Liquefied natural gas (LNG) evaporation gas reliquefaction system capable of being cooled and sealed

Abstract

The invention discloses an LNG evaporation gas reliquefaction system capable of being cooled and sealed, and belongs to the technical field of LNG storage and transportation. The reliquefaction system comprises a reliquefaction assembly and a cooling sealing assembly; the reliquefaction assembly comprises a compressor unit, a first cooler, a second cooler, a compression and expansion integrated unit and a heat exchanger. The cooling and sealing assembly comprises a third cooler, a fourth cooler, a fifth cooler, a first stop valve, a flow adjusting valve and a plurality of sealing structures, and the sealing structures are located at the positions, corresponding to the compression end of the compressor unit, the compression end of the compression and expansion integrated unit and the expansion end of the compression and expansion integrated unit, of bearings. And a cooling medium is introduced for cooling and sealing the corresponding bearing. According to the LNG evaporation gas reliquefaction system capable of being cooled and sealed, the positions, corresponding to the bearings, of the compression end and the expansion end can be cooled, and cooling media in the compression end and the expansion end can be prevented from leaking from the bearings.

Description

Technical Field

[0001] The present invention belongs to the technical field of LNG storage and transportation, and particularly relates to a coolable and sealed LNG boil-off gas re-liquefaction system. Background Art

[0002] Marine LNG (Liquefied Natural Gas) transportation does not require laying long transmission pipelines and can flexibly transport natural gas to all parts of the world. Therefore, it has the advantages of flexibility, diverse origins and destinations. During the transportation of any LNG ship, even when the heat insulation performance of the liquid cargo tank is very good, part of the LNG will inevitably evaporate into BOG (boil-off gas). The generation of BOG will cause the pressure in the liquid cargo tank to rise and damage the structure of the liquid cargo tank. If the BOG is directly discharged into the atmosphere, it will also cause direct economic losses and greenhouse hazards.

[0003] Currently, LNG is mainly re-liquefied by a re-liquefaction system that compresses and then expands and cools the refrigeration medium to liquefy the LNG boil-off gas. However, since bearings are provided at the corresponding rotating shafts of the compression end and the expansion end of the re-liquefaction system, during use, the temperature at each bearing is not only high (generated by friction), but also extremely prone to leakage, resulting in failures or performance impacts on the compression end or the expansion end. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement requirements of the prior art, the present invention provides a coolable and sealed LNG boil-off gas re-liquefaction system, aiming to: not only achieve temperature reduction at the corresponding bearings of the compression end and the expansion end, but also inhibit the leakage of the internal cooling medium of the compression end and the expansion end from the bearings. At the same time, it can quickly heat up the cold-end pipeline of the heat exchanger, improve the maintenance efficiency, and eliminate the need for long-term shutdown waiting.

[0005] To achieve the above object, the present invention provides a coolable and sealed LNG boil-off gas re-liquefaction system, which includes a re-liquefaction assembly and a cooling and sealing assembly; The re-liquefaction assembly includes a compressor unit, a first cooler, a second cooler, a compression and expansion integrated unit, and a heat exchanger. The compressor unit is used to compress the refrigeration medium, and the heat exchanger is used for heat exchange between the LNG boil-off gas and the expanded refrigeration medium. The outlet of the compression end of the compressor unit, the hot-end pipeline of the first cooler, the compression end of the compression and expansion integrated unit, the hot-end pipeline of the second cooler, the hot-end pipeline of the heat exchanger, the expansion end of the compression and expansion integrated unit, the cold-end pipeline of the heat exchanger, and the inlet of the compression end of the compressor unit are connected in sequence; The cooling and sealing assembly includes a third cooler, a fourth cooler, a fifth cooler, a first stop valve, a flow regulating valve, and a plurality of sealing structures. Each of the sealing structures is located at the bearing corresponding to the compression end of the compressor unit, the compression end of the compression-expansion integrated unit, or the expansion end of the compression-expansion integrated unit, and is used to introduce a cooling medium to cool and seal the corresponding bearing. The hot end pipeline outlet of the first cooler, the two sealing structures corresponding to the compression-expansion integrated unit, the hot end pipeline of the third cooler, the sealing structure corresponding to the compressor unit, the hot end pipeline of the fourth cooler, and the compression end inlet of the compressor unit are connected in sequence. The compression end outlet of the compressor unit, the first stop valve, the hot end pipeline of the fifth cooler, and the two sealing structures corresponding to the compression-expansion integrated unit are connected in sequence. The hot end pipeline outlet of the heat exchanger, the flow regulating valve, the cold end pipeline of the fifth cooler, and the cold end pipeline inlet of the heat exchanger are connected in sequence.

