CN105627694B - LNG gas stations BOG compresses and liquefies recovery system and method - Google Patents

Abstract

The invention relates to the technical field of whole-station recovery of BOG produced by liquefied natural gas due to heat loss gasification in LNG gas filling stations, specifically a BOG compression liquefaction recovery system and method in LNG gas filling stations, especially including the BOG in the reliquefaction system Optimized design. The adiabatic expander is used to drive the first-stage compressor and the vacuum adiabatic trinity heat exchanger. It has the characteristics of low investment, low operating cost, short process flow, and convenient prying of equipment. It is very suitable for promotion in LNG filling stations.

Description

LNG filling station BOG compression liquefaction recovery system and method

technical field

The invention relates to the technical field of BOG recovery produced in LNG gas filling stations, in particular to a BOG compression liquefaction recovery system for LNG gas filling stations using an expansion compression integrated machine and a vacuum insulation trinity spiral baffle tube heat exchanger, and A method of recovering BOG using the system.

Background technique

With the advent of the "post-oil era", the global energy center is rapidly shifting to more efficient and environmentally friendly natural gas energy. As a national clean energy vehicle, LNG vehicles have developed by leaps and bounds in recent years. At the same time, LNG filling stations have also sprung up like mushrooms after a spring rain. At present, during the operation of LNG filling stations, due to harsh storage conditions and unadvanced design techniques, almost all filling stations are facing serious energy waste, the most prominent of which is the problem of BOG recycling.

During the production and operation of LNG refueling stations, a large amount of BOG gas will be generated due to LNG tanker transportation, storage tank evaporation, unloading, pressure regulation, pre-cooling, pipeline heat absorption, storage tank flashing, and pump operation. BOG gas not only increases the pressure of the gas filling station system, but also brings greater safety hazards. In the end, this part of BOG gas has to be released safely, resulting in huge energy waste and economic losses.

Contents of the invention

This patent aims to provide a BOG optimized compression liquefaction recovery device using an expansion and compression integrated machine and a vacuum insulation trinity spiral baffle tube heat exchanger in an LNG filling station, so as to solve the safety hazards and problems of the current LNG filling station. Environmental pollution and resource waste caused by BOG gas venting.

For realizing above-mentioned technical purpose, the present invention adopts following technical scheme:

The BOG compression liquefaction recovery system of the LNG gas filling station includes an LNG storage tank for storing LNG liquid and a BOG buffer tank for collecting BOG gas in the pipeline of the gas filling station; the LNG storage tank and the BOG buffer tank are connected through the pipeline and vacuum respectively The primary heat exchange area of the adiabatic trinity heat exchanger is connected; the primary heat exchange area of the vacuum adiabatic trinity heat exchanger is connected with the compressor of the adiabatic expansion compression integrated machine, and the compressor of the adiabatic expansion compression integrated machine The secondary compressor is connected to the secondary compressor through the primary air-temperature heat exchanger, and the secondary compressor is connected to the primary heat exchange area of the vacuum insulation trinity heat exchanger through the secondary air-thermal heat exchanger; The three-stage heat exchange area of the vacuum insulation trinity heat exchanger is connected with the adiabatic expander of the adiabatic expansion and compression integrated machine; the adiabatic expander of the adiabatic expansion and compression integrated machine is connected to the gas-liquid separator, and the gas phase of the gas-liquid separator The port is connected to the secondary heat exchange area of the vacuum insulation trinity heat exchanger through a pipeline and a regulating valve, and the liquid phase port of the gas-liquid separator is connected to a cryopump, and the cryopump exchanges heat with the vacuum insulation trinity The tertiary heat exchange area of the device is connected with the LNG storage tank.

As a preference, the vacuum insulation trinity heat exchanger integrates three tubular heat exchangers into one vacuum shell, and spiral baffles are used in the shell to improve heat exchange efficiency, and part of the pipelines are integrated in the shell to make the equipment miniaturized , low investment, simple piping, simplified process. Of course, other forms of three heat exchangers can also be integrated in one vacuum shell, and part of the pipelines are integrated in the shell.

