A compact liquefaction device

Abstract

The application discloses a small-sized liquefaction device. A raw material gas pretreatment unit is provided with a raw material gas inlet, a purified gas outlet and a recovery gas inlet; a refrigeration liquefaction unit is provided with a liquefied natural gas outlet connected to an inlet of a storage and delivery unit; the storage and delivery unit comprises an LNG storage tank, a BOG treatment system and a delivery device, an inlet of the LNG storage tank is connected to the liquefied natural gas outlet of the refrigeration liquefaction unit, a first outlet thereof is connected to an inlet of the BOG treatment system, and a second outlet thereof is connected to the delivery device; the BOG treatment system is provided with a recovery gas outlet connected to the recovery gas inlet of the raw material gas pretreatment unit; and a control unit is electrically connected with the raw material gas pretreatment unit, the refrigeration liquefaction unit and the storage and delivery unit. The device has the characteristics of simple and compact equipment, low investment cost, flexible movement, short construction period and low energy consumption, and can efficiently treat scattered gas sources such as small gas fields, remote gas wells and oilfield associated gas.

Description

Technical Field

[0001] This application relates to the field of natural gas technology, and more particularly to a small liquefaction device. Background Technology

[0002] Natural gas is a clean energy source, and its liquefaction (LNG) is an important way to facilitate storage and transportation.

[0003] However, traditional natural gas liquefaction plants are large in scale, requiring extensive land areas; their complex processes make operation and maintenance difficult; high investment costs and long construction periods increase project risks and financial pressure; and their high energy consumption further increases operating costs. These factors make traditional plants unsuitable for the development and utilization of small-scale gas sources such as small gas fields, remote gas wells, and associated gas from oil fields, resulting in a large amount of scattered small-scale natural gas resources being idled and wasted, unable to be effectively converted into clean energy supply. Utility Model Content

[0004] This application provides a small-scale liquefaction device, which solves the problems mentioned in the background art.

[0005] This application provides a small-scale liquefaction device, including a skid and a feed gas pretreatment unit, a refrigeration liquefaction unit, a storage and export unit, and a control unit integrated on the skid. The feed gas pretreatment unit has a feed gas inlet, a purified gas outlet, and a recovered gas inlet. The feed gas inlet is used to input feed gas, and the purified gas outlet is connected to the inlet of the refrigeration liquefaction unit. The refrigeration liquefaction unit has a liquefied natural gas outlet connected to the inlet of the storage and export unit. The storage and export unit includes an LNG storage tank, a BOG processing system, and export equipment. The inlet of the LNG storage tank is connected to the liquefied natural gas outlet of the refrigeration liquefaction unit, its first outlet is connected to the inlet of the BOG processing system, and its second outlet is connected to the export equipment. The BOG processing system has a recovered gas outlet connected to the recovered gas inlet of the feed gas pretreatment unit. The control unit is electrically connected to the feed gas pretreatment unit, the refrigeration liquefaction unit, and the storage and export unit, and is used to monitor and regulate at least one process parameter among temperature, pressure, flow rate, and liquid level.

[0006] In one possible implementation, the raw gas pretreatment unit includes a raw gas compressor, a desulfurization and decarbonization unit, and a dehydration unit; the inlet of the raw gas compressor includes a raw gas inlet and a recovered gas inlet for pressurizing the raw gas; the inlet of the desulfurization and decarbonization unit is connected to the outlet of the raw gas compressor for removing hydrogen sulfide and carbon dioxide; the dehydration unit is internally equipped with a molecular sieve, and its inlet is connected to the first outlet of the desulfurization and decarbonization unit for deep removal of moisture; the first outlet of the dehydration unit is a purified gas outlet for outputting purified natural gas and is connected to the inlet of the refrigeration liquefaction unit.

[0007] In one possible implementation, the raw gas pretreatment unit further includes a mercury removal unit; the inlet of the mercury removal unit is connected to the second outlet of the desulfurization and decarbonization unit, and its outlet is connected to the second inlet of the dehydration unit.

