Boil-off gas reliquefaction recovery device and method

Abstract

The invention discloses a boil-off gas reliquefaction recovery device and method, and relates to the technical field of liquefied gas, the boil-off gas reliquefaction recovery device comprises a liquefied gas circulation loop comprising a buffer tank, a circulation pump and a cold box which are sequentially and circularly communicated, and the cold box is internally provided with a refrigeration loop used for providing cold energy; the boil-off gas filling loop is communicated with the buffer tank and is used for filling boil-off gas into the liquefied gas circulation loop; the liquefied gas discharging loop is communicated with the output end of the circulating pump or a downstream channel of the circulating pump and is used for discharging liquefied gas in the liquefied gas circulating loop; according to the evaporation gas reliquefaction recovery device and method, the liquefied gas is subjected to circulating refrigeration, the evaporation gas and the low-temperature liquefied gas are mixed, the evaporation gas is promoted to be cooled and liquefied, then the evaporation gas is recovered along with the original liquefied gas, the diffusion amount of the evaporation gas is reduced, and potential safety hazards, environmental pollution and economic losses caused by diffusion of the evaporation gas are avoided.

Description

Technical Field

[0001] The present invention relates to the field of liquefied gas technology, and more specifically, to a boil-off gas reliquefaction recovery device. Furthermore, the present invention also relates to a recovery method comprising the boil-off gas reliquefaction recovery device. Background Art

[0002] Liquefied natural gas (LNG) is a high-quality energy source widely used in production and daily life due to its clean, efficient, and low-pollution properties. However, since LNG (liquefied natural gas) is a cryogenic liquid at -162 degrees Celsius, boil-off gas (BOG) is generated during LNG production, storage, and transportation. The generation and emission of BOG is not only a hazardous source for production facilities and can cause significant economic losses to businesses, but it also contributes to atmospheric pollution.

[0003] LNG storage tanks are crucial equipment in LNG liquefaction plants, peak-shaving storage and distribution stations, and receiving stations. They are also the primary equipment for generating and temporarily storing boil-off gas (BOG). Boil-off gas is typically pressurized by a compressor before being transported. This pressure-enhanced transport is affected by the operating conditions of the downstream pipeline network. The absence of a pipeline network or insufficient pipeline capacity can limit the recovery and utilization of BOG, leading to its release and ultimately financial losses for the manufacturer.

[0004] In summary, how to solve the potential safety hazards, environmental pollution and economic losses caused by the need to release evaporated gas because it cannot be recycled is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a boil-off gas reliquefaction and recovery device. By circulating refrigeration on the liquefied gas and mixing the boil-off gas with low-temperature liquefied gas, the boil-off gas is cooled and liquefied, and then recovered together with the original liquefied gas, thereby reducing the amount of boil-off gas released and solving the safety hazards, environmental pollution and economic losses caused by the release of boil-off gas.

[0006] Another object of the present invention is to provide a recovery method including the above-mentioned boil-off gas reliquefaction recovery device, in which the boil-off gas is cooled and liquefied by circulating low-temperature liquefied gas, so that the liquefied liquefied gas and the original low-temperature liquefied gas are recovered simultaneously, thereby reducing the release of boil-off gas.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A boil-off gas reliquefaction recovery device, comprising:

[0009] A liquefied gas circulation loop comprises a buffer tank, a circulation pump and a cold box which are circulated in sequence, wherein a refrigeration circuit for providing cold energy is provided in the cold box;

[0010] a boil-off gas filling circuit, which is in communication with the buffer tank and is used to fill boil-off gas into the liquefied gas circulation circuit;

[0011] The liquefied gas discharge circuit is connected to the output end of the circulation pump or the channel downstream thereof, and is used to discharge the liquefied gas in the liquefied gas circulation circuit.

[0012] Preferably, a pre-cooling circuit is further included, which is connected to the input end of the buffer tank or the channel upstream thereof, and is used to add low-temperature liquefied gas to the buffer tank.

