BOG treatment equipment for LNG receiving station and BOG treatment process of BOG treatment equipment

Abstract

The invention provides BOG treatment equipment for an LNG receiving station and a BOG treatment process of the BOG treatment equipment, and relates to the technical field of BOG treatment of the LNG receiving station. A first compressor and a second compressor are arranged in parallel, and BOG conveyed out of the LNG receiving station can enter the first compressor or the second compressor; bOG can enter the first compressor or the second compressor selectively according to the load condition, the BOG compressed by the compressor enters the cooler, the BOG cooled by the cooler enters the immersed recondenser, in-station condensation recovery is achieved, LNG in the immersed recondenser is pressurized and enters the cooler, and the LNG in the immersed recondenser enters the cooler. The BOG from the outlet of the compressor in the cooler exchanges cold with the high-pressure LNG from the immersed recondenser, deep recovery of the BOG is realized by fully utilizing a cold source in the station, and the technical effect of recovering the BOG in an energy-saving and consumption-reducing manner is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of BOG treatment in LNG receiving stations, and in particular to a BOG treatment device and a BOG treatment process for LNG receiving stations. Background Art

[0002] LNG (Liquefied Natural Gas) is a clean energy source that has been widely used globally in recent years. Due to its energy cleanliness and high efficiency, the construction of LNG receiving stations has been rapidly promoted in China, becoming an important node connecting the domestic and international LNG supply chains. The construction and development of LNG receiving stations not only have important significance for ensuring energy security but also promote the utilization of clean energy, contributing to the optimization of the global energy structure and the realization of environmental protection goals. With the continuous growth of global energy demand and the increasing awareness of environmental protection, the number and technical level of LNG receiving stations are also constantly improving to meet the growing demand for clean energy.

[0003] During the operation of LNG receiving stations, the generation of BOG (Boil Off Gas) is an inevitable phenomenon. BOG is the gas generated due to the heat evaporation of LNG during storage and transportation, and its main component is methane. The traditional treatment method is to directly discharge BOG into the atmosphere, which not only wastes precious energy resources but also causes environmental pollution and increases greenhouse gas emissions. With the continuous expansion of the scale of LNG receiving stations, the problem of BOG treatment has become increasingly prominent. Especially in the context of large-scale, increased equipment sets, and the interconnection of receiving station groups, how to efficiently and environmentally treat BOG has become a major challenge in the operation of LNG receiving stations. Summary of the Invention

[0004] The purpose of the present invention is to provide a BOG treatment device and a BOG treatment process for LNG receiving stations to alleviate the technical problem of wasting resources by directly discharging BOG in LNG receiving stations into the atmosphere in the prior art.

[0005] In a first aspect, the BOG treatment device for LNG receiving stations provided by the present invention includes: a compression device, a cooler, and a submerged recondenser;

[0006] The compression device includes a first compressor and a second compressor arranged in parallel. The inlet ends of the first compressor and the second compressor are both connected to the LNG storage tank, so that BOG in the LNG storage tank can enter the first compressor and the second compressor;

[0007] The outlet ends of the first compressor and the second compressor are both connected to the cooler;

[0008] The submersible recondenser is in communication with the cooler so that the BOG cooled by the cooler enters the submersible recondenser. The submersible recondenser is in communication with the LNG storage tank so that the LNG in the LNG storage tank enters the submersible recondenser. The submersible recondenser is configured to enable the contact and absorption liquefaction of BOG and LNG;

[0009] The LNG in the submersible recondenser can flow back into the cooler, and the cooler is configured to enable the heat exchange between the BOG and LNG inside it.

[0010] In an alternative embodiment,

[0011] A vertically arranged baffle is provided inside the submersible recondenser, and there is a spacing between the top of the baffle and the inner wall of the submersible recondenser. The baffle is used to divide the internal space of the submersible recondenser into a gas-liquid space and a liquid phase space. The liquid in the gas-liquid space enters the liquid phase space through the spacing, and a packing layer is provided in the gas-liquid space to improve the gas-liquid mixing effect;

[0012] When the temperature difference between the gas-liquid space and the liquid phase space in the submersible recondenser is less than 4°C, the LNG supply on the liquid phase space side is started;

[0013] A gas phase distributor and a liquid phase distributor are provided on the gas-liquid space side inside the submersible recondenser. The gas phase distributor is in communication with the outlet pipeline of the cooler and is immersed at the bottom of the liquid phase LNG space in the gas-liquid space. The liquid phase distributor is connected to the LNG main pipeline;

[0014] The opening direction of the gas phase distributor is obliquely upward at an angle of 60-90° with the horizontal line, and the opening area is 1-2 times the cross-sectional area of the pipeline.

