LNG (Liquefied Natural Gas) cold energy air liquefaction system based on vapor compression type heat pump circulation

Abstract

The invention relates to the technical field of air liquefaction, in particular to an LNG (Liquefied Natural Gas) cold energy air liquefaction system based on vapor compression type heat pump circulation, which comprises an LNG gasification circulation unit and a vapor compression type cold energy transmission heat pump circulation unit, a circulation refrigerant circulates in the LNG gasification circulation unit and is used for recovering LNG liquid low-temperature cold energy to liquefy lower-temperature air; an air pressurization liquefaction circulation unit; and the secondary refrigerant gas cooling circulation unit is used for recovering sensible heat cold energy of gasified LNG and cooling gas compressed by the steam compression type cold energy transmission heat pump circulation unit and the air pressurization liquefaction circulation unit. According to the LNG cold energy air liquefaction system based on the vapor compression type heat pump cycle, LNG liquid low-temperature cold energy is recycled, the temperature grade of the cold energy is improved, then lower-temperature air is liquefied, phase-change throttling heat exchange is adopted in the vapor compression cycle, cooling is fast, the variable load capacity is high, and the energy consumption is low. And the LNG cold energy is efficiently recycled to continuously liquefy air under the LNG discontinuous supply fluctuation working condition.

Description

Technical Field

[0001] The invention relates to the technical field of air liquefaction, and in particular to an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle. Background Art

[0002] LNG is an ultra-low temperature liquid natural gas that needs to maintain an extremely low temperature (about -162°C) during storage and transportation. In this low temperature state, LNG releases a large amount of high-grade cold energy during the regasification process before being supplied to users. After years of practice, LNG cold energy utilization includes cold energy power generation, air separation, light hydrocarbon recovery, low temperature crushing, seawater desalination, freezing and refrigeration, dry ice manufacturing, etc. The existing LNG cold energy utilization technology alone cannot efficiently utilize the cold energy of LNG in the entire temperature range, and the cold energy loss is large. With the rapid growth of LNG consumption and the intensification of the global energy supply tension, it is particularly important to efficiently utilize LNG cold energy.

[0003] Air liquefaction is a process that converts air from gas to liquid by lowering its temperature to below its liquefaction point. It is widely used in industrial gas production, healthcare, food processing, oxygen-enriched combustion and carbon capture, energy storage, and hydrogen liquefaction precooling.

[0004] In the prior art, there are air liquefaction systems that utilize LNG gasification, including air expansion refrigeration systems that use direct heat exchange between LNG and air, but there are safety risks of flammable and explosive hydrocarbons coming into contact with air; and air liquefaction systems that use pressurized nitrogen as the intermediate transmission medium for LNG cold energy, according to the physical properties of methane, LNG is gasified at normal pressure, and its boiling point is -162°C. The pressure of nitrogen corresponding to this temperature is 1.6MPa, that is, only when nitrogen is compressed to above 1.6MPa can LNG cold energy be directly utilized. The nitrogen cycle pressure is high and the energy consumption is high. In order to reduce the energy consumption of the system using nitrogen cycle, expensive cryogenic nitrogen compressors are usually used, so the system economy and the reliability of cryogenic compressors are poor. At the same time, the presence of complex heavy hydrocarbon components in LNG causes the LNG phase change temperature to change with the gasification process. At the same time, as the gas consumption of LNG changes, its gasification volume fluctuates greatly and is highly discontinuous. Therefore, the existing LNG cold energy air liquefaction system has problems such as high operating pressure, slow cooling speed, low efficiency, poor economy of expensive cryogenic compressors, inability to adapt to the discontinuous gasification of LNG, and weak air liquefaction load adjustment capability.

[0005] Therefore, how to provide a more suitable LNG composition and discontinuous gasification cold energy recovery air liquefaction cycle is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0006] The present invention provides an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle, which is used to solve the defect that the LNG condensation air liquefaction system in the prior art cannot adapt to the discontinuous supply of LNG, and realizes the recovery of low-temperature cold energy of LNG liquid and improves the temperature grade of cold energy to liquefy lower-temperature air. The vapor compression cycle adopts throttling phase change heat transfer, has fast cooling and strong variable load capacity, and is suitable for efficiently recovering LNG cold energy for continuous liquefaction of air under the condition of discontinuous LNG supply and fluctuation.