[0008] In one possible implementation, the feed gas pretreatment unit further includes a heavy hydrocarbon separator; the inlet of the heavy hydrocarbon separator is connected to the third outlet of the desulfurization and decarbonization unit, and its outlet is connected to the third inlet of the dehydration unit.

[0009] In one possible implementation, the refrigeration and liquefaction unit includes a precooling heat exchanger, a cryogenic heat exchanger, and a mixed refrigerant circulation system. The hot channel inlet of the precooling heat exchanger is connected to the purified gas outlet of the feed gas pretreatment unit, and is used to precool the purified feed gas from ambient temperature to -20°C to -40°C. The hot channel inlet of the cryogenic heat exchanger is connected to the hot channel outlet of the precooling heat exchanger, and its hot channel outlet is used to output liquefied natural gas. The mixed refrigerant circulation system includes a refrigerant compressor, a refrigerant cooler, a cold channel of the cryogenic heat exchanger, a throttle valve, and a gas-liquid system connected sequentially along the mixed refrigerant flow direction. The refrigerant compressor is used to compress the mixed refrigerant; the refrigerant cooler is used to cool the compressed mixed refrigerant to below 40°C; the cold passage of the cryogenic heat exchanger is used to condense the high-pressure mixed refrigerant; the throttling valve is located at the outlet of the cold passage of the cryogenic heat exchanger and is used to throttle and expand the condensed high-pressure mixed refrigerant to generate a low-temperature cold source; the inlet of the gas-liquid separator is connected to the outlet of the throttling valve and is used to separate the refrigerant gas-liquid mixture formed after throttling; the gas phase outlet of the gas-liquid separator is connected to the inlet of the refrigerant compressor to realize the recycling of the mixed refrigerant.

[0010] In one possible implementation, the refrigeration liquefaction unit further includes a subcooling heat exchanger, the inlet of which is connected to the hot passage outlet of the cryogenic heat exchanger, and the outlet of which is connected to the inlet of the LNG storage tank.

[0011] In one possible implementation, the recovered gas outlet of the BOG processing system is also connected to the cold aisle inlet of the precooling heat exchanger.

[0012] In one possible implementation, the BOG processing system includes a BOG buffer tank and a BOG compressor; the inlet of the BOG buffer tank is connected to the first outlet of the LNG storage tank, and its outlet is connected to the inlet of the BOG compressor; the first outlet of the BOG compressor is connected to the recovery gas inlet of the feed gas pretreatment unit, and its second outlet is connected to the cold aisle inlet of the precooling heat exchanger.

[0013] In one possible implementation, the export equipment includes one or more of an LNG loading arm, a Dewar bottle filling gun, and a vaporizer.

[0014] In one possible implementation, the precooling heat exchanger is a shell-and-tube heat exchanger or a plate-fin heat exchanger; the cryogenic heat exchanger is a plate-fin heat exchanger.

[0015] One or more technical solutions provided in the embodiments of this application have at least the following technical effects: The small-scale liquefaction unit provided in this application, through a highly integrated skid-mounted design, compactly arranges the feed gas pretreatment unit, refrigeration liquefaction unit, storage and export unit, and control unit on the same skid. This effectively overcomes the shortcomings of traditional liquefaction units, such as large scale, large footprint, complex processes, high investment, high energy consumption, and difficulty in adapting to small-scale gas sources. This unit features simple and compact equipment, low investment cost, flexible mobility, short construction period, and low energy consumption. It can efficiently process dispersed gas sources such as small gas fields, remote gas wells, and associated gas from oil fields, reducing operating costs, improving clean energy utilization, and achieving economical and flexible liquefaction utilization of small-scale natural gas resources. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of the small liquefaction device provided in the embodiments of this application; Figure 2 This is a schematic diagram of the structure of the mixed refrigerant cycle system provided in the embodiments of this application.