[0015] The operating pressure of the submersible recondenser is maintained at 0.6-1.2 MPa through the top regulating valve.

[0016] Among them, the LNG main pipeline on the liquid phase space side is below the LNG liquid level.

[0017] In an alternative embodiment,

[0018] The BOG treatment equipment for the LNG receiving station further includes a first desuperheater;

[0019] The inlet end of the first desuperheater is in communication with the LNG storage tank so that the BOG in the LNG storage tank can enter the first desuperheater;

[0020] The outlet end of the first desuperheater is respectively communicated with the first compressor and the second compressor;

[0021] A spray pipe is arranged in the first desuperheater. The spray pipe is communicated with the LNG storage tank. The spray pipe is used to spray the LNG in the LNG storage tank in the first desuperheater, so that the LNG is mixed with the BOG droplets to reduce the BOG temperature.

[0022] Regulate the number of stages of the spray started by the spray pipe according to the inlet temperature of the first compressor or the second compressor, and start 2-stage or 3-stage LNG spraying at -75°C to -70°C.

[0023] In an alternative embodiment,

[0024] The BOG treatment device for the LNG receiving station further includes a first high-pressure pump and a second high-pressure pump;

[0025] Both the first high-pressure pump and the second high-pressure pump are communicated with the outlet end of the submerged recondenser, both the first high-pressure pump and the second high-pressure pump are communicated with the inlet end of the cooler, and the first high-pressure pump and the second high-pressure pump are arranged in parallel;

[0026] Both the first high-pressure pump and the second high-pressure pump are used to pressurize the LNG delivered from the outlet end of the submerged recondenser and deliver the pressurized LNG to the cooler.

[0027] In an alternative embodiment,

[0028] The BOG treatment device for the LNG receiving station further includes a first regulating ball valve and a second regulating ball valve;

[0029] The first regulating ball valve is arranged on the outlet pipeline of the first high-pressure pump, and the first regulating ball valve is used to control the pressure in the outlet pipeline of the first high-pressure pump;

[0030] The second regulating ball valve is arranged on the outlet pipeline of the second high-pressure pump, and the second regulating ball valve is used to control the pressure in the outlet pipeline of the second high-pressure pump.

[0031] The first regulating ball valve and the second regulating ball valve achieve the stability of the pressure at the position of the high-pressure pump outlet header through regulation.

[0032] In an alternative embodiment,

[0033] The BOG treatment device for the LNG receiving station further includes a second desuperheater;

[0034] The second desuperheater is respectively communicated with the outlet end of the LNG storage tank and the outlet end of the cooler, and the second desuperheater is configured to enable the LNG in the LNG storage tank to be transported into the outlet pipeline of the cooler, so as to reduce the temperature of the BOG in the outlet pipeline of the cooler.

[0035] In an alternative embodiment,

[0036] The first compressor is set as a reciprocating compressor, and the second compressor is set as a centrifugal compressor. The single BOG processing capacity of the centrifugal compressor is 1.5 - 2 times that of the reciprocating compressor;

[0037] A pressure stabilizing regulating valve is arranged on the outlet pipeline of the centrifugal compressor. The pressure stabilizing regulating valve is configured to adjust the outlet pressure of the centrifugal compressor according to the outlet pressure of the reciprocating compressor, so as to balance the outlet pressures of the reciprocating compressor and the centrifugal compressor. The maximum pressure regulating range of the pressure stabilizing regulating valve does not exceed 2% of the maximum outlet pressure of the compressor.

[0038] In an alternative embodiment,

[0039] The BOG processing device for the LNG receiving terminal further includes a secondary liquefier and a liquid nitrogen storage tank;

[0040] The secondary liquefier is arranged above the submerged recooler. The secondary liquefier is communicated with the submerged recooler. The BOG in the submerged recooler can enter the secondary liquefier for condensation, and after condensation, it flows back to the submerged recooler;

[0041] The liquid nitrogen storage tank is communicated with the secondary liquefier. The liquid nitrogen storage tank is configured to be able to transport liquid nitrogen to the secondary liquefier, so that the BOG in the secondary liquefier exchanges heat with the liquid nitrogen.