[0007] The present invention provides an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle, comprising: The LNG gasification circulation unit comprises a first heat exchanger, a second heat exchanger and an LNG pressure regulating device; the first heat exchanger is connected to the LNG storage tank; the LNG pressure regulating device is used to increase the pressure of the LNG; A vapor compression cold energy transfer heat pump circulation unit, in which a circulating refrigerant flows, is used to recover the low-temperature cold energy of LNG liquid to liquefy lower-temperature air; The air pressurization liquefaction circulation unit comprises an air compressor, an air cooler and a third heat exchanger which are connected in sequence; and the third heat exchanger is used for heat exchange between air and circulating refrigerant; The refrigerant gas cooling circulation unit is used for recovering the sensible heat and cold energy of the gasified LNG and cooling the gas compressed by the vapor compression cold energy transmission heat pump circulation unit and the air pressurization liquefaction circulation unit.

[0008] According to the present invention, a LNG cold energy air liquefaction system based on a vapor compression heat pump cycle is provided, wherein the vapor compression cold energy transmission heat pump cycle unit is a cascade type, including a methane heat pump cycle loop and an argon heat pump cycle loop, and the circulating refrigerants are methane and argon respectively; The methane heat pump circulation loop includes a loop formed by a first compressor, a first gas cooler, the first heat exchanger, a first gas throttle and a fourth heat exchanger; methane is cooled by the first gas cooler and the brine gas cooling circulation unit; The argon heat pump circulation loop includes a loop formed by a second compressor, a second gas cooler, the fourth heat exchanger, a second gas throttle and the third heat exchanger; the argon gas is cooled by the second gas cooler and the refrigerant gas cooling circulation unit.

[0009] According to the present invention, an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle is provided, wherein the refrigerant gas cooling circulation unit includes a loop formed by a refrigerant circulation pump, the second heat exchanger, a refrigerant splitter and a refrigerant manifold, and the air cooler, the first gas cooler and the second gas cooler are arranged in parallel between the refrigerant splitter and the refrigerant manifold.

[0010] According to an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle provided by the present invention, the LNG pressure regulating device includes an LNG throttling device and a natural gas compressor, the LNG throttling device is arranged upstream of the first heat exchanger, and the natural gas compressor is arranged downstream of the second heat exchanger.

[0011] According to an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle provided by the present invention, the LNG pressure regulating device includes a cryogenic pump and a natural gas compressor, the cryogenic pump is arranged upstream of the first heat exchanger, and the natural gas compressor is arranged downstream of the second heat exchanger.

[0012] According to an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle provided by the present invention, the LNG pressure regulating device includes an LNG throttling device, a cryogenic pump and an ejector, the LNG throttling device and the cryogenic plate are connected in parallel and are both arranged upstream of the first heat exchanger, and the ejector is arranged downstream of the second heat exchanger.

[0013] According to the LNG cold energy air liquefaction system based on a vapor compression heat pump cycle provided by the present invention, the refrigerant is a solution that remains in a liquid state during the cycle.

[0014] According to an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle provided by the present invention, the LNG gasification cycle unit also includes a natural gas cooling device, which is arranged downstream of the natural gas compressor, and the outlet of the natural gas cooling device is connected to the city gas pipeline network.

[0015] According to an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle provided by the present invention, the air compressor is a multi-stage compression unit, and an air cooler is provided downstream of each compression unit.

[0016] According to an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle provided by the present invention, the air pressurization liquefaction cycle unit further includes an air drying purifier disposed between the air cooler and the third heat exchanger.

