Refrigerating system adopting mixed precooling of LNG and liquid nitrogen and method thereof

Abstract

The invention relates to a refrigerating system adopting LNG and liquid nitrogen mixed precooling and a method thereof. The system comprises a raw material supply unit which comprises a raw material supply pipeline and is used for providing high-pressure raw material gas to be liquefied, and the raw material gas is at least one of hydrogen, helium or neon; the heat exchange unit comprises a plurality of precooling heat exchangers and a plurality of copious cooling heat exchangers which are connected in sequence; each heat exchanger is provided with a set inter-stage temperature zone; the raw material supply pipeline is sequentially connected with raw material inlets and outlets of the heat exchangers; the pre-cooling medium supply unit comprises an LNG supply pipeline and a liquid nitrogen supply pipeline, the LNG supply pipeline is at least connected with one pre-cooling heat exchanger, and the natural gas subjected to heat exchange with the pre-cooling heat exchanger is introduced into the natural gas recovery device; the liquid nitrogen supply pipeline is at least connected with other precooling heat exchangers so as to cool the feed gas to a first temperature based on the liquefied natural gas and the liquid nitrogen; the cryogenic medium supply unit is used for providing a low-temperature heat exchange medium for the cryogenic heat exchanger so as to cool the feed gas to 4-20K; and the Dewar is used for collecting the liquefied raw materials. The system is simple in structure, and the pre-cooling cost can be remarkably reduced.

Description

Technical Field

[0001] This invention relates to the field of cryogenic refrigeration technology, and in particular to a refrigeration system and method that uses a mixture of LNG and liquid nitrogen for precooling. Background Technology

[0002] Cryogenic technology, especially the acquisition and maintenance of deep cryogenic environments in the 2K to 20K temperature range, is a key cornerstone for the development of modern cutting-edge science and advanced engineering. It plays an irreplaceable role in fields such as cryogenic scientific devices (e.g., particle accelerators, nuclear fusion reactors), aerospace (e.g., space environment simulation, infrared detector cooling), quantum computing, and performance testing of high-end materials and devices.

[0003] Currently, in the aforementioned cryogenic applications ranging from 2K to 20K, the precooling medium typically employs an open-loop liquid nitrogen precooling cycle. The nitrogen gas at room temperature, having exhausted its cooling capacity, lacks economic recovery value and is generally released directly into the atmosphere, resulting in energy waste. Furthermore, direct use of liquid nitrogen for precooling leads to high liquid nitrogen consumption, requiring large-scale on-site storage and incurring significant storage and transportation costs. Therefore, while using liquid nitrogen as the precooling medium is technically feasible, its economic viability is poor and it can no longer meet the growing demand for cryogenic media in modern technological development.

[0004] Therefore, there is an urgent need for a refrigeration system and method that uses a mixture of LNG and liquid nitrogen for precooling to reduce refrigeration costs. Summary of the Invention

[0005] This invention provides a refrigeration system and method that uses a mixture of LNG and liquid nitrogen for precooling. The system has a simple structure and can significantly reduce precooling costs.

[0006] In a first aspect, embodiments of the present invention provide a refrigeration system employing a mixture of LNG and liquid nitrogen for pre-cooling, comprising: The raw material supply unit includes a raw material supply pipeline for supplying high-pressure raw material gas to be liquefied, wherein the raw material gas is at least one of hydrogen, helium or neon. The heat exchange unit includes multiple precooling heat exchangers and multiple cryogenic heat exchangers connected in sequence; each heat exchanger has a set interstage temperature zone; the raw material supply pipeline is connected in sequence to the raw material inlet and outlet of each heat exchanger. The precooling medium supply unit includes an LNG supply pipeline and a liquid nitrogen supply pipeline. The LNG supply pipeline is connected to at least one of the precooling heat exchangers, and the natural gas after heat exchange with the precooling heat exchanger is introduced into a natural gas recovery device. The liquid nitrogen supply pipeline is connected to at least other precooling heat exchangers to cool the feed gas to a first temperature based on liquefied natural gas and liquid nitrogen. A cryogenic medium supply unit is used to supply a low-temperature heat exchange medium to the cryogenic heat exchanger to cool the raw gas to 4-20K. The dewar, connected to the outlet of the raw material supply pipeline, is used to collect the liquefied raw material.