[0013] Preferably, the pre-cooling circuit includes a first branch circuit and a second branch circuit;

[0014] The first branch circuit is connected to the input end of the upper layer of the buffer tank and is used to add cryogenic liquefied gas from the upper part of the buffer tank;

[0015] The second branch circuit is connected to the input end of the lower layer of the buffer tank and is used for filling the low-temperature liquefied gas from the lower part of the buffer tank.

[0016] Preferably, a spray mechanism is provided in the buffer tank, and the spray mechanism is connected to the output end of the cold box and is used to spray the liquefied gas refrigerated by the cold box;

[0017] The output end of the evaporative gas filling circuit overlaps with at least a portion of the spraying area of the spray mechanism.

[0018] Preferably, the input end of the liquefied gas discharge circuit is connected to the liquefied gas circulation circuit downstream of the circulation pump through a three-way joint;

[0019] A control valve is provided at the output end of the three-way joint or in the passage between the three-way joint and the liquefied gas discharge circuit and / or the buffer tank, for controlling the fluid flow distribution from the three-way joint to the liquefied gas discharge circuit and the buffer tank.

[0020] Preferably, the control valve is a liquid level control valve;

[0021] A liquid level sensor is provided in the buffer tank, and an output end of the liquid level sensor is electrically connected to the control unit of the liquid level control valve.

[0022] Preferably, it further comprises a bypass circuit, wherein the bypass circuit is connected in parallel with the cold box;

[0023] The bypass circuit and the liquefied gas circulation circuit are both provided with control valves for controlling the connection between the bypass circuit and the cold box.

[0024] Preferably, it further comprises an evaporation gas supply circuit, wherein the output end of the evaporation gas supply circuit is connected to the buffer tank and / or the evaporation gas filling circuit, and is used for filling the buffer tank with evaporation gas;

[0025] A pressure control valve is provided in the passage of the evaporated gas supply circuit;

[0026] A first pressure sensor is provided in the buffer tank, and an output end of the first pressure sensor is electrically connected to the control unit of the pressure control valve.

[0027] Preferably, it further comprises an overpressure relief circuit, wherein the input end of the overpressure relief circuit is connected to the buffer tank via a first safety valve.

[0028] Preferably, the input and output ends of the cold box are respectively provided with second temperature sensors for detecting the temperature of the fluid entering and flowing out of the cold box, and the output end of the second temperature sensor is electrically connected to the control unit of the refrigeration circuit.

[0029] A recovery method, applied to any of the above-mentioned boil-off gas reliquefaction recovery devices, comprising:

[0030] Controlling the circulation pump to operate and drive the liquefied gas to circulate in the liquefied gas circulation loop;

[0031] Controlling the operation of the cold box to cool the liquefied gas in the liquefied gas circulation loop;

[0032] When the pressure in the buffer tank is less than a preset value, controlling the boil-off gas filling circuit to fill boil-off gas into the buffer tank;

[0033] When the liquid level in the buffer tank is greater than a preset value, the liquefied gas discharge circuit is controlled to discharge the liquefied gas in the liquefied gas circulation circuit.

[0034] The boil-off gas reliquefaction recovery device provided by the present invention has at least the following beneficial effects compared with the prior art:

[0035] The liquefied gas is continuously circulated in the liquefied gas circulation loop by the action of the circulation pump. During the circulation process, the liquefied gas is continuously cooled by the action of the cold box, so that the evaporated gas newly entering the liquefied gas circulation loop can be mixed with the original low-temperature liquefied gas, cooled and liquefied, and then recovered together with the original low-temperature liquefied gas. No new substances are introduced in the whole process, and the impurity content of the liquefied gas will not change.

[0036] The cold is stored and transported through liquid liquefied gas, and then the low-temperature liquefied gas is combined with the evaporation gas to cool and liquefy the evaporation gas. Compared with directly cooling the evaporation gas, it has a higher cold storage efficiency, thereby improving the liquefaction recovery efficiency of the evaporation gas.