[0017] The LNG cold energy air liquefaction system based on the vapor compression heat pump cycle provided by the present invention recovers the low-temperature cold energy of LNG liquid through the vapor compression cold energy transmission heat pump circulation unit to liquefy air with lower temperature; recovers the sensible heat cold energy of the vaporized LNG through the refrigerant gas cooling circulation unit, and cools the gas compressed by the vapor compression cold energy transmission heat pump circulation unit and the air pressurization liquefaction circulation unit; the present invention uses the heat pump technology to transfer the condensation heat of air with lower liquefaction temperature to the LNG vaporization temperature zone with higher temperature through the vapor compression circulation pump, that is, to recover the low-temperature cold energy of LNG liquid and improve the temperature grade of the cold energy to liquefy air with lower temperature. The vapor compression cycle adopts throttling phase change heat transfer, has fast cooling and strong variable load capacity, and is suitable for efficiently recovering LNG cold energy for continuous liquefaction of air under the condition of discontinuous supply and fluctuation of LNG.

[0018] The vapor compression cold energy transmission heat pump circulation unit uses methane and argon as the two-stage cascade heat pump circulation refrigeration medium, which can effectively match the change in phase change temperature of LNG during the gasification process caused by the complex heavy hydrocarbon components of LNG. At the same time, in the air liquefaction process, the inert gas argon is used as the heat pump circulation medium for heat exchange with air, which can avoid direct heat exchange between hydrocarbons in LNG and air, effectively avoid the accumulation of hydrocarbons in liquefied air, and prevent safety problems caused by natural gas leakage into the air liquefaction system, thereby improving system safety.

[0019] The latent heat of argon is higher than that of nitrogen, the amount of argon circulation is small, and the energy consumption is low. Each circulation unit of the system uses a normal temperature compressor, which can achieve better energy-saving effects than the nitrogen circulation using a low-temperature compressor in the existing LNG cold energy air liquefaction system. It achieves energy saving in the air liquefaction system while improving the economy and reliability of the system.

[0020] The critical temperature and boiling point of argon at the same pressure are higher than those of nitrogen, and between nitrogen and methane. Using argon as the circulating medium during the air liquefaction process reduces the system pressure and the requirements for the pressure resistance of the equipment, which can effectively achieve energy saving.

[0021] Through the heat exchange between the refrigerant and the gasified LNG, it is used for gas cooling in each circulation unit of the system, so as to further utilize the sensible heat of LNG and reduce the energy consumption of the compressor in the system, thereby realizing the efficient utilization of the cold energy of LNG latent heat and sensible heat in the entire temperature range in the single technical application scenario of air liquefaction separation. Compared with the conventional pure electric refrigeration liquid air production system and the existing LNG cold energy air liquefaction system, it has huge energy-saving benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is one of the structural principle diagrams of the LNG cold energy air liquefaction system based on the vapor compression heat pump cycle provided by the present invention.

[0024] Figure 2 This is the second structural principle diagram of the LNG cold energy air liquefaction system based on the vapor compression heat pump cycle provided by the present invention.

[0025] Figure 3 This is the third structural principle diagram of the LNG cold energy air liquefaction system based on the vapor compression heat pump cycle provided by the present invention.

[0026] Figure 4 This is the fourth structural principle diagram of the LNG cold energy air liquefaction system based on the vapor compression heat pump cycle provided by the present invention.

[0027] Figure 5 This is the fifth structural principle diagram of the LNG cold energy air liquefaction system based on the vapor compression heat pump cycle provided by the present invention.

[0028] Reference numerals: 1. LNG gasification circulation unit; 2. Vapor compression cold energy transmission heat pump circulation unit; 3. Air pressurization liquefaction circulation unit; 4. Refrigerant gas cooling circulation unit; 11. First heat exchanger; 12. Second heat exchanger; 13. LNG throttling device; 14. Natural gas compressor; 15. Cryogenic pump; 16. Ejector; 17. Natural gas cooling device; 21. Methane heat pump circulation loop; 22. Argon heat pump circulation loop; 211. First compressor; 212. First gas cooler; 213. First gas throttle; 214. Fourth heat exchanger; 221. Second compressor; 222. Second gas cooler; 223. Second gas throttle; 31. Air compressor; 32. Air cooler; 33. Third heat exchanger; 34. Air drying purifier; 41. Refrigerant circulation pump; 42. Refrigerant splitter; 43. Refrigerant concentrator. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limitations on the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0031] Combine the following Figure 1-Figure 5 The present invention describes an LNG cold energy air liquefaction system based on a vapor compression heat pump cycle.