[0007] Secondly, embodiments of the present invention also provide a refrigeration method using a mixture of LNG and liquid nitrogen for pre-cooling, comprising: The raw material supply unit is used to provide the raw material gas to be liquefied; The LNG supply pipeline provides liquefied natural gas, and the liquid nitrogen supply pipeline provides liquid nitrogen, so that the liquefied natural gas and liquid nitrogen cool the feed gas to a first temperature in the corresponding precooling heat exchangers; The cryogenic medium supply unit provides a low-temperature heat exchange medium to the cryogenic heat exchanger to cool the raw gas to 4-20K. The liquefied raw materials are collected using the Dewar.

[0008] This application provides a refrigeration system and method employing a mixed precooling of LNG and liquid nitrogen. By incorporating a precooling heat exchanger and a cryogenic heat exchanger, precooling and cryogenic treatment of the feedstock gas to be liquefied are achieved. Furthermore, in the precooling stage, the use of a mixed precooling method with LNG and liquid nitrogen significantly reduces liquid nitrogen consumption by requiring only 1-2 additional heat exchanger stages. This system fully utilizes the cold energy of LNG while simultaneously returning ambient or cryogenic natural gas, which is then reintroduced into pipeline natural gas transportation, preventing the waste of LNG cold energy. Moreover, the combined precooling method optimizes the interstage temperature of each heat exchanger, reducing cold losses in the precooling section and improving refrigeration efficiency. Therefore, the system structure of this application is simple and can significantly reduce precooling costs. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of a refrigeration system using a mixture of LNG and liquid nitrogen for pre-cooling, provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a refrigeration system using a mixture of LNG and liquid nitrogen for pre-cooling, provided in another embodiment of the present invention; Figure 3 This is a schematic diagram of a system provided by an embodiment of the present invention, which involves mixing and pre-cooling LNG and liquid nitrogen for use in a liquefaction unit; Figure 4 This is a schematic diagram of a system for pre-cooling LNG and liquid nitrogen mixtures in a liquefaction unit, provided by another embodiment of the present invention. Figure 5 This is a schematic diagram of a refrigeration method using a mixture of LNG and liquid nitrogen for pre-cooling, provided by an embodiment of the present invention.

[0011] Figure label: 1-Raw material supply unit; 2-Heat exchange unit; 21-First-stage precooling heat exchanger; 22-Second-stage precooling heat exchanger; 23-Third-stage precooling heat exchanger; 24-Fourth-stage precooling heat exchanger; 25-Cryogenic heat exchanger; 3-Pre-cooling medium supply unit; 31-LNG supply pipeline; 32 - First branch road; 33 - Second branch road; 4-Cryogenic medium supply unit; 41-First expander; 42-Second expander; 5-Duwa; 6-Liquid nitrogen storage tank; 7-Return gas line; 8-Material supply pipes; 81 - Third Branch Road; 82 - Fourth Branch Road; 83 - Fifth Branch Road; 9-High-pressure refrigerant pipeline; 10 - Low-pressure refrigerant piping. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0013] like Figure 1 As shown, this embodiment of the invention provides a refrigeration system that uses a mixture of LNG and liquid nitrogen for pre-cooling. The system includes: The raw material supply unit 1 includes a raw material supply pipeline for supplying high-pressure raw material gas to be liquefied, wherein the raw material gas is at least one of hydrogen, helium or neon. The heat exchange unit 2 includes multiple precooling heat exchangers and multiple cryogenic heat exchangers 25 connected in sequence; each heat exchanger has a set interstage temperature zone; the raw material supply pipeline is connected in sequence to the raw material inlet and outlet of each heat exchanger. The precooling medium supply unit 3 includes an LNG supply pipeline 31 and a liquid nitrogen supply pipeline. The LNG supply pipeline 31 is connected to at least one of the precooling heat exchangers, and the natural gas after heat exchange with the precooling heat exchanger is introduced into a natural gas recovery device. The liquid nitrogen supply pipeline is connected to at least other precooling heat exchangers to cool the feed gas to a first temperature based on liquefied natural gas and liquid nitrogen. The cryogenic medium supply unit 4 is used to supply the cryogenic heat exchanger 25 with a low-temperature heat exchange medium to cool the raw gas to 4-20K. Dewar 5 is connected to the outlet of the raw material supply pipeline and is used to collect the liquefied raw material.