[0042] In an alternative embodiment,

[0043] The BOG processing device for the LNG receiving terminal further includes a third compressor;

[0044] The outlet ends of the first compressor and the second compressor are both communicated with the third compressor. The third compressor is used to pressurize the BOG output from the outlet ends of the first compressor and the second compressor and transport it to the outside.

[0045] In a second aspect, the BOG processing process provided by the present invention based on the BOG processing device for the LNG receiving terminal includes the following steps:

[0046] BOG from the LNG storage tank enters the cooler after being compressed by the first compressor and / or the second compressor;

[0047] The BOG in the cooler exchanges heat with the LNG delivered from the submerged recondenser. The BOG after heat exchange in the cooler enters the submerged recondenser to be cooled down;

[0048] The BOG in the submerged recondenser is mixed with the low-pressure LNG from the LNG storage tank through the gas distributor.

[0049] The BOG treatment device for the LNG receiving terminal provided by the present invention has the first compressor and the second compressor arranged in parallel. The BOG transported out of the LNG receiving terminal can enter the first compressor or the second compressor. It can be selected to enter the first compressor or the second compressor according to the load condition. The BOG after being compressed by the compressor enters the cooler. The BOG after being cooled by the cooler enters the submerged recondenser to realize on-site condensation recovery. And the LNG in the submerged recondenser is pressurized and enters the cooler. The BOG from the compressor outlet in the cooler exchanges heat with the high-pressure LNG from the submerged recondenser, making full use of the cold source in the station to realize the deep recovery of BOG, achieving the technical effect of energy-saving and consumption-reducing BOG recovery, and alleviating the technical problem that the BOG in the LNG receiving terminal in the prior art is directly discharged into the atmosphere, wasting resources. Description of the Drawings

[0050] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0051] Figure 1 It is the overall structural schematic diagram of the BOG treatment device for the LNG receiving terminal provided by the embodiment of the present invention;

[0052] Figure 2 It is the structural schematic diagram of the spray pipe in the BOG treatment device for the LNG receiving terminal provided by the embodiment of the present invention.

[0053] Icon: 1 - LNG storage tank; 2 - first compressor; 3 - second compressor; 4 - cooler; 5 - submerged re - condenser; 51 - baffle; 52 - gas distributor; 53 - liquid distributor; 6 - first desuperheater; 61 - spray pipe; 7 - first high - pressure pump; 8 - second high - pressure pump; 9 - first regulating ball valve; 10 - second regulating ball valve; 11 - second desuperheater; 12 - pressure - stabilizing regulating valve; 13 - secondary liquefier; 14 - liquid nitrogen storage tank; 15 - third compressor; 100 - BOG main pipe; 200 - LNG main pipe. Detailed implementation manners

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0055] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying 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 thus cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0056] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; 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 internal communication of two elements. 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.

[0057] The following will detail the specific implementation manners of the present invention with reference to the accompanying drawings. It should be understood that the specific implementation manners described here are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0058] As Figure 1As shown in the figure, the BOG treatment equipment provided in this embodiment for an LNG receiving terminal includes a compression device, a cooler 4, and a submerged recondenser 5. The compression device includes a first compressor 2 and a second compressor 3 arranged in parallel. The first compressor 2 is set as a reciprocating compressor, and the second compressor 3 is set as a centrifugal compressor. The BOG main pipes 100 of multiple LNG storage tanks from the LNG storage tank 1 are respectively connected to the centrifugal compressor and the reciprocating compressor, so that the BOG in the LNG storage tank 1 can enter the centrifugal compressor and the reciprocating compressor.

[0059] Among them, the reciprocating compressor operates with five or three load levels, such as 0%, 25%, 50%, 75%, and 100% or 0%, 50%, 100%. The centrifugal compressor operates with variable frequency and can achieve a load handling capacity of 30% - 100%. The single BOG handling capacity of the centrifugal compressor is 1.5 - 2 times that of the reciprocating compressor.