[0006] Optionally, the compressor unit includes a plurality of compressors arranged in parallel.

[0007] Optionally, the compressor is a two-stage compressor, and the reliquefaction assembly further includes a sixth cooler; The two-stage compressor includes two compression ends. Among them, the outlet of one compression end, the sixth cooler, and the inlet of the other compression end are connected in sequence.

[0008] Optionally, a first branch is connected between the outlet of the first cooler and the outlet of the fourth cooler, and a second stop valve is provided on the first branch.

[0009] Optionally, ultrasonic oscillators are provided at the hot end pipeline outlet of the first cooler, the hot end pipeline outlet of the third cooler, the hot end pipeline outlet of the fifth cooler, the hot end pipeline inlet of the heat exchanger, and the cold end pipeline inlet of the heat exchanger. The ultrasonic oscillators are used to perform ultrasonic vibration on the cooling medium.

[0010] Optionally, temperature sensors are provided on each of the sealing structures; The reliquefaction system further includes a control motor and a controller. The control motor is used to control the opening degree of the flow regulating valve, and the temperature sensor, the controller, and the control motor are electrically connected in sequence.

[0011] Optionally, the temperature of the temperature sensor is 40-80°C.

[0012] Optionally, a rupture disc safety valve is connected to the hot end pipeline outlet of the second cooler.

[0013] Optionally, the cold-end pipelines of the first cooler, the second cooler, the third cooler, and the fourth cooler are all used to introduce seawater, and variable-frequency magnetic field oscillators are provided on the first cooler, the second cooler, the third cooler, and the fourth cooler, and the variable-frequency magnetic field oscillators are used to provide a changing magnetic field to the seawater.

[0014] Optionally, the compression-expansion integrated unit includes a plurality of compression-expansion integrated machines arranged in parallel with each other.

[0015] Optionally, a second branch is connected between the outlet of the second cooler and the inlet of the compression end of the compressor unit, and a branch flow regulating valve is provided on the second branch.

[0016] Optionally, the compression end and the expansion end of the compression-expansion integrated unit are connected by a motor in a transmission manner, and a motor lock module is correspondingly provided on the motor, and the motor lock module is used to inhibit the rotation of the rotating shaft of the motor.

[0017] As long as the above-mentioned improved technical features do not conflict with each other, they can be combined with each other.

[0018] Generally speaking, compared with the prior art, the beneficial effects of the above technical solutions conceived by the present invention include: For a liquefied natural gas (LNG) boil-off gas re-liquefaction system provided by an embodiment of the present invention, a refrigeration medium at normal temperature and pressure (referring to the relative state during the cycle) is compressed by the compression end of a compressor unit to become a cooling medium at high temperature and medium pressure, then cooled by a first cooler to become a cooling medium at normal temperature and medium pressure, then compressed by the compression end of a compression-expansion integrated unit to become a refrigeration medium at high temperature and high pressure, then cooled by a second cooler to become a refrigeration medium at normal temperature and high pressure, and then expanded by the expansion end of the compression-expansion integrated unit to become a cooling medium at low temperature and low pressure. At the same time, in a heat exchanger, heat exchange occurs between the refrigeration medium entering the hot-end pipeline a after being cooled by the second cooler and the refrigeration medium in the cold-end pipeline b; and heat exchange occurs between the LNG boil-off gas and the refrigeration medium in the cold-end pipeline b, so that the LNG boil-off gas is finally re-cooled by the cooling medium at low temperature and low pressure.