[0037] The recovery method provided by the present invention is applied to the above-mentioned boil-off gas reliquefaction recovery device and has the same effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0039] Figure 1 This is a schematic structural diagram of a specific embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the flow of refrigerant in the refrigeration circuit in the first specific embodiment provided by the present invention;

[0041] Figure 3 This is a structural diagram of the second specific embodiment provided by the present invention.

[0042] In the picture:

[0043] 1. Buffer tank; 11. First temperature sensor; 12. Liquid level sensor; 13. Spray mechanism; 14. First pressure sensor; 15. Pneumatic control valve; 16. First safety valve;

[0044] 2. Circulation pump;

[0045] 3. Cold box; 31. Refrigeration circuit; 311. Compressor / expander; 312. Refrigerant cooler; 313. Refrigerant replenishing circuit; 314. Second safety valve; 32. Second pressure sensor; 33. Second temperature sensor; 34. Third safety valve;

[0046] 4. Evaporative gas filling circuit;

[0047] 5. Liquefied gas discharge circuit; 51. First liquid level control valve; 52. Second liquid level control valve;

[0048] 6. Pre-cooling circuit; 61. First branch circuit; 62. Second branch circuit;

[0049] 7. Evaporative gas supply circuit; 71. Pressure control valve; 72. Check valve;

[0050] 8. Overpressure relief circuit;

[0051] 9. Bypass circuit.

[0052] Figure 1The solid arrows in the middle are the flow direction of liquefied gas, and the hollow arrows are the flow direction of evaporated gas;

[0053] Figure 2 The solid arrow in the middle indicates the flow direction of the low-temperature refrigerant, and the hollow arrow indicates the flow direction of the high-temperature refrigerant. DETAILED DESCRIPTION

[0054] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0055] The core of the present invention is to provide a boil-off gas reliquefaction and recovery device. By circulating refrigeration on the liquefied gas and mixing the boil-off gas with low-temperature liquefied gas, the boil-off gas is cooled and liquefied, and then recovered together with the original liquefied gas, thereby reducing the amount of boil-off gas released and solving the safety hazards, environmental pollution and economic losses caused by the release of boil-off gas.

[0056] Another core of the present invention is to provide a recovery method including the above-mentioned boil-off gas reliquefaction recovery device, in which the boil-off gas is cooled and liquefied by low-temperature circulating liquefied gas, so that the liquefied liquefied gas and the original low-temperature liquefied gas are recovered synchronously, thereby reducing the release of boil-off gas.

[0057] Please refer to Figure 1 、 Figure 2 and Figure 3 , a boil-off gas reliquefaction recovery device, comprising:

[0058] The liquefied gas circulation circuit includes a buffer tank 1, a circulation pump 2 and a cold box 3 which are circulated in sequence. The cold box 3 is provided with a refrigeration circuit 31 for providing cold energy.

[0059] Boil-off gas filling circuit 4, which is connected to the buffer tank 1 and is used to add boil-off gas to the liquefied gas circulation circuit;

[0060] The liquefied gas discharge circuit 5 is connected to the output end of the circulation pump 2 or a channel downstream thereof, and is used to discharge the liquefied gas in the liquefied gas circulation circuit.

[0061] like Figure 1 As shown, the buffer tank 1 is pre-filled with liquefied gas, and the circulating pump 2 drives the liquefied gas to circulate continuously in the embossing machine circulation loop. During the process, the refrigeration circuit 31 in the cold box 3 can continuously provide cold capacity, continuously refrigerate the circulating liquefied gas, and form low-temperature liquefied gas;

[0062] Boil-off gas is added to the buffer tank 1 through the boil-off gas filling circuit 4. After the boil-off gas combines with the low-temperature liquefied gas in the buffer tank 1, it absorbs the cold energy in the low-temperature liquefied gas, thereby cooling and liquefying the boil-off gas.