[0014] This system achieves pre-cooling and deep-cooling of the liquefied feedstock gas by incorporating pre-cooling and cryogenic heat exchangers. Furthermore, during the pre-cooling stage, the use of a mixed pre-cooling method with liquefied natural gas and liquid nitrogen significantly reduces liquid nitrogen consumption by requiring only one or two additional heat exchangers. This system fully utilizes the cold energy of liquefied natural gas while simultaneously returning ambient or cryogenic natural gas, which is then reintroduced into the pipeline, preventing waste of liquefied natural gas cold energy. Moreover, the combined pre-cooling approach optimizes the interstage temperature of each heat exchanger, reducing heat loss in the pre-cooling section and improving refrigeration efficiency. Therefore, the system presented in this application has a simple structure and can significantly reduce pre-cooling costs.

[0015] Furthermore, the preferred initial temperature is 80K, and the feedstock gas to be liquefied is ambient temperature gas. Additionally, this refrigeration system is preferably installed in scenarios requiring the utilization of LNG's cooling energy, such as LNG (liquefied natural gas) receiving terminals or LNG peak-shaving stations. In such scenarios, the LNG itself needs to be heated to saturated or ambient temperature natural gas, requiring heating devices. However, by using LNG as a pre-cooling medium, its cooling energy is fully utilized while obtaining the required natural gas product, reducing the investment in heating devices and achieving a win-win situation, thus preventing the waste of LNG's cooling energy.

[0016] In addition, the feed gas is a high-pressure gas with a pressure of approximately 0.8~3 MPa. Of course, the feed gas pressure is determined according to user requirements, and this application is not limited to this.

[0017] In some embodiments, along the direction of raw gas flow, the precooling heat exchanger includes a primary precooling heat exchanger 21, a secondary precooling heat exchanger 22, a tertiary precooling heat exchanger 23, and a quaternary precooling heat exchanger 24. One end of the LNG supply pipeline 31 is connected to the liquefied natural gas supply device, and the other end is connected to the natural gas recovery device after exchanging heat with the secondary precooling heat exchanger 22. The liquid nitrogen supply pipeline is connected in sequence to the fourth-stage precooling heat exchanger 24, the third-stage precooling heat exchanger 23 and the first-stage precooling heat exchanger 21.

[0018] This embodiment utilizes only the latent heat of LNG and is suitable for scenarios requiring the recovery of saturated natural gas.

[0019] In addition, such as Figure 1 As shown, the liquid nitrogen originates from the liquid nitrogen storage tank 6; the liquid nitrogen supply pipeline includes a first branch 32 and a second branch 33; wherein, One end of the first branch 32 is connected to the liquid phase space of the liquid nitrogen storage tank 6, and the other end is connected to the gas phase space of the liquid nitrogen storage tank 6 after exchanging heat with the four-stage precooling heat exchanger 24. One end of the second branch 33 is connected to the gas phase space of the liquid nitrogen storage tank 6, and the other end is connected to the outside after exchanging heat with the third-stage precooling heat exchanger 23 and the first-stage precooling heat exchanger 21 in sequence.

[0020] In addition, the refrigeration system also includes a return gas pipeline 7, one end of which is connected to the gas phase space of the Dewar 5, and the other end passes through the cryogenic heat exchanger 25, the tertiary precooling heat exchanger 23, the secondary precooling heat exchanger 22 and the primary precooling heat exchanger 21 in the opposite direction of the raw material gas flow.

[0021] In this step, the return gas pipeline 7 supplies low-pressure feedstock return gas. After being compressed by the compressor, the low-pressure feedstock return gas enters the feedstock supply pipeline and is recycled as high-pressure feedstock gas. In this way, not only can feedstock waste be avoided, but it can also be used as a cold source to cool the high-pressure feedstock gas, thereby improving energy utilization.