[0019] Furthermore, the cooling medium flows sequentially through the outlets of the hot-end pipelines of the first cooler into the two corresponding sealing structures of the compression-expansion integrated unit, the hot-end pipeline of the third cooler, the corresponding sealing structure of the compressor unit, the hot-end pipeline of the fourth cooler, and the compression end inlet of the compressor unit (at this time, the first stop valve and the flow regulating valve are closed). Since the cooling medium is cooled by the first cooler, the temperature of the cooling medium coming out of the first cooler is low (room temperature) and has a certain pressure strength. When it is introduced into the sealing structure (for example, corresponding cavities, flow channels, etc. can be provided in the sealing structure), it can hinder the leakage of the cooling medium inside the bearings at each compression end and expansion end, inhibit the leakage of the cooling medium inside the bearings at the compression end and expansion end, and at the same time cool the bearings, thereby effectively avoiding the problem that the compression end or the expansion end fails or its performance is affected. In addition, after being sealed and cooled, the cooling medium flows back to the compressor unit after being cooled by the third cooler and the fourth cooler to achieve circulation (i.e., normal operating conditions). The third cooler and the fourth cooler can be used to cool the cooling medium for cooling the compression end or the bearing end again in sequence, which can not only ensure that the temperature of the cooling medium finally flowing back to the compression end of the compressor unit is relatively low, but also facilitate the re-compression of the compression end of the compressor unit.

[0020] When the temperature of the bearing at the compression end or the expansion end is too high, the first stop valve is fully opened, and the flow regulating valve is partially opened to provide a small amount of cooling medium at a relatively low temperature (-144°C or so, to avoid fully opening and reducing the refrigeration effect on LNG evaporation gas). These cooling media can exchange heat with the relatively high-temperature cooling medium (about 90°C) coming out of the compressor unit in the fifth cooler, so that the finally emerging cooling medium is cooled down to about 0°C. Its temperature is much lower than the temperature of the cooling medium coming out of the first cooler. At this time, the cooling medium at about 0°C after being cooled by the fifth cooler also flows into the corresponding sealing structure at the compression end or the expansion end for cooling and leakage inhibition. At this time, the cooling effect on the bearing at the compression end or the expansion end is better (i.e., abnormal operating conditions).

[0021] In addition, when the heat exchanger needs to be maintained due to an abnormality (at this time, the temperature of the cold-end pipeline of the heat exchanger is about -°C and direct maintenance cannot be carried out), the flow regulating valve is fully opened at this time (at this time, other structures are operating normally and only the heat exchanger is shut down). As a result, most of the relatively low-temperature cooling medium coming out of the hot-end pipeline of the heat exchanger exchanges heat with the relatively high-temperature cooling medium coming out of the compressor unit, so that the relatively low-temperature cooling medium is heated up and directly flows into the cold-end pipeline of the heat exchanger to quickly heat up the heat exchanger and improve the maintenance efficiency of the heat exchanger.

[0022] That is to say, a cooled and sealed LNG boil-off gas re-liquefaction system provided by an embodiment of the present invention can not only cool the bearings corresponding to the compression end and the expansion end, but also inhibit the leakage of the internal cooling medium at the compression end and the expansion end from the bearings. At the same time, it can quickly heat up the cold-end pipeline of the heat exchanger, improving the maintenance efficiency and eliminating the need for long-term shutdown waiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FIG. is a schematic structural diagram of a cooled and sealed LNG boil-off gas re-liquefaction system provided by an embodiment of the present invention; Figure 2 FIG. is a schematic diagram of the circulation of the cooling medium corresponding to the cooling and sealing assembly of a cooled and sealed LNG boil-off gas re-liquefaction system provided by an embodiment of the present invention under normal operating conditions; Figure 3 FIG. is a schematic diagram of the circulation of the cooling medium corresponding to the cooling and sealing assembly of a cooled and sealed LNG boil-off gas re-liquefaction system provided by an embodiment of the present invention under abnormal operating conditions.

[0024] In all the drawings, the same reference numerals represent the same technical features, specifically: 11. Compressor unit; 111. Compressor; 12. First cooler; 13. Second cooler; 14. Compression-expansion integrated unit; 141. Compression-expansion integrated machine; 15. First heat exchanger; 16. Second heat exchanger; 17. Sixth cooler; 18. Second branch; 19. Branch flow regulating valve; 21. Third cooler; 22. Fourth cooler; 23. Fifth cooler; 24. First stop valve; 25. Flow regulating valve; 26. Sealing structure; 31. First branch; 32. Second stop valve; 33. Ultrasonic oscillator; 34. Bursting disc safety valve; 35. Variable-frequency magnetic field oscillator. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention.