[0018] Icons: 1-Bottom Skid; 2-Raw Gas Pretreatment Unit; 21-Raw Gas Compressor; 211-Raw Gas Inlet; 212-Recovered Gas Inlet; 22-Desulfurization and Decarbonization Unit; 23-Dehydration Unit; 231-Purified Gas Outlet; 24-Mercury Removal Unit; 25-Heavy Hydrocarbon Separator; 3-Refrigeration and Liquefaction Unit; 31-Precooling Heat Exchanger; 32-Cryogenic Heat Exchanger; 33-Mixed Refrigerant Circulation System; 331-Refrigerator Compressor; 332-Refrigerator Cooler; 333-Throttle Valve; 334-Gas-Liquid Separator; 34-Subcooling Heat Exchanger; 4-Storage and Export Unit; 41-LNG Storage Tank; 42-BOG Processing System; 421-BOG Buffer Tank; 422-BOG Compressor; 43-Export Equipment; 5-Control Unit. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In the description of the embodiments of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0021] This application provides a small liquefaction device, such as... Figures 1 to 2As shown. This small-scale liquefaction unit includes a skid 1, and a feed gas pretreatment unit 2, a refrigeration liquefaction unit 3, a storage and export unit 4, and a control unit 5 integrated on the skid 1. The feed gas pretreatment unit 2 is provided with a feed gas inlet 211, a purified gas outlet 231, and a recovery gas inlet 212. The feed gas inlet 211 is used to input feed gas, and the purified gas outlet 231 is connected to the inlet of the refrigeration liquefaction unit 3. The refrigeration liquefaction unit 3 is provided with a liquefied natural gas outlet, which is connected to the inlet of the storage and export unit 4. The storage and export unit 4 includes an LNG storage tank 41, a BOG (Boil-Off Gas) processing system 42, and an export device 43. The inlet of the LNG storage tank 41 is connected to the liquefied natural gas outlet of the refrigeration liquefaction unit 3, its first outlet is connected to the inlet of the BOG (Boil-Off Gas) processing system 42, and its second outlet is connected to the export device 43. The BOG processing system 42 is provided with a recovery gas outlet, which is connected to the recovery gas inlet 212 of the feed gas pretreatment unit 2. Control unit 5 is electrically connected to raw gas pretreatment unit 2, refrigeration liquefaction unit 3, and storage and output unit 4, and is used to monitor and regulate at least one process parameter among temperature, pressure, flow rate, and liquid level. Control unit 5 of this application adopts a DCS (Distributed Control System) and integrates a safety interlock system; when abnormal operating conditions are detected, including abnormal raw gas pressure, excessively low temperature of precooling heat exchanger 31, cryogenic heat exchanger 32, or subcooling heat exchanger 34, and excessively high pressure in LNG storage tank 41, the safety interlock system can automatically trigger protective operations, including closing corresponding valves, adjusting medium flow rate, or initiating safety venting, thereby ensuring continuous, stable, and safe operation of the unit.

[0022] Specifically, the LNG storage tank 41 used in this application is a vacuum-insulated storage tank with a design volume ranging from 5 to 50 cubic meters. It employs a skid-mounted structure for ease of movement and installation. The inner wall of the LNG storage tank 41 is made of stainless steel to resist the low-temperature corrosion of LNG; the outer wall is made of carbon steel, with a middle layer filled with high-efficiency insulation materials such as perlite or glass wool, maintaining a vacuum state to greatly reduce the transfer of external heat. This LNG storage tank 41 has excellent insulation performance, with a static evaporation rate of no more than 0.3% per day, effectively reducing LNG evaporation loss and ensuring the economic efficiency and safety of storage.

[0023] It should be noted that the small-scale liquefaction unit provided in this application embodiment, through a highly integrated skid-mounted design, compactly arranges the raw gas pretreatment unit 2, refrigeration liquefaction unit 3, storage and external transmission unit 4, and control unit 5 on the same skid 1. This effectively overcomes the shortcomings of traditional liquefaction units, which are large in scale, occupy a large area, have complex processes, high investment, high energy consumption, and are difficult to adapt to small-scale gas sources. This unit features simple and compact equipment, low investment cost, flexible mobility, short construction period, and low energy consumption. It can efficiently process dispersed gas sources such as small gas fields, remote gas wells, and associated gas from oil fields, reduce operating costs, improve the utilization rate of clean energy, and realize the economical and flexible liquefaction utilization of small-scale natural gas resources.

