A cold conservation circulation and recondenser system for an LNG receiving terminal wharf

Abstract

The application provides a cold insulation circulation and recondenser system of an LNG receiving station wharf, which comprises an external delivery main pipe, a first interface, a second interface, a third interface, a fourth interface and a fifth interface arranged in sequence along a fluid flow direction, an LNG storage tank, an outlet of the LNG storage tank being communicated with the first interface, a cold insulation circulation cross line, one end of the cold insulation circulation cross line being communicated with the second interface, a first valve being arranged on the cold insulation circulation cross line, a cold insulation circulation pipeline, the cold insulation circulation pipeline being communicated with the other end of the cold insulation circulation cross line, an unloading main pipe, the unloading main pipe being connected with an inlet of the LNG storage tank through an LNG storage tank inlet pipeline and being capable of being connected with an unloading arm of an LNG ship, the cold insulation circulation pipeline being connected with the unloading main pipe at the wharf, the unloading main pipe being connected with the fourth interface through an unloading cross line, a recondenser, an inlet of the recondenser being connected with the third interface, and an outlet of the recondenser being connected with the fifth interface.

Description

Technical Field

[0001] This invention relates to the field of LNG equipment, and in particular to a cold storage circulation and recondenser system for an LNG receiving terminal. Background Technology

[0002] LNG receiving terminals generate a large amount of boil-off gas (BOG) during operation. The BOG recondensation process involves compressing the BOG to a certain pressure, then mixing and condensing it with LNG supplied by the low-pressure delivery pump in the tank in a recondenser. The condensed LNG is then pressurized by the high-pressure output pump and exported. Therefore, the recondensation process utilizes the cooling capacity of LNG, reducing BOG compression energy consumption and thus saving energy. This is typically suitable for large-scale LNG receiving terminals with a sustainable gas supply capacity. During periods when the terminal is not unloading, a portion of the LNG from the low-pressure output main circulates through the cold insulation and unloading pipelines to keep the LNG unloading pipelines cold.

[0003] The existing technology has the following problems in actual operation:

[0004] 1. Atmospheric temperature, wind speed, season, and diurnal variation at the LNG receiving terminal all affect the quality of the cold energy returned by the terminal's cold storage circulation and the LNG return temperature. Therefore, the temperature and flow rate of the LNG returned by the terminal's cold storage circulation fluctuate with different seasons, time periods, and weather conditions, resulting in significant fluctuations in the temperature of the LNG entering the recooler to cool the BOG. ​​The change in the temperature of the LNG, which serves as the cold source, is one of the main factors affecting the stability of the recooler's operating pressure and level control. The change in LNG temperature further affects the fluctuations in the recooler's operating level and pressure during actual operation, which in turn affects the fluctuations in the high-pressure pump inlet pressure, and in severe cases, causes alarms and interlocks in the safety instrument system.

[0005] 2. In order to realize the return of the flow stream through the cold storage circulation at the wharf to the main export pipeline, the existing design requires the installation of a control valve to achieve hydraulic matching. Therefore, the operating pressure drop of the control valve should be equal to the hydraulic pressure drop of the cold storage circulation pipeline loop, which is usually about 100-200 kPaG. The head of the low-pressure transfer pump in the LNG storage tank needs to take into account this control valve, providing an additional 100-200 kPaG of pressure head. This increases the investment in equipment and instrumentation for the project, as well as the energy consumption during the operation of the receiving station.

[0006] Therefore, the current LNG receiving terminal cold storage cycle and recondenser process has poor adaptability to changes in operating conditions and ambient temperature, high operating costs, large investment, and high energy consumption. Summary of the Invention

[0007] The main objective of this invention is to provide a cold storage circulation and recondenser system for LNG receiving terminal terminals, aiming to solve the technical problem of poor adaptability of existing technologies.

[0008] This invention proposes a cold storage circulation and recondenser system for an LNG receiving terminal, comprising:

[0009] An external transmission main pipe, wherein the external transmission main pipe has a first interface, a second interface, a third interface, a fourth interface and a fifth interface arranged sequentially along the fluid flow direction;

[0010] An LNG storage tank, the outlet of which is connected to the first interface;

[0011] A cold insulation circulation crossover line is provided, one end of which is connected to the second interface; a first valve is provided on the cold insulation circulation crossover line.

[0012] A cold insulation circulation pipeline, wherein the other end of the cold insulation circulation pipeline is connected to the other end of the cold insulation circulation cross-line;

[0013] The unloading manifold is connected to the inlet of the LNG storage tank via an LNG storage tank inlet pipeline and can be connected to the unloading arm of the LNG ship; the cold insulation circulation pipeline is connected to the unloading manifold at the dock, and the unloading manifold is connected to the fourth interface via an unloading cross line.