[0027] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0028] In the present invention, unless otherwise clearly specified and limited, terms such as "installed", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] In the present invention, unless otherwise clearly specified and limited, the first feature being "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or simply means that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or simply means that the first feature has a lower horizontal height than the second feature.

[0030] Embodiment

[0031] Figure 1 is a schematic structural diagram of a coolable and sealed LNG boil-off gas re-liquefaction system provided by an embodiment of the present invention. As Figure 1 shown, the re-liquefaction system includes a re-liquefaction component and a cooling and sealing component.

[0032] The re-liquefaction assembly includes a compressor unit 11, a first cooler 12, a second cooler 13, a compression-expansion integrated unit 14 and a heat exchanger. The compressor unit 11 is used to compress the refrigeration medium. The heat exchanger is used to generate heat exchange between the LNG evaporation gas and the expanded refrigeration medium (i.e., the corresponding cold-end pipeline b). The compression-end outlet of the compressor unit 11, the hot-end pipeline of the first cooler 12, the compression end of the compression-expansion integrated unit 14, the hot-end pipeline of the second cooler 13, the hot-end pipeline a of the heat exchanger, the expansion end of the compression-expansion integrated unit 14, the cold-end pipeline b of the heat exchanger and the compression-end inlet of the compressor unit 11 are connected in sequence.

[0033] Among them, the first cooler 12 and the second cooler 13 are used to cool the compressed refrigeration medium; the compression-expansion integrated unit 14 is used to compress the refrigeration medium and expand the cooled refrigeration medium.

[0034] The cooling and sealing assembly includes a third cooler 21, a fourth cooler 22, a fifth cooler 23, a first stop valve 24, a flow regulating valve 25 and a plurality of sealing structures 26. Each sealing structure 26 is located at the bearing corresponding to the compression end of the compressor unit 11, the compression end of the compression-expansion integrated unit 14 or the expansion end of the compression-expansion integrated unit 14, and is used to introduce a cooling medium to cool and seal (i.e., gas seal) the corresponding bearing. The hot-end pipeline outlet of the first cooler 12, the two sealing structures 26 corresponding to the compression-expansion integrated unit 14, the hot-end pipeline of the third cooler 21, the sealing structure 26 corresponding to the compressor unit 11, the hot-end pipeline of the fourth cooler 22 and the compression-end inlet of the compressor unit 11 are connected in sequence. The compression-end outlet of the compressor unit 11, the first stop valve 24, the hot-end pipeline of the fifth cooler 23 and the two sealing structures 26 corresponding to the compression-expansion integrated unit 14 are connected in sequence. The hot-end pipeline a outlet of the heat exchanger, the flow regulating valve 25, the cold-end pipeline of the fifth cooler 23 and the cold-end pipeline b inlet of the heat exchanger are connected in sequence.

[0035] For a LNG evaporation gas re-liquefaction system provided by an embodiment of the present invention, the refrigeration medium at normal temperature and pressure (referring to the relative state during the cycle) is compressed by the compression end of the compressor unit 11 to become a high-temperature medium-pressure cooling medium, and then cooled by the first cooler 12 to become a normal-temperature medium-pressure cooling medium, and then compressed by the compression end ( Figure 1 the left end in the middle) of the compression-expansion integrated unit 14 to become a high-temperature high-pressure refrigeration medium, and then cooled by the second cooler 13 to become a normal-temperature high-pressure refrigeration medium, and then through the expansion end of the compression-expansion integrated unit 14 ( Figure 1The expansion at the right end (middle and right end) becomes a cooling medium with low temperature and low pressure. At the same time, in the heat exchanger, heat exchange occurs between the refrigeration medium that enters the hot end pipeline a after being cooled by the second cooler 13 and the refrigeration medium in the cold end pipeline b; and heat exchange occurs between the LNG evaporation gas and the refrigeration medium in the cold end pipeline b, so that the LNG evaporation gas is finally recooled by the cooling medium with low temperature and low pressure.