[0060] The outlet ends of the first compressor 2 and the second compressor 3 are divided into two routes. One pipeline is connected to the cooler 4 and then enters the submerged recondenser 5 to enable the BOG cooled by the cooler 4 to enter the submerged recondenser 5. The other pipeline directly enters the third compressor 15, and the third compressor 15 is specifically set as a high-pressure BOG compressor. The two pipelines implement two BOG treatment methods: in-station condensation recovery treatment and direct external transportation treatment.

[0061] For multiple interconnected LNG receiving terminals, the multiple LNG storage tanks 1 in each LNG receiving terminal are aggregated through pipelines and connected to the BOG main pipe 100 to achieve unified treatment.

[0062] The submerged recondenser 5 is connected to the LNG storage tank 1 so that the LNG in the LNG storage tank 1 can enter the submerged recondenser 5. The submerged recondenser 5 is configured to enable the BOG to contact and absorb liquefaction with the LNG. The LNG in the submerged recondenser 5 can flow back into the cooler 4, and the cooler 4 is configured to enable the BOG inside it to exchange heat with the LNG.

[0063] The BOG treatment equipment for an LNG receiving terminal provided in this embodiment has a first compressor 2 and a second compressor 3 arranged in parallel. The BOG transported out of the LNG storage tank 1 can enter either the first compressor 2 or the second compressor 3, and can be selected to enter the first compressor 2 or the second compressor 3 according to the load condition. The BOG compressed by the compressor enters the cooler 4, and the BOG cooled by the cooler 4 enters the submerged recondenser 5 to achieve in-station condensation recovery. Moreover, the LNG in the submerged recondenser 5 is pressurized and enters the cooler 4. The BOG from the compressor outlet in the cooler 4 exchanges heat with the high-pressure LNG from the submerged recondenser 5, making full use of the in-station cold source to achieve deep recovery of BOG, realizing the technical effect of energy-saving and consumption-reducing BOG recovery, and alleviating the technical problem of wasting resources by directly discharging the BOG in the LNG storage tank 1 into the atmosphere in the prior art.

[0064] Regarding the structure of the submerged recondenser 5, specifically:

[0065] A vertically arranged baffle 51 is provided inside the submerged recondenser 5. The height of the baffle 51 is 60% - 80% of the equipment height of the submerged recondenser 5, so that there is a spacing between the baffle 51 and the top of the inner wall of the submerged recondenser 5. The baffle 51 divides the internal space of the submerged recondenser 5 into a gas-liquid space and a liquid phase space, and the liquid in the gas-liquid space enters the liquid phase space through the spacing.

[0066] A gas-phase distributor 52 and a liquid-phase distributor 53 are provided inside the submerged recondenser 5. The gas-phase distributor 52 is connected to the outlet pipeline of the cooler 4 and is immersed at the bottom of the liquid-phase LNG space in the gas-liquid space. The liquid-phase distributor 53 is connected to the LNG main pipeline 200. The low-temperature BOG enters the bottom of the gas-liquid two-phase zone, and the bubbles obtained through the small holes on the disc tube of the gas-phase distributor 52 enter the liquid phase space. At the same time, the packing layer is used to increase the contact area.

[0067] The opening direction of the gas-phase distributor 52 is obliquely upward at an angle of 60 - 90° with the horizontal line, and the opening area is 1 - 2 times the cross-sectional area of the pipeline. The operating pressure of the submerged recondenser 5 is maintained at 0.6 - 1.2 Mpa through the top regulating valve. Among them, the LNG main pipeline 200 on the liquid phase space side is below the LNG liquid level.

[0068] When the temperature difference TXY between the temperature T21 in the gas-liquid space and the temperature T22 in the liquid phase space, that is, T21 - T22, is lower than 4°C, start the LNG supply on the liquid phase space side.

[0069] In an alternative embodiment, the BOG treatment device for the LNG receiving terminal further includes a first desuperheater 6; the inlet end of the first desuperheater 6 is connected to the LNG storage tank 1 so that the BOG in the LNG storage tank 1 can enter the first desuperheater 6; the outlet end of the first desuperheater 6 is respectively connected to the first compressor 2 and the second compressor 3; a spray pipe 61 is arranged in the first desuperheater 6, and the spray pipe 61 is connected to the LNG storage tank 1. The spray pipe 61 is used to spray the LNG in the LNG storage tank 1 in the first desuperheater 6 so that the LNG is mixed with the BOG droplets to reduce the temperature of the BOG.