[0063] When the liquid level in the buffer tank 1 reaches the preset value, the liquefied gas after the evaporation gas is liquefied can be discharged together with the original liquefied gas to complete the liquefaction recovery of the evaporation gas;

[0064] Furthermore, the entire liquefaction process can be carried out continuously, that is, the evaporation gas can be continuously liquefied and recovered, thereby significantly improving the recovery efficiency of the evaporation gas.

[0065] Moreover, in the cold box 3, liquid liquefied gas is used as the refrigeration object, and its own density is significantly greater than that of the gaseous evaporated gas. Therefore, the energy required for its circulation and the volume required for the cooling equipment are significantly smaller than those of the evaporated gas. Therefore, low-temperature liquefied gas with a lower temperature can be obtained within less power consumption, which helps it to combine with more evaporated gas, so that more evaporated gas can be cooled and liquefied, that is, the liquefaction efficiency of the evaporated gas is improved.

[0066] In some embodiments, such as Figure 1 As shown, the input end of the liquefied gas discharge circuit 5 is connected to the passage between the cold box 3 and the buffer tank 1. That is, when the liquid level in the buffer tank 1 reaches a preset value, the liquefied gas is cooled by the cold box 3 and then enters the liquefied gas discharge circuit 5 for discharge. That is, the discharged gas is the low-temperature liquefied gas refrigerated by the cold box 3, which helps to further reduce the temperature of the liquefied gas and prevent it from gasifying into evaporated gas during or after the discharge.

[0067] In some embodiments, such as Figure 3 As shown, the input end of the liquefied gas discharge circuit 5 is connected to the path between the circulation pump 2 and the cold box 3. That is, when the liquid level in the buffer tank 1 reaches a preset value, the liquefied gas is directly discharged into the liquefied gas discharge circuit 5 under the pressure of the circulation pump 2. That is, the discharged liquefied gas does not pass through the cold box 3 for re-refrigeration, which can significantly reduce the discharge flow resistance, reduce the load on the circulation pump 2, and reduce the energy consumption of the equipment. This embodiment can also be used to recover the liquefied gas in the buffer tank 1 when the liquefied gas circulation is not in progress.

[0068] In some embodiments, a pneumatic control valve 15 is provided at the output end of the buffer tank 1 or in the passage between the buffer tank 1 and the circulation pump 2 to control the on-off of the output end of the buffer tank 1 or the passage between the buffer tank 1 and the circulation pump 2. Pneumatic control is adopted, and there is no electric spark, which helps to ensure production safety.

[0069] In some embodiments, a filter is further provided in the liquefied gas circulation loop to filter the circulating liquefied gas to ensure smooth flow of the liquefied gas circulation loop.

[0070] In some embodiments, a pre-cooling circuit 6 is further included. The pre-cooling circuit 6 is connected to the input end of the buffer tank 1 or the channel upstream thereof, and is used to add low-temperature liquefied gas to the buffer tank 1.

[0071] like Figure 1 As shown, the input end of the pre-cooling circuit 6 is connected to the LNG storage tank, and the low-temperature liquefied gas in the LNG storage tank is pre-filled into the buffer tank 1. When the low-temperature liquefied gas enters the buffer tank 1, it can be vaporized due to pressure changes, absorb the heat in the buffer tank 1, and quickly reduce the internal temperature of the buffer tank 1, thereby avoiding the liquefied gas after refrigeration by the cold box 3 from being vaporized due to high temperature when it enters the buffer tank 1 again.

[0072] In some embodiments, the pre-cooling circuit 6 includes a first branch circuit 61 and a second branch circuit 62;

[0073] The first branch circuit 61 is connected to the input end of the upper layer of the buffer tank 1 and is used to add cryogenic liquefied gas from the upper part of the buffer tank 1;

[0074] The second branch circuit 62 is connected to the input end of the lower layer of the buffer tank 1 and is used for filling the low-temperature liquefied gas from the lower part of the buffer tank 1 .