[0022] The first-stage precooling heat exchanger 21 uses cold nitrogen and low-pressure feed return gas to cool the feed gas to 145-155K; the second-stage precooling heat exchanger 22 uses LNG and low-pressure feed return gas together to cool the feed gas to 105-125K; the third-stage precooling heat exchanger 23 uses cold nitrogen to cool the feed gas to 83-90K; and the fourth-stage precooling heat exchanger 24 uses liquid nitrogen to cool the feed gas to 78-80K. By adding LNG precooling, the system divides the cooling of the feed gas from room temperature to 80K into four stages. Although the number of precooling heat exchangers increases by two, the overall heat load remains unchanged, resulting in minimal increase in heat exchanger costs. Furthermore, increasing the number of precooling heat exchangers to four stages increases the heat transfer gradient, which is beneficial for improving heat transfer efficiency.

[0023] It should be noted that the use of a four-stage precooling heat exchanger 24 here is only a preferred method. Users can also use more or fewer stages of heat exchangers as needed. This application is not limited to the above method.

[0024] In some implementations, such as Figure 2As shown, after exchanging heat with the secondary precooling heat exchanger 22, the LNG supply pipeline 31 is also connected to the primary precooling heat exchanger 21.

[0025] This precooling method can utilize both the latent heat and sensible heat of LNG, making it suitable for scenarios requiring the recovery of ambient temperature natural gas. In this connection configuration, the first-stage precooling heat exchanger 21 uses cold natural gas, cold nitrogen, and low-pressure feedstock return gas to cool the feedstock gas to 130-140K; the second-stage precooling heat exchanger 22 uses LNG and low-pressure feedstock return gas to cool the feedstock gas to 105-125K; the third-stage precooling heat exchanger 23 uses cold nitrogen and low-pressure feedstock return gas to cool the feedstock gas to 83-90K; and the fourth-stage precooling heat exchanger 24 uses liquid nitrogen to cool the feedstock gas to 78-80K. Similarly, by adding LNG precooling, the system divides the cooling of the feedstock gas from ambient temperature to 80K into four stages. Although the number of precooling heat exchangers increases by two, the overall heat load remains unchanged, resulting in minimal increase in heat exchanger costs. Simultaneously, the increased heat gradient improves heat exchange efficiency.

[0026] In some embodiments, the cryogenic medium supply unit 4 includes a first expander 41 and a second expander 42. The raw material medium flowing out from the first-stage cryogenic heat exchanger enters the first expander 41. The gas flowing out from the first expander 41 enters the second expander 42 after heat exchange by at least one subsequent cryogenic heat exchanger 25. The gas flowing out from the second expander 42 merges with the return gas pipeline 7.

[0027] This embodiment uses two turbine expanders to expand and cool the raw material medium to obtain a low-temperature medium. The low-temperature medium flows through the subsequent cryogenic heat exchanger 25 for heat exchange and then enters the second expander 42. The medium flowing out of the second expander 42 mixes with the low-pressure raw material return gas, which can realize the recovery and utilization of the raw material gas, reduce raw material loss, and serve as a cold source to cool the high-pressure raw material gas.

[0028] In some embodiments, the refrigeration system further includes a feed pipe 8, one end of which is connected to the liquid phase space of the Dewar 5, and the other end of which is divided into a third branch 81, a fourth branch 82 and a fifth branch 83 after heat exchange with the heat load. The third branch 81 is connected to the outlet return gas pipeline 7 of the first-stage precooling heat exchanger 21, the fourth branch 82 is connected to the return gas pipeline 7 between the second-stage precooling heat exchanger 22 and the third-stage precooling heat exchanger 23, and the fifth branch 83 is connected to the outlet return gas pipeline 7 of the Dewar 5.

[0029] This embodiment, by setting up a material supply pipe 8, can supply liquefied raw materials to heat users, thereby realizing energy utilization.

[0030] The inventors discovered that the aforementioned problems exist not only in refrigeration machines but also in liquefaction plants. Therefore, a system for combined precooling of LNG and liquid nitrogen can also be applied to liquefaction plants, such as hydrogen liquefaction plants, helium liquefaction plants, or neon liquefaction plants.