[0070] Specifically, the first desuperheater 6 is specifically arranged as a spray desuperheater tank. A branch is led out from the low-pressure LNG main pipe 200 and enters the spray desuperheater tank. It enters the tank through multiple spray pipe 61 lines, and 2-3 stages of spray coil pipes are arranged inside; the BOG enters the spray desuperheater tank from the BOG main pipe 100 and is mixed with the sprayed low-pressure LNG droplets. The inlet temperature of the spray desuperheater tank is above -50°C, and 2-3 stages of LNG spray cooling are started. When the inlet temperature is relatively low, a single-stage coil pipe spray can be enabled. The opening direction of the spray holes of the spray coil pipe is obliquely upward, and the angle with the horizontal line is 60-90°.

[0071] As Figure 2 shown, the number of stages of the spray started by the spray pipe 61 is regulated according to the inlet temperature of the first compressor 2 or the second compressor 3, and 2-stage or 3-stage LNG spray is started at 75-70°C.

[0072] In an alternative embodiment, the BOG treatment device for the LNG receiving terminal further includes a first high-pressure pump 7 and a second high-pressure pump 8; both the first high-pressure pump 7 and the second high-pressure pump 8 are connected to the outlet end of the submersible recondenser 5, both the first high-pressure pump 7 and the second high-pressure pump 8 are connected to the inlet end of the cooler 4, and the first high-pressure pump 7 and the second high-pressure pump 8 are arranged in parallel; both the first high-pressure pump 7 and the second high-pressure pump 8 are used to pressurize the LNG delivered from the outlet end of the submersible recondenser 5 and deliver the pressurized LNG to the cooler 4.

[0073] Specifically, the low-pressure BOG enters the cooler 4 after being compressed by the compressor. The high-pressure LNG in the outlet pipelines of the first high-pressure pump 7 and the second high-pressure pump 8 is used to exchange heat with the BOG at the outlet of the BOG compressor in the cooler 4 to reduce the temperature of the BOG entering the submersible recondenser 5.

[0074] In an optional embodiment, the BOG processing equipment for the LNG receiving station also includes a first regulating ball valve 9 and a second regulating ball valve 10; the first regulating ball valve 9 is arranged on the outlet pipeline of the first high-pressure pump 7, and the first regulating ball valve 9 is used to control the pressure in the outlet pipeline of the first high-pressure pump 7; the second regulating ball valve 10 is arranged on the outlet pipeline of the second high-pressure pump 8, and the second regulating ball valve 10 is used to control the pressure in the outlet pipeline of the second high-pressure pump 8. The first regulating ball valve 9 and the second regulating ball valve 10 are both configured as adjustable shut-off ball valves, which can not only realize the shut-off function, but also adjust the outlet pressure of a single pump, thereby solving the problem of inconsistent pressure at the confluence point due to the different distances of the pipelines due to the layout of the high-pressure pumps, resulting in vibration and pump failure.

[0075] The first regulating ball valve 9 and the second regulating ball valve 10 can achieve pressure stability at the outlet manifold of the high-pressure pump by adjusting, and are suitable for 4 to 12 pumps in parallel.

[0076] In an optional embodiment, the BOG processing equipment for the LNG receiving station also includes a second desuperheater 11; the second desuperheater 11 is connected to the outlet end of the LNG storage tank 1 and the outlet end of the cooler 4 respectively, and the second desuperheater 11 is configured to enable the LNG in the LNG storage tank 1 to be transported to the outlet pipeline of the cooler 4 to reduce the temperature of the BOG in the outlet pipeline of the cooler 4. When the outlet temperature of the low-pressure BOG compressor is high, the second desuperheater 11 is used to reduce the temperature. The LNG of the second desuperheater 11 comes from the low-pressure LNG main pipe 200 and is further cooled to below -135°C by the secondary desuperheater. Two-stage cooling is achieved by the cooler 4 and the secondary desuperheater to reduce the load of the submerged recondenser 5 as much as possible. The operating pressure of the submerged recondenser 5 is between 0.6 and 1.5 MPa, and the pressure is controlled by a regulating valve.