[0036] Further, the cooling medium sequentially flows into the two corresponding sealing structures 26 of the compression-expansion integrated unit 14, the hot end pipeline of the third cooler 21, the sealing structure 26 corresponding to the compressor unit 11, the hot end pipeline of the fourth cooler 22, and the compression end inlet of the compressor unit 11 (at this time, the first cut-off valve 24 and the flow regulating valve 25 are closed) through the hot end pipeline outlet of the first cooler 12. Since the cooling medium coming out of the first cooler 12 is cooled, the temperature of the cooling medium coming out of the first cooler 12 is low (room temperature) and has a certain pressure strength. When it is introduced into the sealing structure 26 (for example, corresponding cavities, flow channels, etc. can be set in the sealing structure 26), it can hinder the leakage of the cooling medium inside the bearings of each compression end and expansion end, inhibit the leakage of the cooling medium inside the bearings of the compression end and expansion end, and at the same time cool the bearings, so as to effectively avoid the problems that the compression end or the expansion end fails or its performance is affected. In addition, the cooling medium after sealing and cooling is cooled by the third cooler 21 and the fourth cooler 22 and then flows back to the compressor unit 11 to realize circulation (i.e., normal working condition, see Figure 2 the red line part in). The third cooler 21 and the fourth cooler 22 can be used to cool the cooling medium for cooling the compression end or the bearing end again in sequence, which can not only ensure that the temperature of the cooling medium finally flowing back to the compression end of the compressor unit 11 is relatively low, but also facilitate the re-compression of the compression end of the compressor unit 11.

[0037] When the temperature of the bearing corresponding to the compression end or the expansion end is too high, the first cut-off valve 24 is fully opened, and the flow regulating valve 25 is partially opened to provide a small amount of cooling medium with a lower temperature (-144°C or so, to avoid fully opening and reducing the refrigeration effect on the LNG evaporation gas). These cooling media can exchange heat with the relatively high-temperature cooling medium (about 90°C) coming out of the compressor unit 11 in the fifth cooler 23, so that the finally coming out cooling medium is cooled down to about 0°C. Its temperature is much lower than the temperature of the cooling medium coming out of the first cooler 12. At this time, these cooling media with a temperature of about 0°C after being cooled by the fifth cooler 23 also flow into the corresponding sealing structure 26 of the compression end or the expansion end for cooling and inhibiting leakage. At this time, the cooling effect on the bearing corresponding to the compression end or the expansion end is better (i.e., abnormal working condition, see Figure 3 the yellow line part in).

[0038] In addition, when the heat exchanger needs to be maintained due to an abnormality (at this time, the temperature of the cold-end pipeline of the heat exchanger is about -173°C, and direct maintenance cannot be carried out), the flow regulating valve 25 is fully opened at this time (at this time, other structures are working normally, and only the heat exchanger is shut down). As a result, most of the relatively low-temperature cooling medium coming out of the hot-end pipeline of the heat exchanger exchanges heat with the relatively high-temperature cooling medium coming out of the compressor unit 11, so that the relatively low-temperature cooling medium is heated and then directly flows into the cold-end pipeline of the heat exchanger, rapidly heating the heat exchanger and improving the maintenance efficiency of the heat exchanger.

[0039] That is to say, a coolable and sealed LNG evaporation gas re-liquefaction system provided by an embodiment of the present invention can not only cool the corresponding bearings at the compression end and the expansion end, but also inhibit the leakage of the internal cooling medium at the compression end and the expansion end from the bearings. At the same time, it can rapidly heat the cold-end pipeline of the heat exchanger, improve the maintenance efficiency, and eliminate the need for long-term shutdown waiting.

[0040] In this embodiment, the heat exchanger includes a first heat exchanger 15 and a second heat exchanger 16. Among them, the heat pipe pipelines of the first heat exchanger 15 are respectively connected to the hot-end pipeline outlet of the second cooler 13 and the expansion end inlet of the compression-expansion integrated unit 14, and the cold pipe pipelines of the first heat exchanger 15 are respectively connected to the cold-end pipeline outlet of the second heat exchanger 16 and the compression end inlet of the compressor unit 1; the cold-end pipeline of the second heat exchanger 16 is connected to the expansion end outlet of the compression-expansion integrated unit 14, and the hot-end pipeline of the second heat exchanger 16 is used to introduce LNG evaporation gas.

[0041] Furthermore, the compression end and the expansion end of the compression-expansion integrated unit 14 are drivingly connected by a motor, and a motor lock module is correspondingly arranged on the motor. The motor lock module is used to inhibit the rotation of the rotating shaft of the motor.