Preferably, the expansion-compression integrated machine utilizes an adiabatic expander to perform refrigeration while driving the compressor to perform one-stage compression on the heat-enriched BOG, which has high refrigeration efficiency, small equipment, low investment, simplified process, and energy saving and consumption reduction.

As a preference, the BOG compression liquefaction recovery system uses DCS to control the BOG recovery compression liquefaction skid, and is respectively linked with the pressure transmitter, temperature transmitter and liquid level transmitter through the regulating valve, which is safe, reliable and easy to operate.

Preferably, the gas phase part of the LNG tanker communicates with the pipeline on the upper part of the BOG buffer tank through pipelines, and check valves are respectively arranged on the pipelines. The BOG compression liquefaction recovery system not only recovers the BOG in the LNG storage tank, but also recovers the BOG gas in the LNG tanker and the pipeline, which prevents energy waste in the gas filling station.

Preferably, the first-stage compressor and the second-stage compressor use a first-stage air-to-air heat exchanger and a second-stage air-to-air heat exchanger to perform interstage condensation, thereby providing cold energy required for liquefaction of BOG gas.

Preferably, the vacuum insulation trinity heat exchanger includes an outer shell and an inner tank, a vacuum shell is formed between the outer shell and the inner tank, and several heat exchange tubes of the vacuum thermal insulation trinity heat exchanger are integrally arranged in the inner tank The first heat exchange area, the second heat exchange area and the third heat exchange area are formed inside, and the tubular heat exchangers in each heat exchange area use spiral baffles to improve heat transfer efficiency.

As a further preference, the tubes between the primary heat exchange area and the secondary heat exchange area, and between the secondary heat exchange area and the tertiary heat exchange area of the vacuum-insulated trinity heat exchanger are respectively connected through tube-side connecting chambers The shell side between the primary heat exchange area and the secondary heat exchange area, and the shell side between the secondary heat exchange area and the tertiary heat exchange area of the vacuum insulation trinity heat exchanger are respectively connected through shell side connecting pipes.

Another object of the present invention is to provide a method for reclaiming BOG using the system described above, comprising the steps of:

S1. Collect the pipeline BOG of the LNG filling station into the buffer tank, and install a regulating valve at the gas phase outlet of the buffer tank. The gas phase of the unloading device is also connected to the compression recovery skid through this regulating valve; the gas phase outlet of the LNG storage tank is installed with a regulating valve It is connected with the compression recovery skid; when the pressure in the storage tank exceeds the specified requirements, the DCS will start the compression recovery skid in chains to recover the BOG gas in the LNG storage tank, and the DCS will stop the compression after the pressure of the LNG storage tank is reduced to the specified value Recovery; when the pressure of the BOG buffer tank reaches a certain value, the DCS will start the compression recovery skid in chains. After the pressure drops to the specified pressure, the compression recovery device will automatically stop; fully recycled. The recovered BOG gas is sent to the vacuum insulated trinity heat exchanger of the liquefaction recovery device for primary heat exchange after the pressure is adjusted separately, so as to fully recover the cold energy of the BOG gas;

S2. In the vacuum adiabatic trinity heat exchanger, the low-temperature BOG gas and the compressed NG at room temperature perform a heat exchange, so that the temperature of the BOG gas rises to about 20°C and becomes NG, and all its cold energy is recovered by the compressed NG gas ;

S3. Then send NG to the first-stage compressor for boosting. The first-stage compressor is driven by the mechanical energy of the adiabatic expansion refrigerator. The adiabatic expander and the first-stage compressor are integrated on one machine base, which not only saves investment but also saves space area, and the cooling efficiency is increased by 70%, and the electricity is saved by 40%. The compressed NG is sent to the second-stage compressor and compressed to 10MPa. The two-stage compression adopts inter-stage condensation to control the temperature of the compressed NG gas at about 30°C, and then sends the compressed NG to the vacuum insulation trinity heat exchanger for further processing. cool down;

S4. The compressed NG performs three-stage heat exchange with the low-temperature recovered BOG, NG after the gas-liquid separator, and part of the LNG in the gas-liquid separator respectively in the vacuum adiabatic trinity heat exchanger, so that the temperature of the compressed NG gas drops to about -110°C; Then the NG is sent to the adiabatic expander, so that the pressure of NG drops to 400KPa, and the temperature of NG drops to about -160°C due to the adiabatic work of NG; most of the NG is liquefied.