[0032] Figure 1 The invention provides one of the LNG cold energy air liquefaction systems based on the vapor compression heat pump cycle, such as Figure 1 As shown, it includes an LNG gasification circulation unit 1, a vapor compression cold energy transmission heat pump circulation unit 2, an air pressurized liquefaction circulation unit 3 and a refrigerant gas cooling circulation unit 4.

[0033] The LNG gasification circulation unit 1 includes a first heat exchanger 11, a second heat exchanger 12, an LNG pressure regulating device and corresponding pipelines. The first heat exchanger 11 is connected to the LNG storage tank; the LNG pressure regulating device is used to increase the pressure of LNG, gasify the LNG from the LNG storage tank and lift it to the city gas pipeline network.

[0034] A circulating refrigerant circulates in the vapor compression cold energy transfer heat pump circulation unit 2, which is used to recover the low-temperature cold energy of the LNG liquid to liquefy the air at a lower temperature.

[0035] The air pressurized liquefaction circulation unit 3 comprises a series circuit consisting of an air compressor 31, an air cooler 32 and a third heat exchanger 33 connected in sequence; and the third heat exchanger 33 is used for heat exchange between air and circulating refrigerant.

[0036] The refrigerant gas cooling circulation unit 4 is used to recover the sensible heat and cold energy of the gasified LNG, and to cool the gas compressed by the vapor compression cold energy transmission heat pump circulation unit 2 and the air pressurization liquefaction circulation unit 3 .

[0037] The LNG cold energy air liquefaction system based on the vapor compression heat pump cycle provided in the embodiment of the present invention pumps the condensation heat of air liquefaction with a lower liquefaction temperature to the LNG vaporization temperature zone with a higher temperature through the vapor compression heat pump cycle, that is, the low-temperature cold energy of the LNG liquid is recovered through the vapor compression heat pump cycle and the temperature grade of the cold energy is increased to liquefy the air at a lower temperature. At the same time, the vapor compression heat pump has a wide range of adjustment of the refrigerant circulation quality, which can adapt to the fluctuating working conditions of discontinuous LNG gasification to achieve efficient utilization of LNG cold energy and stable liquefaction of air.

[0038] In one embodiment of the present invention, the vapor compression cold energy transmission heat pump circulation unit 2 can be a single-stage vapor compression heat pump circulation loop, and the single-stage vapor compression heat pump circulation loop uses argon as the refrigerant of the heat pump system. The argon heat pump circulation effectively isolates the direct heat exchange between hydrocarbons and air, reducing the safety risk of hydrocarbon substances accumulated in liquefied air. At the same time, the cold energy transmission heat pump circulation uses a normal temperature compressor to avoid the use of a low-temperature compressor, thereby improving the economy of the device.

[0039] In addition, the latent heat of argon is higher than that of nitrogen, the amount of argon circulation is small, and the energy consumption is low. Each circulation unit of the system uses a normal temperature compressor, which can achieve better energy-saving effects than the nitrogen circulation in the existing LNG cold energy air liquefaction system using a low-temperature compressor. This achieves energy saving in the air liquefaction system while improving the economy and reliability of the system.

[0040] Moreover, the critical temperature and boiling point of argon at the same pressure are higher than those of nitrogen, and between nitrogen and methane. Using argon as the circulating medium reduces the system pressure in the air liquefaction process, alleviates the requirements for the pressure resistance of the equipment, and can effectively achieve energy saving.

[0041] It should be noted that when using a single-stage vapor compression heat pump cycle, it is necessary to throttle first and then use the natural gas compressor to pressurize, such as Figure 4 and Figure 5 , first throttle and then increase the pressure, the LNG pressure energy can be converted into high-grade temperature energy, such as throttling and reducing the pressure to about 115kPa, making full use of the LNG temperature grade, and a single-stage heat pump cycle can be used to achieve air liquefaction.

