120, and then guided to the pre-cooling section 122, where it is recovered as cold heat as part of the refrigerant that cools the natural gas NG in the cooling device 120.

[0038] The flash gas compressor 190 pressurizes the flash gas FG separated in the second gas-liquid separation drum 170. For example, the flash gas compressor 190 pressurizes the flash gas FG to 1.5 MPaG. The flash gas FG pressurized by the flash gas compressor 190 is guided to the pre-cooling section 122, where cold heat is recovered as part of the refrigerant.

[0039] As described above, the gas cooling system 100 according to this embodiment uses the produced liquefied natural gas LNG as a refrigerant for cooling the natural gas NG. As a result, the gas cooling system 100 can omit some of the compressors and coolers dedicated to the refrigerant, compared to the dual expander process of the conventional technology. Therefore, the gas cooling system 100 can simplify the equipment configuration, and can reduce the cost required for liquefaction.

[0040] Moreover, the pre-cooling unit 122 of the gas cooling system 100 cools the supercritical fluid SF with a non-flammable refrigerant. Therefore, the gas cooling system 100 can inexpensively produce liquefied natural gas LNG by using the pre-cooling unit 122 that uses a non-flammable refrigerant in combination.

[0041] As described above, natural gas NG contains a small amount of nitrogen in addition to methane. Since the boiling point of nitrogen is lower than that of methane, the flash gas FG generated by the pressure reduction by the second pressure reduction unit 160 contains nitrogen in preference to methane. For this reason, if the nitrogen adjustment unit 150 is not provided, when the flash gas FG is returned to the booster compressor 110, the nitrogen concentration of the natural gas NG as the gas to be cooled increases (nitrogen is concentrated in the natural gas NG) as the operation time of the gas cooling system 100 elapses, and the amount of the flash gas FG increases. In addition, if the nitrogen concentration of the natural gas NG increases too much, the liquefaction efficiency decreases. For this reason, if the nitrogen adjustment unit 150 is not provided, the flash gas FG must be discarded, which causes a problem that the methane contained in the flash gas FG is also discarded.

[0042] Therefore, as described above, the gas cooling system 100 includes the nitrogen adjusting section 150 that removes nitrogen from the gas-liquid mixture MY. This allows the gas cooling system 100 to prevent an increase in the flash gas FG and maintain the flash gas FG at a predetermined target amount. The target amount is an amount of flash gas FG that, when the flash gas FG is returned to the booster compressor 110, makes the nitrogen concentration of the natural gas NG after being pressurized by the booster compressor 110 a nitrogen concentration at which the natural gas NG is efficiently liquefied. Therefore, even if the flash gas FG is returned to the booster compressor 110 (pre-cooling section 122), the gas cooling system 100 can maintain the nitrogen concentration of the natural gas NG at a concentration at which the natural gas NG can be efficiently liquefied. Therefore, the gas cooling system 100 can avoid a situation in which methane contained in the flash gas FG is unnecessarily discarded. In addition, since the flash gas FG can be maintained at the target amount, the gas cooling system 100 can prevent an increase in the power of the flash gas compressor 190.

[0043] If the nitrogen concentration of the liquefied gas LA is less than the lower limit of the above-mentioned predetermined range (e.g., 0.5 mol%), the cooling efficiency of the second pressure reduction section 160 decreases. On the other hand, if the nitrogen concentration of the liquefied gas LA exceeds the upper limit of the above-mentioned predetermined range (e.g., 2 mol%), the flash gas FG exceeds the target amount.

[0044] Therefore, as described above, the nitrogen adjustment unit 150 sets the nitrogen concentration of the liquefied gas LA guided to the second pressure reduction unit 160 to be equal to or higher than the lower limit. This allows the gas cooling system 100 to improve the cooling efficiency by the second pressure reduction unit 160. Therefore, it is possible to lower the temperature of the liquefied natural gas LNG generated by the pressure reduction by the second pressure reduction unit 160. In other words, the gas cooling system 100 can lower the temperature of the liquefied natural gas LNG guided to the heat exchanger 124 by the pump 180, and it is possible to efficiently cool the supercritical fluid SF by the heat exchanger 124.

[0045] As described above, the nitrogen adjustment section 150 adjusts the nitrogen concentration of the liquefied gas LA guided to the second pressure reduction section 160 to be equal to or lower than the upper limit value. This enables the gas cooling system 100 to maintain the flash gas FG generated in the second gas-liquid separation drum 170 at a target amount.

[0046] As described above, the heat exchanger 124 cools the supercritical fluid SF with the liquefied natural gas LNG. In the heat exchanger 124, it is desirable to make the flow rate of the liquefied natural gas LNG as small as possible compared to the flow rate of the supercritical fluid SF. Therefore, the heat exchanger 124 uses the latent heat due to the phase change of the liquefied natural gas LNG to cool the supercritical fluid SF with a smaller flow rate of the liquefied natural gas LNG. In order to reduce the flow rate of the liquefied natural gas LNG, it is necessary to lower the pressure of the liquefied natural gas LNG introduced to the heat exchanger 124 to lower the phase change temperature. On the other hand, if the pressure of the liquefied natural gas LNG introduced to the heat exchanger 124 becomes too low, the pressure of the circulating natural gas CG introduced to the booster compressor 110 will become low, and the power of the booster compressor 110 will become large. Furthermore, if the pressure of the liquefied natural gas LNG introduced into the heat exchanger 124 becomes too high, the phase change temperature becomes high and the liquefied natural gas LNG will no longer undergo a phase change in the heat exchanger 124.