S5. Send the gas-liquid mixture into the gas-liquid separator to realize gas-liquid separation; the gaseous low-temperature NG is sent to the vacuum insulation trinity heat exchanger for secondary heat exchange after the pressure is adjusted by the regulating valve, and part of the LNG is pumped to the LNG storage tank. Part of it is sent to the third stage of the vacuum insulation trinity heat exchanger to exchange heat with compressed NG; in the third stage heat exchanger, the temperature of LNG rises to -120°C and is gasified into low temperature NG, and the low temperature NG exiting the third stage heat exchanger passes through the integration The inner shell-side connecting pipe of the heat exchanger and the low-temperature NG of the gas-liquid separator enter the secondary heat exchange of the vacuum adiabatic trinity heat exchanger, and after the heat exchange, enter the primary heat exchanger to cool the compressed NG gas together with the recovered BOG; compression After being cooled in the primary heat exchanger, NG enters the secondary heat exchanger from the interstage tube-side cavity, and enters the tertiary heat exchanger after secondary cooling; the baffle plate in the vacuum insulation trinity heat exchanger is Spiral plate, improve heat exchange efficiency by 30%.

The present invention has at least the following beneficial effects: the mechanical energy generated during adiabatic expansion and refrigeration of low-temperature BOG is used to drive the compressor, and at the same time, one-stage compression is performed on the heat-enriched BOG to reduce energy consumption and improve refrigeration efficiency; it is realized by using a vacuum adiabatic trinity heat exchanger The cold energy of each section of BOG compression refrigeration liquefaction is fully utilized, the heat transfer efficiency is enhanced, and the liquefaction efficiency of BOG recovery is improved; DCS is used to control the BOG recovery compression liquefaction skid, which is safe, reliable, and easy to operate, which is conducive to reducing the safety of LNG filling stations Hidden dangers can be achieved, and BOG gas can be recovered efficiently, thereby avoiding environmental pollution and resource waste caused by BOG gas venting.

Description of drawings

The following drawings are only intended to illustrate and explain the present invention schematically, and do not limit the scope of the present invention. in:

Fig. 1 is the structural representation of the recovery system of the embodiment of the present invention;

Fig. 2 is a structural schematic diagram of a three-stage tubular heat exchanger;

Fig. 3 is a schematic diagram of an enlarged structure at A in Fig. 2;

FIG. 4 is a schematic diagram of an enlarged structure at B in FIG. 2 .

In the figure: 1-LNG storage tank; 11, 21, 81-pipeline; 12, 22, 82-regulating valve; 13, 23, 83-pressure transmitter; 2-BOG buffer tank; 3-vacuum insulation trinity heat exchange 31-first-level heat exchange area; 32-secondary heat exchange area; 33-third-level heat exchange area; 34-outer shell; 35-inner tank; 351-spiral baffle; 36-vacuum shell; Heat pipe; 38-Shell side; 381-Shell side connecting pipe; 39-Tube side; 391-Tube side connection chamber; 4-Adiabatic expansion compressor; 41-Compressor; 42-Adiabatic expander; 5-Level 1 Air-temperature heat exchanger; 6-secondary air-temperature heat exchanger; 7-secondary compressor; 8-gas-liquid separator; 9-cryogenic pump; 10-LNG tanker; 101-pipeline; 24, 102 - Check valve.

detailed description

Below in conjunction with accompanying drawing and embodiment, further elaborate the present invention. In the following detailed description, certain exemplary embodiments of the invention are described by way of illustration only. Needless to say, those skilled in the art would realize that the described embodiments may be modified in various different ways, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are illustrative in nature and not intended to limit the scope of the claims.