[0014] A recondenser, the inlet of which is connected to the third interface, and the outlet of which is connected to the fifth interface.

[0015] Optionally, the main outlet pipe is also equipped with a pressure sensor, which is located after the fifth interface in the fluid flow direction, and the pressure sensor is electrically connected to the pressure controller; a second valve and a first pressure control valve are provided on the unloading cross line; the first pressure control valve is electrically connected to the pressure controller.

[0016] Optionally, a third valve and a second pressure control valve are provided on the main export pipe; the second pressure control valve is electrically connected to the pressure controller; wherein the third valve and the second pressure control valve are located between the third interface and the fourth interface.

[0017] Optionally, a sixth interface is provided between the third valve and the second pressure control valve, and a seventh interface is provided between the second pressure control valve and the fourth interface. The sixth interface is connected to the inlet of the pressure control bypass, and the seventh interface is connected to the outlet of the pressure control bypass. The pressure control bypass is provided with a first flow transmitter and a third pressure control valve. The third pressure control valve is electrically connected to the level controller.

[0018] Optionally, the cold insulation cycle and recondenser system further includes a first flow calculator connected to the first flow transmitter; the first flow calculator is connected to a first differential pressure calculator, which is connected to the pressure controller; the external main pipe is also provided with a first temperature transmitter connected to a temperature calculator, which is connected to the first differential pressure calculator.

[0019] Optionally, the cold storage cycle and recondenser system further includes: a subcooled LNG input pipeline, through which the third interface is connected to the inlet of the recondenser; the subcooled LNG input pipeline is equipped with a second temperature transmitter, a second flow transmitter, and a flow control valve; the second flow transmitter is connected to a flow controller, and the flow controller is connected to a second flow calculator. The second flow calculator is connected to both a first differential pressure calculator and a second differential pressure calculator.

[0020] Optionally, the cold insulation cycle and recondenser system further includes: a BOG inlet line connected to the recondenser for injecting BOG into the recondenser; a pressure transmitter, a third flow transmitter, a third temperature transmitter, and a fourth temperature transmitter installed on the BOG inlet line; the pressure transmitter, the third flow transmitter, and the third temperature transmitter are all connected to a first flow compensation calculator; the third temperature transmitter is connected to a second flow calculator, and the first temperature transmitter is connected to the second flow calculator; the second flow calculator is connected to the pressure controller.

[0021] Optionally, the recondenser is equipped with a level transmitter and a level controller connected to the level transmitter, and the level controller is connected to the first flow calculator.

[0022] Optionally, the first flow calculator is connected to the BOG compressor.

[0023] Optionally, the recondenser includes a distribution plate, a packing layer, and a vortex breaker, wherein the distribution plate and the packing layer are spaced apart along the fluid flow direction; the vortex breaker is located at the bottom of the recondenser, directly opposite the outlet of the recondenser; the outlet of the recondenser is connected to the fifth interface through a mixed LNG outlet pipeline, and a fourth valve is provided on the mixed LNG outlet pipeline.

[0024] Optionally, the system further includes a fifth valve, the two ends of which are respectively connected to the cold insulation circulation pipeline and the unloading main pipe.

[0025] Compared with the prior art, the beneficial effects of this invention are: by crossing the low-pressure export pipeline through the unloading main pipeline, the LNG in the cold storage cycle is returned to the recondenser outlet, and the operation process is simple and stable; it is less affected by the export volume and ambient temperature, and does not require frequent adjustment of the recondenser operating parameters according to the export volume and ambient temperature, thus overcoming the shortcomings of poor environmental adaptability and poor adaptability to changes in operating conditions of traditional recondenser processes, and has strong stability. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the cold storage cycle and recondenser system of the LNG receiving terminal of the present invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0030] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0031] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0032] In the prior art, at the LNG receiving terminal, the refrigeration cycle returns to the recondenser outlet, mixes with the LNG from the control valve, does not enter the recondenser, and after mixing with the LNG at the recondenser outlet, enters the high-pressure LNG pump inlet manifold. Another part of the LNG enters the high-pressure LNG pump inlet manifold after being combined with the LNG from the recondenser outlet pipeline through the recondenser bypass pipeline and valve.