[0075] like Figure 1 As shown, the pre-cooling circuit 6 adopts a branching method, which is respectively connected to the upper filling port and the lower filling port of the buffer tank 1, and both are filled with low-temperature liquefied gas. The liquefied gas filled at the upper filling port can quickly vaporize and absorb heat when it descends, and quickly absorb the heat of the upper layer of the buffer tank 1, thereby reducing the temperature in the buffer tank 1. When the temperature of the buffer tank 1 drops to a certain level, liquefied gas is added through the lower filling port, which accelerates the cooling of the lower part of the buffer tank 1 and gathers liquefied gas at the bottom of the buffer tank 1, thereby ensuring that the liquefied gas circulating in the circulation pump 2 is in liquid state, thereby avoiding damage to the circulation pump 2.

[0076] In some embodiments, shut-off valves are provided at the first branch circuit 61, the second branch circuit 62 and / or the upper and lower filling ports of the buffer tank 1 to control the on and off of the pre-cooling circuit 6. During operation, the first temperature sensor 11 arranged at the upper and lower parts of the buffer tank 1 is used to detect the temperatures of the upper and lower parts of the buffer tank 1 to control the pre-cooling speed of the buffer tank 1. When the temperature at the corresponding position reaches the preset temperature, the corresponding branch circuit is closed.

[0077] In some embodiments, a spray mechanism 13 is provided in the buffer tank 1 , and the spray mechanism 13 is connected to the output end of the cold box 3 for spraying the liquefied gas refrigerated by the cold box 3 ;

[0078] The output end of the evaporative gas filling circuit 4 overlaps with at least a portion of the spraying area of the spraying mechanism 13 .

[0079] like Figure 1As shown, the low-temperature liquefied gas cooled by the cold box 3 is sprayed by the spray mechanism 13 when entering the buffer tank 1, and is fully contacted with the newly added boil-off gas, thereby improving the cold exchange efficiency between the boil-off gas and the liquefied gas and promoting the rapid liquefaction of the boil-off gas;

[0080] In some embodiments, the spray mechanism 13 is arranged at an upper position in the buffer tank 1 , that is, the sprayed low-temperature liquefied gas can fully contact the boil-off gas in the upper layer of the buffer tank 1 to accelerate the liquefaction of the boil-off gas in the buffer tank 1 .

[0081] In some embodiments, the input end of the liquefied gas discharge circuit 5 is connected to the liquefied gas circulation circuit downstream of the circulation pump 2 through a three-way connector;

[0082] A control valve is provided at the output end of the tee or in the passage between it and the liquefied gas discharge circuit 5 and / or the buffer tank 1 to control the fluid flow distribution from the tee to the liquefied gas discharge circuit 5 and the buffer tank 1 .

[0083] like Figure 1 As shown, when the liquid level in the buffer tank 1 reaches a preset value, the liquefied gas in the buffer tank 1 needs to be discharged. At this time, the flux of the three-way joint connecting the liquefied gas discharge circuit 5 and the channel entering the buffer tank 1 is adjusted by the control valve to change the ratio of the liquefied gas discharged and entering the buffer tank 1 after circulating through the liquefied gas circulation circuit.

[0084] The control valve is preferably a regulating valve, which is convenient for adjusting the flux of each channel.

[0085] In some embodiments, the control valve is a level control valve;

[0086] A liquid level sensor 12 is provided in the buffer tank 1 , and an output end of the liquid level sensor 12 is electrically connected to a control unit of the liquid level control valve.

[0087] like Figure 1 As shown, a first liquid level control valve 51 is provided between the three-way joint and the liquefied gas discharge circuit 5, and a second liquid level control valve 52 is provided between the three-way joint and the buffer tank 1; the liquid level in the buffer tank 1 is detected by the liquid level sensor 12;

[0088] When the liquid level is lower than the preset range, the first liquid level control valve 51 is closed, and the liquefied gas circulates only in the liquefied gas circulation loop;

[0089] When the liquid level is higher than the preset range, the first liquid level control valve 51 opens and appropriately reduces the flow of the second liquid level control valve 52, so that a large amount of liquefied gas enters the liquefied gas discharge circuit 5 and is then discharged, such as to an external liquefied gas storage tank for storage;

[0090] When the liquid level is within the preset range, the first liquid level control valve 51 and the second liquid level control valve 52 are regulated according to the set flux ratio, so that the liquefied gas entering the liquefied gas discharge circuit 5 and the liquefied gas entering the buffer tank 1 are proportional, ensuring that part of the liquefied gas can be discharged and a sufficient amount of liquefied gas is retained to continue circulating in the liquefied gas circulation circuit.