[0031] like Figure 3 and Figure 4 As shown, when LNG and liquid nitrogen are used together for precooling in a liquefaction plant, the precooling system also includes a high-pressure refrigerant pipeline 9 and a low-pressure refrigerant pipeline 10. The cryogenic medium supply unit 4 includes a first expander 41 and a second expander 42. The high-pressure refrigerant pipeline 9 is used to provide high-pressure refrigerant. The high-pressure refrigerant flows sequentially through the first-stage precooling heat exchanger 21, the second-stage precooling heat exchanger 22, the third-stage precooling heat exchanger 23, the fourth-stage precooling heat exchanger 24, and at least the first-stage cryogenic heat exchanger before entering the first expander 41. The gas flowing out of the first expander 41 is heat-exchanged by at least one subsequent cryogenic heat exchanger 25 before entering the second expander 42. The gas flowing out of the second expander 42 enters the low-pressure refrigerant pipeline 10. The low-pressure refrigerant in the low-pressure refrigerant pipeline 10 flows sequentially through each of the cryogenic heat exchangers 25, the third-stage precooling heat exchanger 23, the second-stage precooling heat exchanger 22, and the first-stage precooling heat exchanger 21 in the opposite direction to the flow direction of the raw material gas.

[0032] In the aforementioned liquefaction unit, the latent heat of liquefied natural gas can be utilized alone, or both latent and sensible heat can be utilized simultaneously. When only the latent heat of liquefied natural gas is utilized, such as... Figure 3 As shown, the first-stage precooling heat exchanger 21 uses cold nitrogen and cryogenic refrigerant (i.e., low-pressure refrigerant) return gas to cool the raw material gas and high-pressure refrigerant to 145-155K; the second-stage precooling heat exchanger 22 uses LNG and cryogenic refrigerant return gas together to cool the raw material gas and high-pressure refrigerant to 105-125K; the third-stage precooling heat exchanger 23 uses cold nitrogen, cryogenic refrigerant and cryogenic refrigerant return gas together to cool the raw material gas and high-pressure refrigerant to 83-90K; and the fourth-stage precooling heat exchanger 24 uses liquid nitrogen to cool the raw material gas and high-pressure refrigerant to 78-80K.

[0033] When both the latent heat and sensible heat of liquefied natural gas are utilized, such as Figure 4As shown, the first-stage precooling heat exchanger 21 uses cold natural gas, cold nitrogen, and cryogenic refrigerant return gas to cool the feed gas and high-pressure refrigerant to 130-140K; the second-stage precooling heat exchanger 22 uses LNG and cryogenic refrigerant return gas together to cool the feed gas and high-pressure refrigerant to 105-125K; the third-stage precooling heat exchanger 23 uses cold nitrogen, cryogenic refrigerant, and cryogenic refrigerant return gas together to cool the feed gas and high-pressure refrigerant to 83-90K; and the fourth-stage precooling heat exchanger 24 uses liquid nitrogen to cool the feed gas and high-pressure refrigerant to 78-80K.

[0034] It should also be noted that the feed gas for the liquefaction unit can be hydrogen, nitrogen, or neon. For any liquefaction unit, additional devices may be required depending on the properties of the feed gas. For example, a hydrogen liquefaction unit would require a hydrogen adsorber, isothermal converter, adiabatic converter, and throttling valve, etc., with installation locations as follows: Figure 3 and Figure 4 As shown. When applied to helium or neon liquefaction devices, adjustments should be made according to the properties of the gas, which will not be elaborated here.

[0035] It should be noted that users can also determine the temperature zone of each stage of precooling heat exchanger as needed; this application does not impose specific limitations.

[0036] To demonstrate the effectiveness of the method described in this application, the inventors calculated the above process. The results show that the refrigeration process using a mixture of liquid nitrogen and LNG for precooling reduces liquid nitrogen consumption by two-thirds compared to the process using only liquid nitrogen for precooling. Furthermore, for the LNG and liquid nitrogen mixed precooling process, the refrigeration process utilizing both latent and sensible heat of LNG significantly reduces LNG consumption by two-thirds compared to the process utilizing only the latent heat of LNG. Therefore, the system described in this application can significantly reduce liquid nitrogen consumption, making it particularly suitable for sites where liquid nitrogen transportation is inconvenient or far from large air separation units. This reduces the amount of liquid nitrogen stored on-site, resulting in significant economic benefits. Additionally, adding one or two stages of heat exchangers has little impact on the overall dimensions of the refrigeration system, and this optimized process has a minimal impact on equipment investment costs.