[0042] In a feasible embodiment of the present invention, the vapor compression cold energy transmission heat pump circulation unit 2 can be a cascade type, including a methane heat pump circulation loop 21 and an argon heat pump circulation loop 22, forming a two-stage cascade cycle, using methane and argon as refrigerants for the heat pump system. The two-stage cascade heat pump cycle using two-stage methane and argon can effectively match the change in the phase change temperature of the complex heavy hydrocarbon components of LNG. At the same time, the argon heat pump cycle effectively isolates the direct heat exchange between hydrocarbons and air, reducing the safety risk of hydrocarbon substances accumulated in liquefied air. At the same time, the cold energy transmission heat pump cycle uses a normal temperature compressor to avoid the use of a low-temperature compressor, thereby improving the economy of the device.

[0043] Specifically, the methane heat pump circulation loop 21 includes a loop formed by a first compressor 211, a first gas cooler 212, a first heat exchanger 11, a first gas throttle 213 and a fourth heat exchanger 214; methane is cooled by the first gas cooler 212 and the refrigerant gas cooling circulation unit.

[0044] The argon heat pump circulation loop 22 includes a loop formed by a second compressor 221 , a second gas cooler 222 , a fourth heat exchanger 214 , a second gas throttle 223 and a third heat exchanger 33 ; the argon gas is cooled by the second gas cooler 222 and the refrigerant gas cooling circulation unit 4 .

[0045] In another embodiment of the present invention, a krypton heat pump circulation loop and an argon heat pump circulation loop may also be included. Using krypton / argon as the refrigerant of the heat pump system can better match the LNG gasification temperature curve, transform low-temperature compression into normal-temperature compression, and achieve high reliability.

[0046] In a feasible embodiment of the present invention, the refrigerant gas cooling circulation unit 4 includes a refrigerant circulation pump 41, a second heat exchanger 12, a refrigerant flow divider 42 and a refrigerant flow converging unit 43 to form a loop, and an air cooler 32, a first gas cooler 212 and a second gas cooler 222 are arranged in parallel between the refrigerant flow divider 42 and the refrigerant flow converging unit 43. The refrigerant is a liquid solution at a temperature above -100°C under normal pressure, such as ethylene glycol solution, propylene glycol solution, glycerol solution, salt solution, etc.

[0047] In the above embodiments, ethylene glycol aqueous solution is used for heat exchange with gasified LNG for gas cooling in each circulation unit of the system, thereby further utilizing the sensible heat of LNG and reducing the energy consumption of the compressor in the system, thereby realizing efficient utilization of the cold energy of LNG latent heat and sensible heat in the entire temperature range in a single technical application scenario of air liquefaction separation, which has huge energy-saving benefits compared with conventional pure electric refrigeration systems for producing liquid air and existing LNG cold energy air liquefaction systems.

[0048] like Figure 2 and Figure 4As shown, in a feasible embodiment of the present invention, the LNG pressure regulating device includes an LNG throttling device 13 and a natural gas compressor 14. The LNG throttling device 13 is arranged upstream of the first heat exchanger 11, and the natural gas compressor 14 is arranged downstream of the second heat exchanger 12. The purpose of such arrangement is that the LNG gasification cycle unit is throttled first and then pressurized, and the LNG pressure energy is converted into high-grade temperature energy, such as throttling and reducing the pressure to 115kPa, making full use of the LNG temperature and quality. like Figure 3 As shown, in a feasible embodiment of the present invention, the LNG pressure regulating device includes a cryogenic pump 15 and a natural gas compressor 14, wherein the cryogenic pump 15 is arranged upstream of the first heat exchanger 11, and the natural gas compressor 14 is arranged downstream of the second heat exchanger 12. The purpose of such arrangement is that the cryogenic pump 15 can be used to increase the pressure to a certain pressure, and then the natural gas compressor 14 is used to compress it to reach the natural gas network pressure, or the cryogenic pump 15 can be used to increase the pressure to the natural gas network pressure, thereby eliminating the compression of the natural gas compressor 14, and the use of a cryogenic pump to pressurize the liquid has lower energy consumption than that of a gas compressor.