[0047] Therefore, it is necessary to appropriately set the phase change temperature of the liquefied natural gas LNG guided to the heat exchanger 124. For this reason, the discharge pressure of the pump 180 that pressurizes the liquefied natural gas LNG guided to the heat exchanger 124 is set in a range from a predetermined lower limit pressure to a predetermined upper limit pressure. The lower limit pressure is a pressure at which the power of the booster compressor 110 does not increase excessively. This makes it possible for the pump 180 to prevent an excessive increase in the power of the booster compressor 110.

[0048] Furthermore, the upper limit pressure is a pressure at which at least a portion of the liquefied natural gas LNG undergoes a phase change in the heat exchanger 124. This allows the heat exchanger 124 to cool the supercritical fluid SF with the latent heat of the liquefied natural gas LNG. Therefore, the heat exchanger 124 can cool the supercritical fluid SF with a smaller amount of liquefied natural gas LNG than the supercritical fluid SF.

[0049] As described above, the first pressure reducing section 130 changes the phase of the supercritical fluid SF to the gas-liquid mixture MY. Therefore, the first pressure reducing section 130 can efficiently cool the supercritical fluid SF. The first pressure reducing section 130 can also transfer nitrogen to the separated gas NR. This allows the nitrogen adjusting section 150 to efficiently remove nitrogen.

[0050] As described above, the nitrogen adjustment unit 150 includes the methane recovery unit 154. This allows the methane recovery unit 154 to increase the methane concentration in the liquefied natural gas LNG (liquefied gas LA).

[0051] [Variations] In the above embodiment, the gas cooling system 100 cools natural gas NG extracted from a gas field, that is, gas containing nitrogen in addition to methane. Therefore, the nitrogen adjustment unit 150 adjusts the nitrogen concentration of the liquefied gas LA guided to the second pressure reduction unit 160 by removing nitrogen from the gas-liquid mixture MY.

[0052] However, when the gas cooling system 100 cools a gas to be cooled that contains almost no nitrogen, such as renewable natural gas (RNG) or synthetic natural gas (SNG), the nitrogen adjustment unit 150 adds nitrogen to the liquefied gas LA to optimize the nitrogen concentration of the liquefied gas LA.

[0053] In this case, the nitrogen adjustment section 150 adds nitrogen to the natural gas NG at the inlet of the booster compressor 110, so that the nitrogen concentration of the liquefied gas LA guided to the second pressure reducing section 160 is equal to or higher than the lower limit and equal to or lower than the upper limit.

[0054] As a result, the gas cooling system 100 according to the modified example can improve the cooling efficiency by the second decompression section 160.

[0055] Although the embodiments have been described above with reference to the accompanying drawings, it goes without saying that the present disclosure is not limited to the above-described embodiments. It is clear that a person skilled in the art can think of various modified or altered examples within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present disclosure.

[0056] For example, in the above embodiment, the nitrogen adjustment unit 150 is provided with the methane recovery unit 154. However, the nitrogen adjustment unit 150 does not have to be provided with the methane recovery unit 154. It is sufficient that the nitrogen adjustment unit 150 is at least capable of adjusting the nitrogen concentration of the liquefied gas LA obtained by depressurizing the liquefied gas LA by the first depressurization unit 130.

[0057] In the above embodiment, the central control unit controls the pressure of the first gas-liquid separation drum 140 and the flow rate of the liquefied natural gas LNG guided to the methane recovery unit 154 by controlling the flow rate of the compressor 152 so that the nitrogen concentration of the liquefied gas LA is within a predetermined range. However, when the nitrogen concentration of the natural gas NG is approximately constant, the central control unit does not need to control the flow rate of the compressor 152 (does not control the pressure of the first gas-liquid separation drum 140) and does not need to control the flow rate of the liquefied natural gas LNG guided to the methane recovery unit 154. In this case, the flow rate of the compressor 152 and the flow rate of the liquefied natural gas LNG guided to the methane recovery unit 154 are designed so that the nitrogen concentration of the liquefied gas LA is 0.5 mol% or more and 2 mol% or less.