[0024] In this embodiment, the raw gas pretreatment unit 2 includes a raw gas compressor 21, a desulfurization and decarbonization unit 22, and a dehydration unit 23. The inlet end of the raw gas compressor 21 includes a raw gas inlet 211 and a recovery gas inlet 212, which are used to pressurize the raw gas. The raw gas compressor 21 in this application is a reciprocating compressor.

[0025] The inlet of the desulfurization and decarbonization unit 22 is connected to the outlet of the raw gas compressor 21 for removing hydrogen sulfide and carbon dioxide. The dehydration unit 23 is internally equipped with a molecular sieve, and its inlet is connected to the first outlet of the desulfurization and decarbonization unit 22 for deep moisture removal. The first outlet of the dehydration unit 23 is the purified gas outlet 231, used to output purified natural gas and connected to the inlet of the refrigeration liquefaction unit 3. The dehydration unit 23 of this application is internally filled with a 3A or 4A type molecular sieve as an adsorbent. This molecular sieve has a uniform pore size of 0.3-0.4 nm and can selectively adsorb water molecules, thereby achieving deep dehydration of the raw gas.

[0026] Specifically, the raw material gas compressor 21 increases the pressure of the raw material gas to the operating pressure required for subsequent purification and liquefaction processes (small liquefaction units are typically 3.0-8.0 MPa, depending on the refrigeration technology), ensuring stable gas flow in the process.

[0027] It should be noted that the raw gas pretreatment unit 2 in this embodiment effectively removes key impurities such as moisture, hydrogen sulfide, and carbon dioxide from the raw gas through the integrated setup and coordinated operation of the raw gas compressor 21, desulfurization and decarbonization unit 22, and dehydration unit 23. This avoids the risks of equipment freezing, corrosion, and LNG product quality degradation during subsequent liquefaction processes. This unit uses compression and pressurization to ensure stable flow, and combines efficient desulfurization, decarbonization, and deep dehydration processes (such as molecular sieve adsorption) to ensure that the purified raw gas meets the stringent requirements for liquefaction. This provides a clean and reliable gas source for the subsequent efficient and stable liquefaction process, making it a crucial pre-processing step for the long-term stable operation of the entire small-scale liquefaction unit.

[0028] In this embodiment, the raw gas pretreatment unit 2 further includes a mercury removal unit 24. The inlet of the mercury removal unit 24 is connected to the second outlet of the desulfurization and decarbonization unit 22, and its outlet is connected to the second inlet of the dehydration unit 23.

[0029] It should be noted that if the feed gas contains mercury (such as natural gas from some gas fields, where mercury can corrode aluminum heat exchangers), a "mercury removal tower" needs to be added after dehydration. Sulfur-based adsorbents (such as sulfur-loaded activated carbon) or precious metal adsorbents are used to reduce the mercury content to an extremely low level that meets the requirements for deep purification.

[0030] In this embodiment, the raw gas pretreatment unit 2 further includes a heavy hydrocarbon separator 25. The inlet of the heavy hydrocarbon separator 25 is connected to the third outlet of the desulfurization and decarbonization unit 22, and its outlet is connected to the third inlet of the dehydration unit 23.

[0031] It should be noted that if the raw gas contains... High levels of heavy hydrocarbons (such as associated gas from oil fields) cause these components to condense before methane during liquefaction, easily forming a liquid film on the heat exchanger surface. This significantly reduces heat transfer efficiency and can even cause pipe blockage. To avoid this problem, a heavy hydrocarbon separator 25 needs to be added after the desulfurization and decarbonization unit 22. An external cold source cools the gas flow to a range of 10-20°C, causing the heavy hydrocarbons to condense into a liquid state and separate. The separated heavy hydrocarbons can be recovered as byproducts such as liquefied petroleum gas (LPG), ensuring that the gas entering the subsequent refrigeration and liquefaction unit 3 is... The heavy hydrocarbon content is no higher than 0.1%, ensuring efficient and stable operation of the liquefaction process.

[0032] In this embodiment, the refrigeration liquefaction unit 3 includes a precooling heat exchanger 31, a cryogenic heat exchanger 32, and a mixed refrigerant circulation system 33. The hot channel inlet of the precooling heat exchanger 31 is connected to the purified gas outlet 231 of the raw material gas pretreatment unit 2, and is used to precool the purified raw material gas from room temperature to -20℃ to -40℃. The precooling cold source can be the first mixed refrigerant or the gas from the second outlet of the BOG compressor 422.