[0091] In some embodiments, a bypass circuit 9 is further included, and the bypass circuit 9 is connected in parallel with the cold box 3;

[0092] Control valves are provided in both the bypass circuit 9 and the liquefied gas circulation circuit for controlling whether the bypass circuit 9 or the cold box 3 is connected.

[0093] When the equipment or the cold box 3 is under maintenance, the liquefied gas in the pipeline needs to be recovered to the buffer tank 1 or the external liquefied gas storage tank. At this time, the cold box 3 is closed so that the liquefied gas can be recovered to the buffer tank 1 or the external liquefied gas storage tank through the bypass circuit 9.

[0094] Alternatively, in the initial stage of equipment startup, in order to reduce the startup load of the circulation pump 2, the bypass loop 9 can also be used to short-circuit the cold box 3, so that the liquefied gas circulates only in the buffer tank 1 and the bypass loop 9.

[0095] In some embodiments, an evaporation gas supply circuit 7 is further included, and an output end of the evaporation gas supply circuit 7 is connected to the buffer tank 1 and / or the evaporation gas filling circuit 4 for filling the buffer tank 1 with evaporation gas;

[0096] A pressure control valve 71 is provided in the passage of the evaporated gas supply circuit 7;

[0097] A first pressure sensor 14 is provided in the buffer tank 1 , and an output end of the first pressure sensor 14 is electrically connected to a control unit of the pressure control valve 71 .

[0098] When the evaporation gas filling circuit 4 has not been filled with evaporation gas for a long time, the pressure in the buffer tank 1 may drop due to the complete liquefaction of the evaporation gas, and there is a risk that the buffer tank 1 may be crushed. Therefore, the evaporation gas replenishment circuit 7 is used to appropriately replenish the evaporation gas in the buffer tank 1 to ensure that the pressure in the buffer tank 1 is stable.

[0099] In some embodiments, a pressure control valve 71 is provided in the evaporated gas supply circuit 7 and is linked to the first pressure sensor 14 in the buffer tank 1. When the pressure in the buffer tank 1 is lower than a preset value, the evaporated gas supply circuit 7 can be automatically opened to replenish evaporated gas into the buffer tank 1.

[0100] In actual use, a check valve 72 is provided in the evaporated gas supply circuit 7 to prevent the evaporated gas from flowing in the reverse direction.

[0101] In some embodiments, an overpressure relief circuit 8 is further included, and an input end of the overpressure relief circuit 8 is connected to the buffer tank 1 through a first safety valve 16 .

[0102] By providing the first safety valve 16 , when the pressure in the buffer tank 1 exceeds the safety pressure value, the pressure is released through the first safety valve 16 , allowing the evaporated gas to enter the external processing device through the overpressure relief circuit 8 , thereby ensuring the pressure in the buffer tank 1 is stable.

[0103] In some embodiments, a third safety valve 34 is provided in the pipeline of the liquefied gas circulation loop to ensure that the pressure in the liquefied gas circulation loop does not exceed a safe value.

[0104] In some embodiments, the input and output ends of the cold box 3 are respectively provided with second temperature sensors 33 for detecting the temperature of the fluid entering and flowing out of the cold box 3, and the output end of the second temperature sensor 33 is electrically connected to the control unit of the refrigeration circuit 31.

[0105] like Figure 1 As shown, a second pressure sensor 32 and a second temperature sensor 33 are provided upstream and downstream of the cold box 3 to detect the temperature and pressure upstream and the temperature and pressure downstream of the cold box 3, thereby evaluating the total amount of cold absorbed by the liquefied gas when passing through the cold box 3, and then regulating the refrigeration circuit 31.