As shown in Figures 1 to 4, the BOG compression liquefaction recovery system of the LNG filling station includes an LNG storage tank 1 for storing LNG liquid and a BOG buffer tank 2 for collecting BOG gas in the pipeline of the filling station; the LNG The gas phase part of the storage tank 1 and the BOG buffer tank 2 communicates with the shell side 38 of the primary heat exchange zone 31 of the vacuum insulation trinity heat exchanger 3 through pipelines 11 and 21 respectively; the vacuum insulation trinity heat exchanger 3 The shell side 38 of the primary heat exchange area 31 is connected to the compressor 41 of the adiabatic expansion and compression integrated machine 4, and the compressor 41 of the adiabatic expansion and compression integrated machine 4 is connected to the three The tube side 39 of the first-stage heat exchange zone 31 of the first-stage tube-type vacuum-insulated trinity heat exchanger 3 is connected. The first-stage heat exchange area 31 is connected; the tube side of the third-stage heat exchange area 33 of the vacuum insulation trinity heat exchanger 3 is connected with the adiabatic expander 42 of the expansion-compression integrated machine 4 , and the adiabatic expansion-compression integrated machine 4 The adiabatic expander 42 is connected to the gas-liquid separator 8, and the gas phase port of the gas-liquid separator 8 is connected to the shell side 38 of the secondary heat exchange zone 32 of the vacuum insulation trinity heat exchanger 3 through a pipeline 81, so that The liquid phase port of the gas-liquid separator 8 is connected to the cryopump 9, and the cryopump 9 is connected to the three-stage heat exchange area 33 of the vacuum insulation trinity heat exchanger 3 and the LNG storage tank 1 through a regulating valve and a pipeline Pass.

In order to realize the system DCS control, a regulating valve 22 is installed at the gas phase outlet pipeline 21 of the BOG buffer tank 2, and the gas phase part of the LNG tank car 10 communicates with the pipeline 21 on the top of the BOG buffer tank 2 through the pipeline 101, and the gas phase of the LNG tank car 10 is connected to each other through the pipeline 101. The BOG gas phase port is also connected to the compression liquefaction recovery system (or compression recovery skid) through the regulating valve 22, and the gas phase pipeline 11 on the upper part of the LNG storage tank 1 and the gas phase pipeline 81 on the upper part of the gas-liquid separator 8 are respectively provided with regulating valves 12 , 82, the regulating valves 12, 22, 82 are respectively linked with the temperature transmitter, pressure transmitter 13, 23 and 83 of the compression recovery system. After the pressure in the LNG storage tank 1 and the buffer tank 2 reaches the specified value or the unloading of the LNG tank truck 10 is completed, the DCS will automatically start the compression recovery skid by the control system. BOG gas is recovered. In order to prevent gas from flowing backward, check valves 102 and 24 are provided on the pipeline 101 and the pipeline 21 on the upper part of the BOG buffer tank 2 respectively.

Referring to Fig. 2 to Fig. 4, the vacuum thermal insulation trinity heat exchanger 3 includes an outer shell 34 and an inner tank 35, a vacuum shell 36 is formed between the outer shell 34 and the inner tank 35, and the vacuum thermal insulation trinity heat exchanger Several heat exchange tubes 37 of the device 3 are integrally arranged inside the inner tank 35 to form a primary heat exchange area 31 , a secondary heat exchange area 32 and a tertiary heat exchange area 33 . The tubes 39 between the primary heat exchange area 31 and the secondary heat exchange area 32 and between the secondary heat exchange area 32 and the tertiary heat exchange area 33 of the vacuum insulation trinity heat exchanger 3 are respectively connected by tubes The cavity 391 is connected; the shell side 38 between the primary heat exchange area 31 and the secondary heat exchange area 32 and between the secondary heat exchange area 32 and the tertiary heat exchange area 33 of the vacuum insulation trinity heat exchanger 3 They are respectively communicated through shell-side connecting pipes 381 . In addition, a spiral baffle 351 is disposed in the inner tank 35 of the vacuum insulation trinity heat exchanger 3, which is beneficial to enhance the heat exchange effect of the vacuum insulation trinity heat exchanger.