[0042] It is easy to understand that the motor lock module inhibits the rotation of the rotating shaft of the motor, thereby inhibiting the rotation of the rotating shaft of the corresponding expansion end of the compression-expansion integrated unit 14 connected to the rotating shaft of the motor, and thus inhibiting the rotation of the impeller of the corresponding expansion end of the compression-expansion integrated unit 14. Correspondingly, when the heat exchanger needs to be maintained due to an abnormality, the motor lock module inhibits the rotation of the impeller of the corresponding expansion end of the compression-expansion integrated unit 14 by inhibiting the rotation of the rotating shaft of the motor. At this time, the flow rate of the cooling medium flowing into the expansion end is small, the expansion cooling of the expansion end is inhibited, and the cooling of the cooling medium is also inhibited. As a result, most of the cooling medium directly flows into the fifth cooler 23 through the flow regulating valve 25 for heating, so that the temperature of the cooling medium finally flowing into the heat exchanger is relatively high and heats the heat exchanger.

[0043] It should be noted that the motor always rotates forward, and only the rotation of the rotating shaft of the motor is inhibited by the motor lock module under abnormal conditions.

[0044] In this embodiment, ultrasonic oscillators 33 are provided at the hot-end pipeline outlet of the first cooler 12, the hot-end pipeline outlet of the third cooler 21, the hot-end pipeline outlet of the fifth cooler 23, the hot-end pipeline inlet of the heat exchanger, and the cold-end pipeline inlet of the heat exchanger. The ultrasonic oscillator 33 is used to perform ultrasonic vibration on the cooling medium.

[0045] It is easy to understand that by performing ultrasonic vibration on the cooling medium through the ultrasonic oscillator 33, the flow of the cooling medium can be disturbed, thereby increasing the heat exchange efficiency of the heat exchanger. For the outlets of the first cooler 12, the third cooler 21, and the fifth cooler 23, by oscillating the cooling medium, the oscillated cooling medium destroys the laminar layer on the surface at the bearing after entering the sealing structure 26, avoiding the laminar layer from hindering heat exchange, thus accelerating the heat exchange at the bearing and achieving a more significant temperature reduction at the bearing.

[0046] Exemplarily, the hot-end pipeline outlet of the first cooler 12 and the hot-end pipeline outlet of the fifth cooler 23 can share one ultrasonic oscillator 33.

[0047] In one implementation manner of the present invention, the compressor unit 11 includes a plurality of compressors 111 arranged in parallel. Additionally, the compression-expansion integrated unit 14 includes a plurality of compression-expansion integrated machines 141 arranged in parallel. Among them, by the plurality of parallel compressors 111 and the plurality of parallel compression-expansion integrated machines 141, the flow rate can be increased, thereby increasing the cooling capacity of the system.

[0048] Further, the compressor 111 is a two-stage compressor, and the re-liquefaction assembly further includes a sixth cooler 17; the two-stage compressor includes two compression ends. Among them, the outlet of one compression end, the sixth cooler 17, and the inlet of the other compression end are connected in sequence.

[0049] In the above embodiment, two-stage compression can be achieved through the two-stage compressor, increasing the compression ratio and raising the pressure of the cooling medium. Additionally, the two-stage compressor has a small volume, avoiding the problem of large volume caused by the parallel arrangement of multiple compressors 111. Correspondingly, the cooling medium flows in from the inlet of the first compression end and finally flows out from the outlet of the other compression end.

[0050] Exemplarily, the two compression ends of the two-stage compressor 111 are synchronously driven by one motor.

[0051] In this embodiment, the first cooler 12 outlet and the fourth cooler 22 outlet are connected through a first branch 31, and a second stop valve 32 is provided on the first branch 31.

[0052] It is easily understandable that the direct connection between the outlet of the first cooler 12 and the outlet of the fourth cooler 22 can be achieved through the first branch 31, enabling the cooler coming out of the first cooler 12 to directly enter the sealing structure 26 corresponding to the compression end of the compressor unit 11 for temperature reduction and leakage suppression. This can not only perform rapid gas replenishment but also improve the cooling efficiency of the bearings corresponding to the compression end of the compressor unit 11.

[0053] In an implementation manner of the present invention, temperature sensors are provided on each sealing structure 26.