[0106] Among them, the refrigeration circuit 31 includes a mechanical refrigeration cycle loop composed of a compression expander 311, a refrigerant cooler 312 and a cold box 3, and heat is transported by the internally circulating refrigerant to achieve refrigeration in the cold box 3, wherein the cold box 3 includes a supercooling section and a low-temperature section, wherein the liquefied gas exchanges cold with the refrigerant in the supercooling section, and the refrigerant that releases supercooling after passing through the supercooling section enters the low-temperature section again, and exchanges cold with the high-pressure refrigerant that has not been expanded by the compression expander 311, thereby reducing the cold capacity of the high-pressure refrigerant, so that the high-pressure refrigerant can obtain a lower temperature after expanding through the compression expander 311.

[0107] In some embodiments, a second safety valve 314 is provided in the mechanical refrigeration cycle to ensure that the pressure in the mechanical refrigeration cycle does not exceed the safety pressure value, thereby ensuring the stable circulation of the refrigerant; at the same time, a refrigerant replenishing circuit 313 is connected to the mechanical refrigeration cycle to ensure sufficient refrigerant in the mechanical refrigeration cycle.

[0108] In addition to the boil-off gas reliquefaction recovery devices disclosed in the above embodiments, the present invention further provides a recovery method applied to the above boil-off gas reliquefaction recovery devices, which is applied to any of the above boil-off gas reliquefaction recovery devices and comprises:

[0109] Control the circulation pump 2 to operate and drive the liquefied gas to circulate in the liquefied gas circulation loop;

[0110] Control the operation of the cold box 3 to cool the liquefied gas in the liquefied gas circulation loop;

[0111] When the pressure in the buffer tank 1 is lower than the preset value, the boil-off gas filling circuit 4 is controlled to fill boil-off gas into the buffer tank 1;

[0112] When the liquid level in the buffer tank 1 is greater than a preset value, the liquefied gas discharge circuit 5 is controlled to discharge the liquefied gas in the liquefied gas circulation circuit.

[0113] During operation, the pre-cooling circuit 6 is controlled to first fill the buffer tank 1 with low-temperature liquefied gas, so that the temperature in the buffer tank 1 is reduced to a preset temperature, and the buffer tank 1 temporarily stores some liquid liquefied gas;

[0114] The circulation pump 2 and the cold box 3 are controlled to start, and the liquefied gas is promoted to circulate and cool down in the liquefied gas circulation loop. When the pressure in the buffer tank 1 is lower than the preset pressure, the evaporative gas is continuously added to the buffer tank 1 through the evaporative gas filling circuit 4. The evaporative gas contacts the refrigerated liquefied gas, absorbs the coldness in the liquefied gas, and is liquefied, and circulates and refrigerates together with the original liquefied gas; until the liquid level in the buffer tank 1 is greater than the preset value, the liquefied gas discharge circuit 5 is controlled to be connected, and the liquefied liquefied gas is discharged, completing the liquefaction recovery of the evaporative gas.

[0115] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0116] The above describes in detail the boil-off gas reliquefaction and recovery apparatus and method provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above examples is intended only to facilitate understanding of the method and core concepts of the present invention. It should be noted that those skilled in the art may make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications fall within the scope of protection of the claims.

Claims

1. A boil-off gas reliquefaction recovery device, characterized in that: include: A liquefied gas circulation loop comprises a buffer tank (1), a circulation pump (2), and a cold box (3) which are circulated and conducted in sequence, wherein a refrigeration circuit (31) for providing cold energy is provided in the cold box (3); a boil-off gas filling circuit (4), which is in communication with the buffer tank (1) and is used to fill boil-off gas into the liquefied gas circulation circuit; A liquefied gas discharge circuit (5) is connected to the output end of the circulation pump (2) or a channel downstream thereof, and is used to discharge the liquefied gas in the liquefied gas circulation circuit.