Please refer to Figure 1 again, the method for recycling BOG using the above-mentioned system includes the following steps:

S1. Collect the BOG gas in the pipeline of the LNG filling station to the BOG buffer tank 2. When the BOG pressure in the BOG buffer tank 2 and LNG storage tank 1 reaches a certain value or after the unloading of the tank truck is completed, the LNG storage tank 1 and the LNG tank The low-temperature recovery BOG in the car 10 and the BOG buffer tank 2 is adjusted to a suitable pressure and flow through the regulating valve, and then sent to the primary heat exchange zone 31 of the vacuum insulation trinity heat exchanger 3 for heat exchange;

S2. In the vacuum adiabatic trinity heat exchanger 3, the low-temperature recovered BOG performs one-stage heat exchange with the normal-temperature compressed NG, so that the temperature of the low-temperature recovered BOG rises to about 20°C to become normal-temperature NG (natural gas), and then the normal-temperature NG is sent to expand One-stage compression boosting is carried out in the compressor 41 of the compression integrated machine 4;

S3. The first-stage compressor 41 of the adiabatic expansion and compression integrated machine 4 relies on the mechanical energy of the adiabatic expander 42 to perform one-stage compression and boosting of normal temperature NG, and uses the first-stage air-temperature heat exchanger 5 to cool the BOG gas to Normal temperature NG, send normal temperature NG to the secondary compressor 7 for secondary compression and pressurization to 10MPa. Cooling in vacuum insulated trinity heat exchanger 3;

S4. The compressed NG performs three-stage heat exchange with the low-temperature recovered BOG, the gas-liquid separator NG and part of the LNG in the gas-liquid separator respectively in the vacuum adiabatic trinity heat exchanger, so that the temperature of the compressed NG drops to about -110°C, and then The NG is sent to the expander 42 of the expansion-compression integrated machine 4, so that the pressure of the NG drops to 400KPa, the temperature of the NG drops to about -160°C, and most of the NG is liquefied into LNG;

S5. The gas-liquid mixture after adiabatic expansion is sent to the gas-liquid separator 8 to realize gas-liquid separation, and the gaseous low-temperature NG is sent to the secondary heat exchange zone 32 of the vacuum adiabatic trinity heat exchanger 3 after the pressure is adjusted by the regulating valve 82. One part of the LNG is pumped to the LNG storage tank 1, and the other part is sent to the third-stage heat exchange zone 33 of the vacuum insulated trinity heat exchanger 3 between the shell side and the second and third stages (that is, the second-stage heat exchange zone and the third-stage heat exchange The second-stage cooling compressed NG from the tube-side connection chamber 391 between the zones) is heat-exchanged, and the temperature rises to -120°C to be gasified. After gasification, the LNG enters the secondary heat-exchange zone through the shell-side connection tube 381 between the second and third stages After 32, enter the secondary heat exchange zone 32 of the three-stage tubular heat exchanger 3 together with the low-temperature NG gas from the gas-liquid separator 8 to cool and compress NG in the shell side, and go out of the secondary heat exchange zone 32 through the first and second stages (i.e. The shell side connecting pipe 381 between the primary heat exchange area and the secondary heat exchange area) enters the shell side 38 of the primary heat exchange area 31 and connects the tube side 39 of the primary heat exchange area 31 together with the low-temperature recovered BOG Compress NG gas for first stage heat exchange.

The invention adopts the mechanical energy generated during the adiabatic expansion and refrigeration of low-temperature BOG to drive the compressor, and at the same time performs one-stage compression on the heat-enriched BOG to reduce energy consumption and improve refrigeration efficiency; a vacuum-insulated trinity spiral baffle tube-and-tube heat exchanger is adopted Realize full use of cold energy in each section of BOG compression refrigeration liquefaction, enhance heat transfer efficiency, and improve liquefaction efficiency of BOG recovery; DCS is used to control BOG compression recovery skids, which is safe, reliable, and easy to operate, which is conducive to reducing the safety of LNG filling stations Hidden dangers can realize efficient recovery of BOG gas, thereby avoiding environmental pollution and resource waste caused by BOG gas venting.