[0077] In an optional embodiment, a pressure-stabilizing regulating valve 12 is provided on the outlet pipeline of the centrifugal compressor. The pressure-stabilizing regulating valve 12 is configured to adjust the outlet pressure of the centrifugal compressor according to the outlet pressure of the reciprocating compressor to balance the outlet pressures of the reciprocating compressor and the centrifugal compressor, and adjust the outlet pressures of compressors of different models according to the outlet pressure of the reciprocating BOG compressor to achieve pressure balance. The pressure is adjusted in the range of 0 to 2%, thereby minimizing the pressure energy loss caused by pressure reduction.

[0078] The single - unit operating load of the centrifugal compressor can be steplessly adjusted from 30% to 100%. The single - unit operating load of the reciprocating compressor can be adjusted in five levels of 0%, 25%, 50%, 75%, and 100%, or in three levels of 0%, 50%, and 100%. When the BOG throughput is greater than the rated throughput of the centrifugal compressor, the centrifugal compressor V is preferentially started. Considering the advantage of the centrifugal compressor in handling large flow rates, when the BOG throughput is greater than the rated throughput of the centrifugal compressor, the centrifugal compressor is preferentially started. However, in the case of low loads, the reciprocating compressor can be used.

[0079] In an alternative embodiment, the BOG treatment device for the LNG receiving terminal further includes a secondary liquefier 13 and a liquid nitrogen storage tank 14. The secondary liquefier 13 is arranged above the submerged re - condenser 5. The secondary liquefier 13 is in communication with the submerged re - condenser 5. The BOG in the submerged re - condenser 5 can enter the secondary liquefier 13 for condensation, and after condensation, it flows back to the submerged re - condenser 5. The liquid nitrogen storage tank 14 is in communication with the secondary liquefier 13, and the liquid nitrogen storage tank 14 is configured to be able to transport liquid nitrogen to the secondary liquefier 13 so that the BOG in the secondary liquefier 13 exchanges heat with the liquid nitrogen.

[0080] The excessive gas phase generated at the top of the submerged re - condenser 5 enters the secondary liquefier 13 through a pipeline and is further condensed by the liquid nitrogen, and then flows back to the liquid phase area of the submerged re - condenser 5 through a pipeline.

[0081] The liquid nitrogen comes from the on - site liquid nitrogen storage tank 14, enters the liquid nitrogen vaporizer after being heated in the secondary liquefier 13. The excess liquid nitrogen directly enters the liquid nitrogen vaporizer, and then the reheated nitrogen enters the nitrogen users of the receiving terminal.

[0082] It should be noted that the layout height of the BOG secondary liquefier 13 is higher than that of the submerged re - condenser 5. The sub - cooled LNG condensed by the liquid nitrogen enters the liquid phase space of the submerged re - condenser 5 by gravity. The inside of the BOG secondary liquefier 13 uses a shell - and - tube heat exchanger. The liquid level of the liquid nitrogen is above 85%, and the flow rate of the liquid nitrogen entering is controlled by the liquid level.

[0083] The BOG treatment device for the LNG receiving terminal provided in this embodiment has the following advantages:

[0084] (1) Utilize the characteristics of the large - flow centrifugal BOG compressor to handle the BOG generated by the large - scale LNG storage tank 1. At the same time, considering the actual start - up conditions of the BOG compressor, desuperheaters are set at different positions to meet the start - up requirements.

[0085] (2) In order to reduce the difference in the outlet pressure of each pump after multiple high - pressure pumps are connected in parallel, an adjustable shut - off ball valve is set at the outlet of the high - pressure pump.

[0086] (3) The present invention provides an immersion condenser and a secondary liquefier 13 to fully utilize the cold source in the station to achieve deep recovery of BOG.

[0087] (4) This process and device are applicable to the BOG treatment of large LNG storage tanks 1 or the BOG treatment of multiple interconnected LNG storage tanks 1, and can achieve the purpose of energy conservation, consumption reduction, and stable operation.