2. The boil-off gas reliquefaction recovery device according to claim 1, characterized in that: It also includes a pre-cooling circuit (6), which is connected to the input end of the buffer tank (1) or a channel upstream thereof, and is used to fill the buffer tank (1) with low-temperature liquefied gas.

3. The boil-off gas reliquefaction recovery device according to claim 2, characterized in that: The pre-cooling circuit (6) comprises a first branch circuit (61) and a second branch circuit (62); The first branch circuit (61) is connected to the input end of the upper layer of the buffer tank (1) and is used for filling the low-temperature liquefied gas from the upper part of the buffer tank (1); The second branch circuit (62) is connected to the input end of the lower layer of the buffer tank (1); Used for filling low-temperature liquefied gas from the lower part of the buffer tank (1).

4. The boil-off gas reliquefaction recovery device according to claim 1, characterized in that: A spray mechanism (13) is provided in the buffer tank (1), and the spray mechanism (13) is connected to the output end of the cold box (3) and is used to spray the liquefied gas refrigerated by the cold box (3); The output end of the evaporative gas filling circuit (4) overlaps with at least a portion of the spraying area of the spraying mechanism (13).

5. The boil-off gas reliquefaction recovery device according to claim 1, characterized in that: The input end of the liquefied gas discharge circuit (5) is connected to the liquefied gas circulation circuit downstream of the circulation pump (2) via a three-way joint; A control valve is provided at the output end of the three-way joint or in the passage between the three-way joint and the liquefied gas discharge circuit (5) and / or the buffer tank (1), for controlling the distribution of fluid flow from the three-way joint to the liquefied gas discharge circuit (5) and the buffer tank (1).

6. The boil-off gas reliquefaction recovery device according to claim 5, characterized in that: The control valve is a liquid level control valve; A liquid level sensor (12) is provided in the buffer tank (1), and an output end of the liquid level sensor (12) is electrically connected to a control unit of the liquid level control valve.

7. The boil-off gas reliquefaction recovery device according to claim 1, characterized in that: It also includes a bypass circuit (9), wherein the bypass circuit (9) is connected in parallel with the cold box (3); Control valves are provided in both the bypass circuit (9) and the liquefied gas circulation circuit, for controlling the bypass circuit (9) and the cold box (3) to be selectively connected.

8. The boil-off gas reliquefaction recovery device according to claim 1, characterized in that: It also includes an evaporation gas supply circuit (7), the output end of the evaporation gas supply circuit (7) being connected to the buffer tank (1) and / or the evaporation gas filling circuit (4) for filling the buffer tank (1) with evaporation gas; A pressure control valve (71) is provided in the passage of the evaporated gas supply circuit (7); A first pressure sensor (14) is provided in the buffer tank (1), and an output end of the first pressure sensor (14) is electrically connected to a control unit of the pressure control valve (71).

9. The boil-off gas reliquefaction recovery device according to claim 1, characterized in that: It also includes an overpressure relief circuit (8), the input end of the overpressure relief circuit (8) being connected to the buffer tank (1) via a first safety valve (16).

10. The boil-off gas reliquefaction recovery device according to claim 1, characterized in that: The input end and output end of the cold box (3) are respectively provided with a second temperature sensor (33) for detecting the temperature of the fluid entering and flowing out of the cold box (3), and the output end of the second temperature sensor (33) is electrically connected to the control unit of the refrigeration circuit (31).

11. A recycling method, characterized in that: The boil-off gas reliquefaction recovery device according to any one of claims 1 to 10 comprises: Controlling the circulation pump (2) to operate and drive the liquefied gas to circulate in the liquefied gas circulation loop; Controlling the operation of the cold box (3) to cool the liquefied gas in the liquefied gas circulation loop; When the pressure in the buffer tank (1) is less than a preset value, controlling the evaporated gas filling circuit (4) to fill the buffer tank (1) with evaporated gas; When the liquid level in the buffer tank (1) is greater than a preset value, the liquefied gas discharge circuit (5) is controlled to discharge the liquefied gas in the liquefied gas circulation circuit.

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