[0058] In the above embodiment and modified examples, the gas cooling system 100 is exemplified as including the nitrogen adjustment unit 150. However, the gas cooling system 100 does not have to include the nitrogen adjustment unit 150. That is, the gas cooling system includes a booster compressor 110 that pressurizes a gas to be cooled, which is mainly composed of methane, to turn it into a supercritical fluid SF, a pre-cooling section 122 that cools the supercritical fluid SF, a heat exchanger 124 that exchanges heat between the supercritical fluid SF and a refrigerant, a first pressure reduction section 130 that depressurizes the supercritical fluid SF cooled by the heat exchanger 124, a second pressure reduction section 160 that depressurizes the liquefied gas obtained by the pressure reduction by the first pressure reduction section 130, a gas-liquid separation drum (second gas-liquid separation drum 170) that separates the gas-liquid mixture obtained by the pressure reduction by the second pressure reduction section 160 into gas and liquid, and a pump 180 that pressurizes the liquefied gas separated by the gas-liquid separation drum, and the heat exchanger 124 cools the supercritical fluid SF using the liquefied gas pressurized by the pump 180 as a refrigerant, and the discharge pressure of the pump is a pressure at which at least a portion of the liquefied gas changes phase in the heat exchanger 124.

[0059] The pump 180 of the gas cooling system sets the discharge pressure to be equal to or higher than the lower limit pressure and equal to or lower than the upper limit pressure. As described above, the lower limit pressure is a pressure at which the power of the booster compressor 110 does not increase excessively. This enables the pump 180 to prevent an excessive increase in the power of the booster compressor 110.

[0060] Similarly, the upper limit pressure is the pressure at which at least a portion of the liquefied natural gas LNG undergoes a phase change in the heat exchanger 124. This allows the heat exchanger 124 to cool the supercritical fluid SF with the latent heat of the liquefied natural gas LNG. Therefore, the heat exchanger 124 can cool the supercritical fluid SF with a smaller amount of liquefied natural gas LNG than the supercritical fluid SF.

[0061] This disclosure enables efficient liquefaction of renewable natural gas with low supply pressure, which can contribute, for example, to Sustainable Development Goals (SDGs) Goal 7 "Ensure access to affordable, reliable, sustainable and modern energy" and Goal 13 "Take urgent action to combat climate change and its impacts." [Explanation of symbols]

[0062] 100: Gas cooling system 110: Booster compressor (compressor) 120: Cooling device 122: Pre-cooling section 124: Heat exchanger 130: First pressure reduction section 150: Nitrogen adjustment section 160: Second pressure reduction section 170: Second gas-liquid separation drum (gas-liquid separation drum) 180: Pump

Claims

1. A cooling device that cools a gas to be cooled that contains methane as a main component; a first pressure reducing unit that reduces the pressure of the gas to be cooled that has been cooled by the cooling device; a nitrogen adjusting unit that adjusts the nitrogen concentration of the liquefied gas obtained by the pressure reduction by the first pressure reducing unit so that the nitrogen concentration falls within a predetermined range; A second pressure reducing unit that reduces the pressure of the liquefied gas whose nitrogen concentration has been adjusted by the nitrogen adjusting unit; a gas-liquid separation drum that separates the gas-liquid mixture obtained by the pressure reduction by the second pressure reduction section into gas and liquid; a pump for pressurizing the liquefied gas separated by the gas-liquid separation drum; Equipped with The cooling device is a gas cooling system that cools the gas to be cooled with liquefied gas pressurized by the pump.

2. a compressor for pressurizing the gas to be cooled into a supercritical fluid, The cooling device includes: A pre-cooling unit that cools the supercritical fluid; a heat exchanger for exchanging heat between the supercritical fluid and the liquefied gas pressurized by the pump; having The gas cooling system of claim 1 , wherein the discharge pressure of the pump is a pressure at which at least a portion of the liquefied gas undergoes a phase change in the heat exchanger.

3. The gas cooling system of claim 2 , wherein the first pressure reducing section changes the phase of the supercritical fluid to a gas-liquid mixture.

4. The gas cooling system according to claim 3, wherein the nitrogen adjustment unit removes nitrogen from the gas-liquid mixture obtained by the pressure reduction by the first pressure reduction unit, and adjusts the nitrogen concentration of the liquefied gas to fall within a predetermined range.

5. The gas cooling system according to claim 4 , wherein the nitrogen adjustment unit recovers methane from a separated gas that constitutes the gas-liquid mixture obtained by the pressure reduction by the first pressure reduction unit.

6. The gas cooling system according to claim 2 , wherein the pre-cooling unit cools the supercritical fluid with a non-flammable refrigerant.

7. A compressor for pressurizing a gas to be cooled, the gas being mainly composed of methane, to a supercritical fluid; A pre-cooling unit that cools the supercritical fluid; a heat exchanger for exchanging heat between the supercritical fluid and a refrigerant; a first pressure reducing unit that reduces the pressure of the supercritical fluid cooled by the heat exchanger; A second pressure reducing unit that reduces the pressure of the liquefied gas obtained by the pressure reduction by the first pressure reducing unit; a gas-liquid separation drum that separates the gas-liquid mixture obtained by the pressure reduction by the second pressure reduction section into gas and liquid; a pump for pressurizing the liquefied gas separated by the gas-liquid separation drum; Equipped with The heat exchanger cools the supercritical fluid using the liquefied gas pressurized by the pump as a refrigerant, A gas cooling system, wherein the discharge pressure of the pump is a pressure at which at least a portion of the liquefied gas changes phase in the heat exchanger.

Images