[0088] Based on the above embodiments, the BOG treatment process provided in this embodiment for the BOG treatment equipment for an LNG receiving station includes the following steps: The BOG from the LNG storage tank 1 is compressed by the first compressor 2 and / or the second compressor 3 and then enters the cooler 4; the BOG in the cooler 4 exchanges heat with the LNG delivered from the immersion recondenser 5, and the BOG after heat exchange in the cooler 4 enters the immersion recondenser 5 to be cooled down; the BOG in the immersion recondenser 5 is mixed with the LNG droplets from the LNG storage tank 1.

[0089] Since the technical effects of the BOG treatment process provided in this embodiment for the BOG treatment equipment for an LNG receiving station are the same as those of the BOG treatment equipment for an LNG receiving station provided in the above embodiments, they will not be elaborated here.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A BOG treatment device for an LNG receiving terminal, characterized in that, Comprising: A compression device, a cooler (4) and a submerged re-condenser (5); The compression device includes a first compressor (2) and a second compressor (3) arranged in parallel. The inlet ends of the first compressor (2) and the second compressor (3) are both connected to the LNG storage tank (1) so that the BOG in the LNG storage tank (1) can enter the first compressor (2) and the second compressor (3); The outlet ends of the first compressor (2) and the second compressor (3) are both connected to the cooler (4); The submerged re-condenser (5) is connected to the cooler (4) so that the BOG cooled by the cooler (4) enters the submerged re-condenser (5). The submerged re-condenser (5) is connected to the LNG storage tank (1) so that the LNG in the LNG storage tank (1) enters the submerged re-condenser (5). The submerged re-condenser (5) is configured to enable the BOG to contact and absorb liquefaction with the LNG; The LNG in the submerged re-condenser (5) can flow back into the cooler (4), and the cooler (4) is configured to enable the BOG inside it to exchange heat with the LNG.

2. The BOG treatment device for an LNG receiving terminal according to claim 1, characterized in that A vertically arranged baffle (51) is provided inside the submerged re-condenser (5), and there is a spacing between the baffle (51) and the top of the inner wall of the submerged re-condenser (5). The baffle (51) is used to divide the internal space of the submerged re-condenser (5) into a gas-liquid space and a liquid phase space. The liquid in the gas-liquid space enters the liquid phase space through the spacing, and a packing layer is provided in the gas-liquid space to improve the gas-liquid mixing effect; When the temperature difference between the gas-liquid space and the liquid phase space is less than 4°C, start the LNG supply on the liquid phase space side; A gas phase distributor (52) and a liquid phase distributor (53) are provided on the gas-liquid space side inside the submerged re-condenser (5). The gas phase distributor (52) is connected to the outlet pipeline of the cooler (4), and the gas phase distributor (52) is immersed at the bottom of the liquid phase LNG space in the gas-liquid space. The liquid phase distributor (53) is connected to the LNG main pipe (200); The opening direction of the gas phase distributor (52) is obliquely upward at an angle of 60-90° with the horizontal line, and the opening area is 1-2 times the cross-sectional area of the pipeline; The operating pressure of the submerged re-condenser (5) is maintained at 0.6-1.2 Mpa through the top regulating valve; Wherein, the LNG main pipe (200) on the liquid phase space side is below the LNG liquid level.

3. The BOG treatment device for an LNG receiving terminal according to claim 1, characterized in that The BOG treatment device for an LNG receiving terminal further includes a first temperature reducer (6); The inlet end of the first temperature reducer (6) is connected to the LNG storage tank (1) so that the BOG in the LNG storage tank (1) can enter the first temperature reducer (6); The outlet end of the first desuperheater (6) is respectively communicated with the first compressor (2) and the second compressor (3); A spray pipe (61) is arranged in the first desuperheater (6). The spray pipe (61) is communicated with the LNG storage tank (1). The spray pipe (61) is used for spraying the LNG in the LNG storage tank (1) in the first desuperheater (6) so that the LNG is mixed with the BOG droplets to reduce the BOG temperature; The number of stages of the spray started by the spray pipe (61) is regulated according to the inlet temperature of the first compressor (2) or the second compressor (3). Two-stage or three-stage LNG spraying is started at -75 to -70 °C.