[0037] also, Figures 1-4 Only some of the equipment required to complete the refrigeration is shown. In addition, the system may also include other equipment required for normal operation, such as valves, pipes, adsorbers, isothermal converters, adiabatic converters, expansion valves, thermometers, and pressure gauges. These will not be described in detail here.

[0038] like Figure 5 As shown, this embodiment of the invention provides a refrigeration method using a mixture of LNG and liquid nitrogen for pre-cooling, the method comprising: Step 100: The raw material gas to be liquefied is provided using the raw material supply unit 1; Step 102: LNG supply pipeline 31 is used to supply liquefied natural gas, and liquid nitrogen is used to supply liquid nitrogen, so that the liquefied natural gas and liquid nitrogen are used to cool the raw gas to the first temperature in the corresponding precooling heat exchanger; Step 104: The cryogenic medium supply unit 4 is used to supply a low-temperature heat exchange medium to the cryogenic heat exchanger 25 to cool the raw gas to 4-20K. Step 106: Collect the liquefied raw materials using the Dewar 5.

[0039] It is understood that the refrigeration method using a mixture of LNG and liquid nitrogen for precooling provided in this embodiment has the same beneficial effects as the refrigeration system using a mixture of LNG and liquid nitrogen for precooling provided in the above embodiments, and will not be described in detail here.

[0040] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A refrigeration system employing a mixture of LNG and liquid nitrogen for pre-cooling, characterized in that, include: The raw material supply unit (1) includes a raw material supply pipeline for supplying high-pressure raw material gas to be liquefied, wherein the raw material gas is at least one of hydrogen, helium or neon. The heat exchange unit (2) includes multiple precooling heat exchangers and multiple cryogenic heat exchangers (25) connected in sequence; each heat exchanger has a set interstage temperature zone; the raw material supply pipeline is connected in sequence to the raw material inlet and outlet of each heat exchanger; The precooling medium supply unit (3) includes an LNG supply pipeline (31) and a liquid nitrogen supply pipeline. The LNG supply pipeline (31) is connected to at least one of the precooling heat exchangers, and the natural gas after heat exchange with the precooling heat exchanger is introduced into the natural gas recovery device. The liquid nitrogen supply pipeline is connected to at least other precooling heat exchangers to cool the raw gas to a first temperature based on liquefied natural gas and liquid nitrogen. The cryogenic medium supply unit (4) is used to supply the cryogenic heat exchanger (25) with a low-temperature heat exchange medium to cool the raw gas to 4-20K; Dewar (5) is connected to the outlet of the raw material supply pipeline and is used to collect the liquefied raw material.

2. The refrigeration system according to claim 1, characterized in that, Along the direction of raw gas flow, the precooling heat exchanger includes a primary precooling heat exchanger (21), a secondary precooling heat exchanger (22), a tertiary precooling heat exchanger (23), and a quaternary precooling heat exchanger (24). One end of the LNG supply pipeline (31) is connected to the liquefied natural gas supply device, and the other end is connected to the natural gas recovery device after exchanging heat with the secondary precooling heat exchanger (22). The liquid nitrogen supply pipeline is connected in sequence to the fourth-stage precooling heat exchanger (24), the third-stage precooling heat exchanger (23), and the first-stage precooling heat exchanger (21).

3. The refrigeration system according to claim 2, characterized in that, The liquid nitrogen comes from the liquid nitrogen storage tank (6); the liquid nitrogen supply pipeline includes a first branch (32) and a second branch (33); One end of the first branch (32) is connected to the liquid phase space of the liquid nitrogen storage tank (6), and the other end is connected to the gas phase space of the liquid nitrogen storage tank (6) after exchanging heat with the fourth-stage precooling heat exchanger (24). One end of the second branch (33) is connected to the gas phase space of the liquid nitrogen storage tank (6), and the other end is connected to the outside after exchanging heat with the third-stage precooling heat exchanger (23) and the first-stage precooling heat exchanger (21) in sequence.

4. The refrigeration system according to claim 3, characterized in that, The temperature range of the raw gas flowing out from the first-stage precooling heat exchanger (21) is 145~155K, the temperature range of the raw gas flowing out from the second-stage precooling heat exchanger (22) is 105-120K, the temperature range of the raw gas flowing out from the third-stage precooling heat exchanger (23) is 83-90K, and the temperature range of the raw gas flowing out from the fourth-stage precooling heat exchanger (24) is 78-80K.