The above descriptions are only illustrative specific implementations of the present invention, and are not intended to limit the scope of the present invention. For example, the three-in-one spiral baffle tube and tube heat exchanger with vacuum insulation can also be realized by adopting three or more stages or other forms of multi-stage heat exchanger structure. The equivalent changes and modifications made shall all belong to the scope of protection of the present invention.

Claims (8)

1. The BOG compression liquefaction recovery system of the LNG gas filling station includes an LNG storage tank (1) for storing LNG liquid and a BOG buffer tank (2) for collecting BOG gas in the pipeline of the gas filling station; it is characterized in that: the LNG storage tank The tank (1) and the BOG buffer tank (2) communicate with the primary heat exchange area (31) of the vacuum insulation trinity heat exchanger (3) through pipelines (11, 21) respectively; the vacuum insulation trinity heat exchange The first-stage heat exchange area (31) of the device (3) is connected with the compressor (41) of the adiabatic expansion-compression integrated machine (4), and the compressor (41) of the adiabatic expansion-compression integrated machine (4) passes through a first-stage The air-temperature heat exchanger (5) is connected with the secondary compressor (7), and the secondary compressor (7) is connected with the vacuum insulation trinity heat exchanger (3) through the secondary air-temperature heat exchanger (6) ) of the first-stage heat exchange area (31) are connected; the third-stage heat exchange area (33) of the vacuum insulation trinity heat exchanger (3) is connected with the adiabatic expansion machine (42) of the adiabatic expansion compression integrated machine (4) pass; the adiabatic expansion machine (42) of the adiabatic expansion and compression integrated machine (4) is connected to the gas-liquid separator (8), and the gas phase port of the gas-liquid separator (8) passes through the pipeline (81) and the regulating valve (82 ) is in communication with the secondary heat exchange area (32) of the vacuum insulation trinity heat exchanger (3), the liquid phase port of the gas-liquid separator (8) is connected to the cryopump (9), and the cryopump ( 9) Communicating with the tertiary heat exchange area (33) of the vacuum insulation trinity heat exchanger (3) and the LNG storage tank (1). 2. The BOG compression liquefaction recovery system of LNG filling station according to claim 1, characterized in that: the vacuum insulation trinity heat exchanger (3) integrates three tubular heat exchangers in a vacuum shell, and the vacuum The shell is provided with a spiral baffle. 3. The BOG compression liquefaction recovery system of LNG filling station according to claim 1, characterized in that: the adiabatic expansion compressor (4) uses an adiabatic expander (42) to drive the compressor (41) while cooling , performing one-stage compression on the heat-enriched BOG. 4. The LNG filling station BOG compression liquefaction recovery system according to claim 1, characterized in that: the pipelines (11, 21, 81) are respectively provided with regulating valves (12, 22, 82), and the regulating valves ( 12, 22, 82) are interlocked with the pressure transmitter, temperature transmitter and liquid level transmitter respectively. 5. The LNG filling station BOG compression liquefaction recovery system as claimed in claim 1, characterized in that: the gas phase part of the LNG tanker (10) passes through the pipeline (101) and the pipeline on the top of the BOG buffer tank (2) ( 21) are connected with each other, and check valves (102, 24) are respectively set on the pipelines (101, 21). 6. The LNG filling station BOG compression liquefaction recovery system according to claim 1, characterized in that: the vacuum insulation trinity heat exchanger (3) comprises a shell (34) and an inner tank (35), and the shell ( 34) and the inner tank (35) to form a vacuum shell (36), and several heat exchange tubes (37) of the vacuum insulation trinity heat exchanger (3) are integrated and arranged inside the inner tank (35) to form the The primary heat exchange area (31), the secondary heat exchange area (32) and the tertiary heat exchange area (33) are described. The tubular heat exchangers in each heat exchange area adopt spiral baffles to improve heat transfer efficiency. 