4. The BOG treatment device for an LNG receiving terminal according to claim 1, wherein The BOG treatment device for an LNG receiving terminal further comprises a first high-pressure pump (7) and a second high-pressure pump (8); Both the first high-pressure pump (7) and the second high-pressure pump (8) are communicated with the outlet end of the submerged recondenser (5). Both the first high-pressure pump (7) and the second high-pressure pump (8) are communicated with the inlet end of the cooler (4). And the first high-pressure pump (7) and the second high-pressure pump (8) are arranged in parallel; Both the first high-pressure pump (7) and the second high-pressure pump (8) are used for pressurizing the LNG conveyed out from the outlet end of the submerged recondenser (5) and conveying the pressurized LNG to the cooler (4).

5. The BOG treatment device for an LNG receiving terminal according to claim 4, wherein The BOG treatment device for an LNG receiving terminal further comprises a first regulating ball valve (9) and a second regulating ball valve (10); The first regulating ball valve (9) is arranged on the outlet pipeline of the first high-pressure pump (7). The first regulating ball valve (9) is used for controlling the pressure in the outlet pipeline of the first high-pressure pump (7); The second regulating ball valve (10) is arranged on the outlet pipeline of the second high-pressure pump (8). The second regulating ball valve (10) is used for controlling the pressure in the outlet pipeline of the second high-pressure pump (8); The first regulating ball valve (9) and the second regulating ball valve (10) achieve the stability of the pressure at the position of the high-pressure pump outlet header through regulation.

6. The BOG treatment device for an LNG receiving terminal according to claim 1, wherein The BOG treatment device for an LNG receiving terminal further comprises a second desuperheater (11); The second desuperheater (11) is respectively communicated with the outlet end of the LNG storage tank (1) and the outlet end of the cooler (4). The second desuperheater (11) is configured to be able to convey the LNG in the LNG storage tank (1) into the outlet pipeline of the cooler (4) to reduce the temperature of the BOG in the outlet pipeline of the cooler (4).

7. The BOG treatment device for an LNG receiving terminal according to claim 1, wherein The first compressor (2) is set as a reciprocating compressor, and the second compressor (3) is set as a centrifugal compressor. The single-unit BOG processing capacity of the centrifugal compressor is 1.5 - 2 times that of the reciprocating compressor. A pressure stabilizing regulating valve (12) is arranged on the outlet pipeline of the centrifugal compressor. The pressure stabilizing regulating valve (12) is configured to adjust the outlet pressure of the centrifugal compressor according to the outlet pressure of the reciprocating compressor, so as to balance the outlet pressures of the reciprocating compressor and the centrifugal compressor. The maximum pressure range of adjustment of the pressure stabilizing regulating valve (12) does not exceed 2% of the maximum outlet pressure of the compressor.

8. The BOG processing device for an LNG receiving terminal according to claim 1, wherein the BOG processing device for an LNG receiving terminal further comprises a secondary liquefier (13) and a liquid nitrogen storage tank (14); The secondary liquefier (13) is arranged above the submerged recooler (5). The secondary liquefier (13) is communicated with the submerged recooler (5). The BOG in the submerged recooler (5) can enter the secondary liquefier (13) for condensation, and after condensation, it flows back to the submerged recooler (5). The liquid nitrogen storage tank (14) is communicated with the secondary liquefier (13). The liquid nitrogen storage tank (14) is configured to be able to transport liquid nitrogen to the secondary liquefier (13) so that the BOG in the secondary liquefier (13) exchanges heat with the liquid nitrogen.

9. The BOG processing device for an LNG receiving terminal according to claim 1, wherein the BOG processing device for an LNG receiving terminal further comprises a third compressor (15); The outlet ends of the first compressor (2) and the second compressor (3) are both communicated with the third compressor (15). The third compressor (15) is used to pressurize the BOG output from the outlet ends of the first compressor (2) and the second compressor (3) and transport it to the outside.

10. A BOG treatment process for a BOG treatment device for an LNG receiving terminal as described in any one of claims 1-9, characterized in that, including the following steps: The BOG from the LNG storage tank (1) enters the cooler (4) after being compressed by the first compressor (2) and / or the second compressor (3); The BOG in the cooler (4) exchanges heat with the LNG transported from the submerged recooler (5). The BOG after heat exchange in the cooler (4) enters the submerged recooler (5) to be cooled down; The BOG in the submerged recooler (5) realizes gas-liquid mixing with the low-pressure LNG from the LNG storage tank (1) through the gas distributor (52).

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