5. The refrigeration system according to claim 2, characterized in that, After exchanging heat with the secondary precooling heat exchanger (22), the LNG supply pipeline (31) is also connected to the primary precooling heat exchanger (21); The temperature range of the raw material gas flowing out from the first-stage precooling heat exchanger (21) is 130~140K, the temperature range of the raw material gas flowing out from the second-stage precooling heat exchanger (22) is 105-125K, the temperature range of the raw material gas flowing out from the third-stage precooling heat exchanger (23) is 83-90K, and the temperature range of the raw material gas flowing out from the fourth-stage precooling heat exchanger (24) is 78-80K.

6. The refrigeration system according to claim 2, characterized in that, It also includes a return gas pipeline (7), one end of which is connected to the gas phase space of the Dewar (5), and the other end passes through the cryogenic heat exchanger (25), the tertiary precooling heat exchanger (23), the secondary precooling heat exchanger (22) and the primary precooling heat exchanger (21) in the opposite direction of the raw material gas flow.

7. The refrigeration system according to claim 6, characterized in that, The cryogenic medium supply unit (4) includes a first expander (41) and a second expander (42). The raw material medium flowing out from the first stage cryogenic heat exchanger enters the first expander (41). The gas flowing out from the first expander (41) enters the second expander (42) after heat exchange by at least one subsequent cryogenic heat exchanger (25). The gas flowing out from the second expander (42) merges with the return gas pipeline (7).

8. The refrigeration system according to claim 6, characterized in that, It also includes a material pipeline (8), one end of which is connected to the liquid phase space of the Dewar (5), and the other end is connected to the heat load and then divided into a third branch (81), a fourth branch (82) and a fifth branch (83). The third branch (81) is connected to the outlet return gas pipeline (7) of the first-stage precooling heat exchanger (21), the fourth branch (82) is connected to the return gas pipeline (7) between the second-stage precooling heat exchanger (22) and the third-stage precooling heat exchanger (23), and the fifth branch (83) is connected to the outlet return gas pipeline (7) of the Dewar (5).

9. The refrigeration system according to claim 2, characterized in that, It also includes a high-pressure refrigerant pipeline (9) and a low-pressure refrigerant pipeline (10); the cryogenic medium supply unit (4) includes a first expander (41) and a second expander (42); The high-pressure refrigerant pipeline (9) is used to provide high-pressure refrigerant. The high-pressure refrigerant flows sequentially through the first-stage precooling heat exchanger (21), the second-stage precooling heat exchanger (22), the third-stage precooling heat exchanger (23), the fourth-stage precooling heat exchanger (24), and at least the first-stage cryogenic heat exchanger before entering the first expander (41). The gas flowing out of the first expander (41) is heat-exchanged by at least one subsequent cryogenic heat exchanger (25) before entering the second expander (42). The gas flowing out of the second expander (42) enters the low-pressure refrigerant pipeline (10). The low-pressure refrigerant in the low-pressure refrigerant pipeline (10) flows sequentially through each of the cryogenic heat exchangers (25), the third-stage precooling heat exchangers (23), the second-stage precooling heat exchangers (22), and the first-stage precooling heat exchangers (21) in the opposite direction to the flow direction of the raw material gas.

10. A refrigeration method employing a mixture of LNG and liquid nitrogen for pre-cooling, characterized in that, The method, applied to the refrigeration system using a mixture of LNG and liquid nitrogen for precooling as described in any one of claims 1-9, comprises: The raw material gas to be liquefied is provided by the raw material supply unit (1); Liquefied natural gas is supplied via the LNG supply pipeline (31), and liquid nitrogen is supplied via the liquid nitrogen supply pipeline, so that the liquefied natural gas and liquid nitrogen are used to cool the feed gas to a first temperature in the corresponding precooling heat exchangers; The cryogenic medium supply unit (4) provides a low-temperature heat exchange medium to the cryogenic heat exchanger (25) to cool the raw gas to 4-20K; The liquefied raw materials are collected using the Dewar (5).

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