[0054] The re-liquefaction system further includes a control motor and a controller (not shown in the figure). The control motor is used to control the opening degree of the flow regulating valve 25, and the temperature sensor, the controller, and the control motor are electrically connected in sequence.

[0055] In the above implementation manner, when the temperature at the bearing corresponding to the compression end or the expansion end is too high, at this time, the first shut-off valve 24 is fully opened, and the temperature of the sealing structure 26 is detected in real time through the temperature sensor. When the temperature sensor detects that the temperature of the sealing structure 26 continues to rise, at this time, the cooling efficiency of the cooling medium for the sealing structure 26 and the bearing is relatively low, and the data detected by the temperature sensor is transmitted to the controller, and the controller controls the control motor to act to increase the opening degree of the flow regulating valve 25. When the temperature sensor detects that the temperature of the sealing structure 26 continues to decrease, at this time, the cooling efficiency of the cooling medium for the sealing structure 26 and the bearing is relatively high, and the data detected by the temperature sensor is transmitted to the controller, and the controller controls the control motor to act to reduce the opening degree of the flow regulating valve 25 to avoid excessive inflow of the cooling medium into the fifth cooler 23 and reducing the refrigeration effect on the LNG evaporation gas. That is to say, by controlling the opening degree of the flow regulating valve 25, the temperature of each sealing structure 26 can be limited within a reasonable range.

[0056] Exemplarily, the temperature of the temperature sensor is 40 - 80 °C, that is, the temperature of the sealing structure 26 and the corresponding bearing is controlled within a suitable range.

[0057] Continue to refer to Figure 1 , a rupture disk safety valve 34 is connected to the hot end pipeline outlet of the second cooler 13 to ensure that the outlet pressure of the second cooler 13 is within a preset range and prevent excessive pressure.

[0058] Moreover, the outlet of the second cooler 13 and the inlet of the compression end of the compressor unit 11 are connected through a second branch 18, and a branch flow regulating valve 19 is provided on the second branch 18.

[0059] In the above implementation manner, under the condition that the branch flow regulating valve 19 is opened, the cooling medium flowing out of the second cooler 13 can directly flow back to the inlet of the compression end of the compressor unit 11, which can not only balance the pressure on the inlet side of the compression end of the compressor unit 11 but also prevent surge.

[0060] In addition, the cold-end pipelines of the first cooler 12, the second cooler 13, the third cooler 21, and the fourth cooler 22 are all used to introduce seawater, so as to cool the cooling medium through seawater, reducing the production cost. The first cooler 12, the second cooler 13, the third cooler 21, and the fourth cooler 22 are provided with variable-frequency magnetic field oscillators 35, and the variable-frequency magnetic field oscillators 35 are used to provide a changing magnetic field to the seawater.

[0061] It is easy to understand that the magnetic field provided by the variable-frequency magnetic field oscillator 35 changes rapidly and periodically. In the changing magnetic field, the metal ions in the seawater generate irregular movements to stir the seawater in the cooler, making the heat exchange efficiency of the corresponding cooler higher.

[0062] Exemplarily, the refrigeration medium can be one or several of He, N2, H2, and Ne.

[0063] A plurality of monitoring modules are provided in this reliquefaction system. Each monitoring module is arranged at the inlet or outlet of the corresponding device. The monitoring module includes a pressure sensor, a pressure display, a temperature sensor, a temperature display, etc., so as to measure or display the pressure or temperature of each pipeline correspondingly, facilitating the monitoring and maintenance of the reliquefaction system.