[0033] The hot aisle inlet of the cryogenic heat exchanger 32 connects to the hot aisle outlet of the precooling heat exchanger 31, and its hot aisle outlet is used to output liquefied natural gas. The mixed refrigerant circulation system 33 includes a refrigerant compressor 331, a refrigerant cooler 332, the cold aisle of the cryogenic heat exchanger 32, a throttle valve 333, and a gas-liquid separator 334, connected sequentially along the mixed refrigerant flow direction. The refrigerant compressor 331 is used to compress the mixed refrigerant. For example... Figure 2The second mixed refrigerant shown is a mixed refrigerant. The refrigerant cooler 332 is used to cool the compressed mixed refrigerant to below 40°C before it enters the subsequent condensation stage. The cold passage of the cryogenic heat exchanger 32 is used to condense the high-pressure mixed refrigerant. A throttling valve 333 is located at the outlet of the cold passage of the cryogenic heat exchanger 32 to throttle and expand the condensed high-pressure mixed refrigerant to generate a low-temperature cold source. The inlet of the gas-liquid separator 334 is connected to the outlet of the throttling valve 333 to separate the refrigerant gas-liquid mixture formed after throttling. The gas phase outlet of the gas-liquid separator 334 is connected to the inlet of the refrigerant compressor 331, enabling the recycling of the mixed refrigerant.

[0034] Furthermore, the pre-cooled purified raw gas (-20℃ to -40℃) enters the hot channel inlet of the cryogenic heat exchanger 32, where it exchanges heat counter-currently with the low-temperature mixed refrigerant (-150℃ to -170℃), and the temperature gradually decreases. First, the temperature is lowered from -40℃ to -100℃ (to remove some light hydrocarbon impurities); Then, the temperature is lowered from -100℃ to -162℃ (the normal boiling point of methane), at which point the natural gas completely condenses into liquid LNG.

[0035] Specifically, the composition of the second mixed refrigerant in this application is optimized and adjusted according to the feed gas composition and liquefaction temperature requirements, typically including methane, ethane, propane, butane, and nitrogen. Methane is primarily used to provide cooling capacity in the cryogenic section, while nitrogen is used to adjust the boiling point range of the refrigerant. The proportions of each component are precisely optimized through process calculations, for example, methane accounts for 30%-40%, propane for 20%-30%, and nitrogen for 5%-10%. Its core principle lies in utilizing the phase change (condensation and evaporation) that occurs when multiple refrigerants are mixed in specific proportions across different temperature ranges, thereby efficiently and continuously absorbing and releasing cooling capacity over a wide temperature range. Compared to traditional single-refrigerant cycles (such as pure propane or ethylene refrigeration), this mixed refrigerant cycle system 33 can achieve a more significant energy consumption reduction (up to 20%-30%), while also having a more compact system structure, making it particularly suitable for small liquefaction plants.

[0036] In this embodiment, the refrigeration liquefaction unit 3 further includes a subcooling heat exchanger 34, whose inlet is connected to the hot channel outlet of the cryogenic heat exchanger 32, and whose outlet is connected to the inlet of the LNG storage tank 41.

[0037] It should be noted that the subcooling heat exchanger 34 further cools the freshly liquefied LNG (-162℃, saturated liquid under normal pressure) to -165 to -170℃, making it a "subcooled liquid", which reduces the evaporation rate (BOG rate) of LNG during storage and improves storage stability.

[0038] In this embodiment of the application, the recovered gas outlet of the BOG processing system 42 is also connected to the cold aisle inlet of the precooling heat exchanger 31.

[0039] In this embodiment, the BOG processing system 42 includes a BOG buffer tank 421 and a BOG compressor 422. The inlet of the BOG buffer tank 421 is connected to the first outlet of the LNG storage tank 41, and its outlet is connected to the inlet of the BOG compressor 422. The first outlet of the BOG compressor 422 is connected to the recovery gas inlet 212 of the feed gas pretreatment unit 2, and its second outlet is connected to the cold aisle inlet of the precooling heat exchanger 31.