[0049] like Figure 1 and Figure 5 As shown, in a feasible embodiment of the present invention, the LNG pressure regulating device includes an LNG throttling device 13, a cryogenic pump 15 and an ejector 16, wherein the LNG throttling device 13 is arranged upstream of the first heat exchanger 11, the cryogenic pump 15 is arranged upstream of the first heat exchanger 11, and the ejector 16 is arranged downstream of the second heat exchanger 12. The purpose of such arrangement is that the small cryogenic pump 15 has low pressurization energy consumption, and after heat exchange and gasification with the refrigerant, the ejector 16 uses the pressure energy of the high-pressure natural gas to realize natural gas self-pressurization, and the energy consumption of natural gas pressurization is lower.

[0050] In a feasible embodiment of the present invention, the LNG gasification circulation unit 1 also includes a natural gas cooling device 17, which is arranged downstream of the natural gas compressor 14, and the outlet of the natural gas cooling device 17 is connected to the city gas pipeline network. The natural gas cooling device 17 is used to cool the natural gas to a required temperature.

[0051] In a feasible embodiment of the present invention, the air compressor 31 may be a multi-stage compression unit, and an air cooler 32 is provided downstream of each compression unit to improve the air liquefaction efficiency.

[0052] In a feasible embodiment of the present invention, the air pressurized liquefaction circulation unit 3 also includes an air drying purifier 34, which is arranged between the air cooler 32 and the third heat exchanger 33. The air drying purifier can achieve air purification in a variety of ways, so that the air is dehydrated and decarbonized before entering the third heat exchanger 33. These processes are completed in the cold dryer and the molecular sieve adsorber respectively, and then enter the third heat exchanger 33.

[0053] Furthermore, the air pressurized liquefaction circulation unit 3 includes an air inlet pipe and a liquid air outlet pipe, the air inlet pipe is connected to the input end of the air compressor 31, the liquid air outlet pipe is connected to the storage tank, or the liquid air outlet pipe is connected to the raw material inlet pipe for air separation, medical care, food processing, oxygen-enriched combustion and carbon capture, and energy storage system.

[0054] like Figure 4 The working principle of the embodiment shown is as follows: the original LNG enters the system from the storage tank, and after being throttled and cooled by the LNG throttling device 13, it enters the first heat exchanger 11 to exchange heat with argon. The LNG evaporates and the argon condenses to generate liquid argon. The evaporated LNG becomes NG and exchanges heat with the argon to recover cold energy. The temperature rises to -14°C and enters the first heat exchanger 11 to room temperature. Then the natural gas is pressurized to 0.4MPa by the natural gas compressor 14 and enters the low-pressure gas supply network. The raw air needs to be compressed, dehydrated and decarbonized before entering the low-temperature system, and then compressed to 0.4MPa in the first stage and 0.8MPa in the second stage and cooled separately. The produced liquid air can choose different storage pressures for the next separation or other purposes.

[0055] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0056] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "mode", "specific mode", or "some modes" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or mode are included in at least one embodiment or mode of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or mode. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or modes in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or modes described in this specification and the features of the different embodiments or modes, without contradiction.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and only the main components are illustrated in each circulation unit, rather than limiting them. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An LNG cold energy air liquefaction system based on a vapor compression heat pump cycle, characterized in that: include: An LNG gasification circulation unit (1) comprises a first heat exchanger (11), a second heat exchanger (12) and an LNG pressure regulating device; the first heat exchanger (11) is connected to an LNG storage tank; the LNG pressure regulating device is used to increase the pressure of the LNG; A vapor compression cold energy transfer heat pump circulation unit (2) having a circulating refrigerant flowing therein for recovering low-temperature cold energy of LNG liquid to liquefy air at a lower temperature; The air pressurization liquefaction circulation unit (3) comprises an air compressor (31), an air cooler (32) and a third heat exchanger (33) which are connected in sequence; and the third heat exchanger (33) is used for heat exchange between air and circulating refrigerant; The refrigerant gas cooling circulation unit (4) is used for recovering the sensible heat and cold energy of the gasified LNG and for cooling the gas compressed by the vapor compression cold energy transmission heat pump circulation unit (2) and the air pressurization liquefaction circulation unit (3).