[0064] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A coolable and sealed LNG boil-off gas re-liquefaction system, characterized in that, The re-liquefaction system includes a re-liquefaction component and a cooling and sealing component; The re-liquefaction component includes a compressor unit, a first cooler, a second cooler, a compression-expansion integrated unit, and a heat exchanger. The compressor unit is used to compress the refrigeration medium. The heat exchanger is used to generate heat exchange between the LNG evaporation gas and the expanded refrigeration medium. The outlet of the compression end of the compressor unit, the hot-end pipeline of the first cooler, the compression end of the compression-expansion integrated unit, the hot-end pipeline of the second cooler, the hot-end pipeline of the heat exchanger, the expansion end of the compression-expansion integrated unit, the cold-end pipeline of the heat exchanger, and the inlet of the compression end of the compressor unit are connected in sequence; The cooling and sealing component includes a third cooler, a fourth cooler, a fifth cooler, a first stop valve, a flow regulating valve, and multiple sealing structures. Each of the sealing structures is located at the bearing corresponding to the compression end of the compressor unit, the compression end of the compression-expansion integrated unit, or the expansion end of the compression-expansion integrated unit, and is used to introduce a cooling medium to cool and seal the corresponding bearing. The outlet of the hot-end pipeline of the first cooler, the two sealing structures corresponding to the compression-expansion integrated unit, the hot-end pipeline of the third cooler, the sealing structure corresponding to the compressor unit, the hot-end pipeline of the fourth cooler, and the inlet of the compression end of the compressor unit are connected in sequence. The outlet of the compression end of the compressor unit, the first stop valve, the hot-end pipeline of the fifth cooler, and the two sealing structures corresponding to the compression-expansion integrated unit are connected in sequence. The outlet of the hot-end pipeline of the heat exchanger, the flow regulating valve, the cold-end pipeline of the fifth cooler, and the inlet of the cold-end pipeline of the heat exchanger are connected in sequence.

2. The re-liquefaction system for boil-off gas of a coolable and sealed LNG according to claim 1, wherein The compressor unit includes multiple compressors arranged in parallel with each other.

3. A coolable and sealed LNG boil-off gas re-liquefaction system according to claim 2, characterized in that, The compressor is a two-stage compressor, and the re-liquefaction component further includes a sixth cooler; The two-stage compressor includes two compression ends. Among them, the outlet of one compression end, the sixth cooler, and the inlet of the other compression end are connected in sequence.

4. A cooled and sealed LNG boil-off gas re-liquefaction system according to claim 1, characterized in that, The outlet of the first cooler and the outlet of the fourth cooler are connected through a first branch, and a second stop valve is provided on the first branch.

5. A coolable and sealed LNG boil-off gas re-liquefaction system according to claim 1, characterized in that, Ultrasonic oscillators are provided at the outlet of the hot-end pipeline of the first cooler, the outlet of the hot-end pipeline of the third cooler, the outlet of the hot-end pipeline of the fifth cooler, the inlet of the hot-end pipeline of the heat exchanger, and the inlet of the cold-end pipeline of the heat exchanger. The ultrasonic oscillator is used to perform ultrasonic vibration on the cooling medium.

6. The re-liquefaction system for boil-off gas of a coolable-sealed LNG according to claim 1, wherein Temperature sensors are provided on each of the sealing structures; The re-liquefaction system further includes a control motor and a controller. The control motor is used to control the opening degree of the flow regulating valve. The temperature sensor, the controller, and the control motor are electrically connected in sequence.

7. A cooled and sealed LNG boil-off gas re-liquefaction system according to claim 6, characterized in that, The temperature of the temperature sensor is 40 - 80 °C.

8. A cooled and sealed LNG boil-off gas re-liquefaction system according to claim 1, characterized in that, A rupture disc safety valve is connected to the outlet of the hot-end pipeline of the second cooler.

9. A cooled and sealed LNG boil-off gas re-liquefaction system according to any one of claims 1-8, characterized in that, The cold end pipelines of the first cooler, the cold end pipelines of the second cooler, the cold end pipelines of the third cooler and the cold end pipelines of the fourth cooler are all used for introducing seawater, and variable frequency magnetic field oscillators are provided on the first cooler, the second cooler, the third cooler and the fourth cooler, and the variable frequency magnetic field oscillators are used to provide a changing magnetic field to the seawater.

10. A coolable and sealed LNG boil-off gas re-liquefaction system according to any one of claims 1-8, characterized in that, The compression-expansion integrated unit includes a plurality of compression-expansion integrated machines arranged in parallel with each other.

11. A coolable and sealable LNG boil-off gas re-liquefaction system according to any one of claims 1-8, characterized in that, A second branch is connected between the outlet of the second cooler and the inlet of the compression end of the compressor unit, and a branch flow regulating valve is provided on the second branch.

12. A coolable and sealed LNG boil-off gas re-liquefaction system according to any one of claims 1-8, characterized in that The compression end and the expansion end of the compression-expansion integrated unit are connected by a motor in a transmission manner, and a motor lock module is correspondingly provided on the motor, and the motor lock module is used to inhibit the rotation of the rotating shaft of the motor.

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