[0040] It should be noted that after the BOG compressor 422 pressurizes the collected BOG, one path flows back to the recovery gas inlet 212 of the raw material gas pretreatment unit 2 through the first outlet as a supplement to the raw material gas; the other path is delivered to the cold aisle inlet of the precooling heat exchanger 31 through the second outlet to provide fuel gas for the heating equipment in the unit (such as the regeneration tower and the subcooling heat exchanger 34), thereby realizing the effective recovery of BOG and comprehensive energy utilization.

[0041] In this embodiment, the export equipment 43 includes one or more of the following: an LNG loading arm, a Dewar bottle filling gun, and a vaporizer. It can be flexibly selected and configured according to actual application scenarios and user needs to meet various terminal export requirements such as tank truck transportation, bottled filling, or direct vaporization export.

[0042] In this embodiment, the precooling heat exchanger 31 is a shell-and-tube heat exchanger or a plate-fin heat exchanger. The cryogenic heat exchanger 32 is a plate-fin heat exchanger. Plate-fin heat exchangers have significant advantages such as compact structure, small size, and high heat exchange efficiency, and their application is particularly suitable for the small skid-mounted integrated liquefaction plant described in this application.

[0043] The small-scale liquefaction unit provided in this application offers significant economic and flexibility advantages for gas sources with a daily processing capacity of 10,000 standard cubic meters. It features low initial investment costs and a short payback period, recovering the entire investment cost within 10 to 14 months. In terms of space utilization, the unit itself has a compact structure, occupying only about 120 square meters; the total project area, including operation and maintenance space, is approximately 750 square meters, far smaller than traditional liquefaction plants. The entire unit adopts a highly integrated modular skid-mounted design, achieving excellent mobility. This design allows the unit to be manufactured and tested entirely in the factory, significantly shortening the on-site delivery and installation cycle. Simultaneously, the skid-mounted structure makes transportation and relocation extremely convenient, allowing for flexible relocation and rapid secondary construction based on changes in gas source distribution or project needs, greatly reducing on-site installation workload and construction time. It is particularly suitable for on-site liquefaction and utilization of various dispersed gas sources, such as well sites and remote areas.

[0044] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0045] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application 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 or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A small-scale liquefaction device, characterized in that, It includes a skid (1), and a raw gas pretreatment unit (2), a refrigeration liquefaction unit (3), a storage and export unit (4) and a control unit (5) integrated on the skid (1); The raw gas pretreatment unit (2) is provided with a raw gas inlet (211), a purified gas outlet (231) and a recovery gas inlet (212). The raw gas inlet (211) is used to input raw gas, and the purified gas outlet (231) is connected to the inlet of the refrigeration liquefaction unit (3). The refrigeration liquefaction unit (3) is provided with a liquefied natural gas outlet, which is connected to the inlet of the storage and export unit (4); the storage and export unit (4) includes an LNG storage tank (41), a BOG processing system (42) and an export device (43). The inlet of the LNG storage tank (41) is connected to the liquefied natural gas outlet of the refrigeration liquefaction unit (3), its first outlet is connected to the inlet of the BOG processing system (42), and its second outlet is connected to the export device (43). The BOG processing system (42) is provided with a recovery gas outlet, which is connected to the recovery gas inlet (212) of the raw material gas pretreatment unit (2). The control unit (5) is electrically connected to the raw gas pretreatment unit (2), the refrigeration liquefaction unit (3) and the storage and output unit (4), and is used to monitor and regulate at least one of the process parameters, including temperature, pressure, flow rate and liquid level.

2. The small-scale liquefaction device according to claim 1, characterized in that, The raw gas pretreatment unit (2) includes a raw gas compressor (21), a desulfurization and decarbonization unit (22), and a dehydration unit (23). The inlet end of the raw material gas compressor (21) includes the raw material gas inlet (211) and the recovery gas inlet (212), which are used to pressurize the raw material gas; The inlet of the desulfurization and decarbonization unit (22) is connected to the outlet of the raw material gas compressor (21) for removing hydrogen sulfide and carbon dioxide; The dehydration unit (23) is equipped with a molecular sieve, the inlet of which is connected to the first outlet of the desulfurization and decarbonization unit (22) for deep removal of moisture; The first outlet of the dehydration unit (23) is a purified gas outlet (231), which is used to output purified natural gas and is connected to the inlet of the refrigeration liquefaction unit (3).