2. The LNG cold energy air liquefaction system based on vapor compression heat pump cycle according to claim 1 is characterized in that: The vapor compression cold energy transfer heat pump circulation unit (2) is of cascade type, comprising a methane heat pump circulation loop (21) and an argon heat pump circulation loop (22), wherein the circulating refrigerants are methane and argon respectively; The methane heat pump circulation loop (21) comprises a loop formed by a first compressor (211), a first gas cooler (212), the first heat exchanger (11), a first gas throttle (213) and a fourth heat exchanger (214); methane is cooled by the first gas cooler (212) and the coolant gas cooling circulation unit (4); The argon heat pump circulation loop (22) comprises a loop formed by a second compressor (221), a second gas cooler (222), the fourth heat exchanger (214), a second gas throttle (223) and the third heat exchanger (33); the argon gas is cooled by the second gas cooler (222) and the refrigerant gas cooling circulation unit (4).

3. The LNG cold energy air liquefaction system based on vapor compression heat pump cycle according to claim 2 is characterized in that: The refrigerant gas cooling circulation unit (4) comprises a circuit formed by a refrigerant circulation pump (41), the second heat exchanger (12), a refrigerant flow divider (42) and a refrigerant flow combiner (43), and the air cooler (32), the first gas cooler (212) and the second gas cooler (222) are arranged in parallel between the refrigerant flow divider (42) and the refrigerant flow combiner (43).

4. The LNG cold energy air liquefaction system based on a vapor compression heat pump cycle according to any one of claims 1 to 3, characterized in that: The LNG pressure regulating device comprises an LNG throttling device (13) and a natural gas compressor (14); the LNG throttling device (13) is arranged upstream of the first heat exchanger (11), and the natural gas compressor (14) is arranged downstream of the second heat exchanger (12).

5. The LNG cold energy air liquefaction system based on vapor compression heat pump cycle according to any one of claims 1 to 3, characterized in that: The LNG pressure regulating device comprises a cryogenic pump (15) and a natural gas compressor (14); the cryogenic pump (15) is arranged upstream of the first heat exchanger (11), and the natural gas compressor (14) is arranged downstream of the second heat exchanger (12).

6. The LNG cold energy air liquefaction system based on a vapor compression heat pump cycle according to any one of claims 1 to 3, characterized in that: The LNG pressure regulating device comprises an LNG throttling device (13), a cryogenic pump (15) and an ejector (16); the LNG throttling device (13) and the cryogenic pump (15) are connected in parallel and are both arranged upstream of the first heat exchanger (11); and the ejector (16) is arranged downstream of the second heat exchanger (12).

7. The LNG cold energy air liquefaction system based on vapor compression heat pump cycle according to claim 3 is characterized in that: The coolant is a solution that remains in liquid state during circulation.

8. The LNG cold energy air liquefaction system based on vapor compression heat pump cycle according to claim 4 is characterized in that: The LNG gasification circulation unit (1) further comprises a natural gas cooling device (17), wherein the natural gas cooling device (17) is arranged downstream of the natural gas compressor (14), and an outlet of the natural gas cooling device (17) is connected to a city gas pipeline network.

9. The LNG cold energy air liquefaction system based on vapor compression heat pump cycle according to claim 8, characterized in that: The air compressor (31) is a multi-stage compression unit, and an air cooler (32) is provided downstream of each compression unit.

10. The LNG cold energy air liquefaction system based on vapor compression heat pump cycle according to claim 8, characterized in that: The air pressurized liquefaction circulation unit (3) further comprises an air drying purifier (34) which is arranged between the air cooler (32) and the third heat exchanger (33).

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