7. The BOG compression liquefaction recovery system of LNG filling station according to claim 6, characterized in that: the primary heat exchange area (31) and the secondary heat exchange area ( 32), the tube side (39) between the secondary heat exchange area (32) and the tertiary heat exchange area (33) are respectively connected through the tube side connecting cavity (391); the vacuum insulation trinity heat exchanger (3) The shell side (38) between the primary heat exchange area (31) and the secondary heat exchange area (32), between the secondary heat exchange area (32) and the tertiary heat exchange area (33) They are connected through the shell-side connecting pipe (381). 8. adopt the method for system recovery BOG as claimed in claim 7, it is characterized in that, comprise the steps: S1. Collect the pipeline BOG of the LNG filling station into the BOG buffer tank, and install a regulating valve at the gas phase outlet of the BOG buffer tank. The gas phase of the LNG tanker is also connected to the compression recovery skid through this regulating valve; the gas phase outlet of the LNG storage tank The regulating valve is installed and connected to the compression recovery skid; when the pressure in the storage tank exceeds the specified requirements, the DCS will start the compression recovery skid in chains to recover the BOG gas in the LNG storage tank, and the DCS will reduce the pressure of the LNG storage tank to the specified value. Compression recovery will be stopped; when the pressure of BOG buffer tank reaches a certain value, DCS will start the compression recovery skid in chains, and after the pressure drops to the specified pressure, the compression recovery device will automatically stop; The NG in the car is fully recovered; the recovered BOG gas is respectively adjusted in pressure and sent to the vacuum insulation trinity heat exchanger of the liquefaction recovery device for primary heat exchange, fully recovering the cold energy of the BOG gas; S2. In the vacuum adiabatic trinity heat exchanger, the low-temperature BOG gas and the compressed NG at room temperature perform a first-stage heat exchange, so that the temperature of the BOG gas rises to 15-25°C and becomes NG, and all its cold energy is converted from the compressed NG gas Recycle; S3. Then send NG to the first-stage compressor to pressurize. The first-stage compressor is driven by the mechanical energy of the adiabatic expansion refrigerator. The compressed NG is sent to the second-stage compressor to compress to 10MPa. The two-stage compression adopts interstage Condensation, so that the temperature of the compressed NG gas is controlled at 25-35°C, and then the compressed NG is sent to the vacuum insulation trinity heat exchanger for cooling; S4. Compressed NG performs three-stage heat exchange with low-temperature recovered BOG, NG after the gas-liquid separator, and part of the LNG in the gas-liquid separator in the vacuum adiabatic trinity heat exchanger, so that the temperature of the compressed NG gas drops to -105 ~ -115 ℃; then send NG into the adiabatic expander to reduce the pressure of NG to 400KPa, and because the temperature of NG adiabatic work drops to -155℃～-165℃, most of the NG is liquefied; S5. Send the gas-liquid mixture into the gas-liquid separator to realize gas-liquid separation; the gaseous low-temperature NG is sent to the vacuum insulation trinity heat exchanger for secondary heat exchange after the pressure is adjusted by the regulating valve, and part of the LNG is pumped to the LNG storage tank. Part of it is sent to the third stage of the vacuum insulation trinity heat exchanger to exchange heat with compressed NG; in the third stage heat exchange area, the LNG temperature rises to -120°C and is gasified into low temperature NG, and the low temperature NG exiting the third stage heat exchange area passes through vacuum insulation The inner shell-side connecting pipe of the trinity heat exchanger and the low-temperature NG of the gas-liquid separator enter the secondary heat exchange of the vacuum adiabatic trinity heat exchanger. After the heat exchange, it enters the primary heat exchange area to cool the compressed NG gas together with the recovered BOG; Compressed NG is cooled from the primary heat exchange area and then enters the secondary heat exchange area from the interstage tube-side cavity, and enters the third heat exchange area from the secondary cooling to enter the cooling.