3. The small-scale liquefaction device according to claim 2, characterized in that, The raw gas pretreatment unit (2) also includes a mercury removal unit (24); The inlet of the mercury removal unit (24) is connected to the second outlet of the desulfurization and decarbonization unit (22), and its outlet is connected to the second inlet of the dehydration unit (23).

4. The small-scale liquefaction device according to claim 2, characterized in that, The feed gas pretreatment unit (2) also includes a heavy hydrocarbon separator (25); The inlet of the heavy hydrocarbon separator (25) is connected to the third outlet of the desulfurization and decarbonization unit (22), and its outlet is connected to the third inlet of the dehydration unit (23).

5. The small-scale liquefaction device according to claim 1, characterized in that, The refrigeration liquefaction unit (3) includes a precooling heat exchanger (31), a cryogenic heat exchanger (32), and a mixed refrigerant circulation system (33). The inlet of the heat channel of the precooling heat exchanger (31) is connected to the outlet (231) of the purified gas of the raw material gas pretreatment unit (2), and is used to precool the purified raw material gas from room temperature to -40℃ to -20℃. The thermal channel inlet of the cryogenic heat exchanger (32) is connected to the thermal channel outlet of the precooling heat exchanger (31), and its thermal channel outlet is used to output liquefied natural gas. The mixed refrigerant circulation system (33) includes a refrigerant compressor (331), a refrigerant cooler (332), a cold passage of the cryogenic heat exchanger (32), a throttle valve (333), and a gas-liquid separator (334) connected in sequence along the mixed refrigerant flow direction. The refrigerant compressor (331) is used to compress the mixed refrigerant; The refrigerant cooler (332) is used to cool the compressed mixed refrigerant to below 40°C; The cold passage of the cryogenic heat exchanger (32) is used to condense high-pressure mixed refrigerant; The throttling valve (333) is located at the cold aisle outlet of the cryogenic heat exchanger (32) and is used to throttle and expand the condensed high-pressure mixed refrigerant to generate a low-temperature cold source. The inlet of the gas-liquid separator (334) is connected to the outlet of the throttle valve (333) for separating the refrigerant gas-liquid mixture formed after throttling; The gas phase outlet of the gas-liquid separator (334) is connected to the inlet of the refrigerant compressor (331) to realize the recycling of the mixed refrigerant.

6. The small-scale liquefaction device according to claim 5, characterized in that, The refrigeration liquefaction unit (3) also includes a subcooling heat exchanger (34), whose inlet is connected to the hot channel outlet of the cryogenic heat exchanger (32) and whose outlet is connected to the inlet of the LNG storage tank (41).

7. The small-scale liquefaction device according to claim 5, characterized in that, The recovered gas outlet of the BOG processing system (42) is also connected to the cold aisle inlet of the precooling heat exchanger (31).

8. The small-scale liquefaction device according to claim 7, characterized in that, The BOG processing system (42) includes a BOG buffer tank (421) and a BOG compressor (422). The inlet of the BOG buffer tank (421) is connected to the first outlet of the LNG storage tank (41), and its outlet is connected to the inlet of the BOG compressor (422); The first outlet of the BOG compressor (422) is connected to the recovery gas inlet (212) of the raw material gas pretreatment unit (2), and its second outlet is connected to the cold aisle inlet of the precooling heat exchanger (31).

9. The small-scale liquefaction device according to claim 1, characterized in that, The export equipment (43) includes one or more of the following: LNG loading arm, Dewar bottle filling gun, and vaporizer.

10. The small-scale liquefaction device according to claim 5, characterized in that, The precooling heat exchanger (31) is a shell-and-tube heat exchanger or a plate-fin heat exchanger; the cryogenic heat exchanger (32) is a plate-fin heat exchanger.

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