[0033] Therefore, the temperature and flow rate of LNG returned from the terminal's cold storage circulation fluctuate constantly with different seasons, time periods, and weather conditions. This causes significant fluctuations in the temperature of the LNG entering the recooler to cool the BOG. ​​As the cold source, the LNG temperature is one of the main factors affecting the stability of the recooler's operating pressure and level control. Consequently, fluctuations in the recooler's operating level and pressure, as well as the high-pressure pump inlet pressure, occur during actual operation. In severe cases, this can trigger alarms and interlocks in the safety instrument system.

[0034] This invention provides a cold storage circulation and recondenser system for an LNG receiving terminal, comprising an external main pipe 110 having a first interface, a second interface, a third interface, a fourth interface, and a fifth interface arranged sequentially along the fluid flow direction.

[0035] LNG storage tank 105, the outlet of LNG storage tank 105 is connected to the first interface;

[0036] A cold insulation circulation crossover 138 is provided, one end of which is connected to the second interface; a first valve 108 is provided on the cold insulation circulation crossover 138.

[0037] The cold insulation circulation pipeline 107 is connected to the other end of the cold insulation circulation cross-line 138;

[0038] The unloading manifold 102 is connected to the inlet of the LNG storage tank 105 via the inlet pipeline of the LNG storage tank 105, and can be connected to the unloading arm of the LNG ship; the cold insulation circulation pipeline 107 is connected to the unloading manifold 102 at the dock, and the unloading manifold 102 is connected to the fourth interface.

[0039] The recondenser 116 has its inlet connected to the third interface and its outlet connected to the fifth interface.

[0040] In the technical solution of this invention embodiment, during the cold insulation cycle, the first valve 108 is in the conducting state; LNG is output from the LNG storage tank 105 to the external transmission main 110 through the first interface, and a portion of the LNG enters the cold insulation cycle pipeline 107 and the unloading main 102 sequentially through the second interface cold insulation cycle crossover 138 to achieve cold insulation of the unloading main 102. The LNG entering the unloading main 102 flows back to the fourth interface through the unloading crossover 146, and then flows back to the external transmission main 110, from which it is sent to external equipment / systems; another portion of the LNG enters the recondenser 116 through the third interface of the external transmission main, mixes with BOG, and then the mixed fluid flows back to the external transmission main through the fifth interface. Since the LNG entering the unloading manifold 102 flows into the export manifold 110 through the fourth interface, this portion of LNG will not enter the re-condenser 116. Consequently, the temperature of the LNG used by the re-condenser to cool the BOG will not be affected by seasonal fluctuations, different time periods, or different weather conditions, thus improving the system's environmental adaptability. Furthermore, there is no need to control the pressure of the LNG flowing through the terminal's insulation cycle using control valves to accommodate the hydraulic pressure drop in the insulation cycle pipeline loop, reducing the project's equipment and instrumentation investment and decreasing energy consumption during terminal operation.

[0041] In addition, when unloading LNG from the LNG ship, the first valve 108 is in the closed state. At this time, the unloading manifold 102 is connected to the unloading arm of the LNG ship, and then the LNG is transported to the LNG storage tank 105 by the unloading manifold 102 and the LNG inlet pipeline 103.

[0042] Optionally, the export main 110 is also equipped with a pressure sensor 147, which is located after the fifth interface in the fluid flow direction. The pressure sensor 147 is electrically connected to the pressure controller 132. The system also includes an unloading crossover 146, through which the unloading main 102 is connected to the fourth interface. The unloading crossover 146 is equipped with a second valve 136 and a first pressure control valve 137. The first pressure control valve 137 is electrically connected to the pressure controller 132. The first pressure control valve 137 of the unloading main crossover is controlled by the pressure controller 132 to ensure that the LNG returned from the cold storage cycle can enter the low-pressure export main 110.

[0043] Optionally, a third valve 140 and a second pressure control valve 141 are provided on the main export pipeline; the second pressure control valve 141 is electrically connected to the pressure controller 132; wherein the third valve 140 and the second pressure control valve 141 are located between the third interface and the fourth interface. The second pressure control valve 141 of the subcooled LNG transmission pipeline is controlled by the pressure controller 132, and the opening of the second pressure control valve 141 is increased when the mixed liquid pressure is lower than the set value.

[0044] Optionally, a sixth interface is provided between the third valve 140 and the second pressure control valve 141, and a seventh interface is provided between the second pressure control valve 141 and the fourth interface. The sixth interface is connected to the inlet of the pressure control bypass 139, and the seventh interface is connected to the outlet of the pressure control bypass 139. The pressure control bypass 139 is provided with a first flow transmitter 142 and a third pressure control valve 143. The third pressure control valve 143 of the pressure control valve bypass 139 is connected to the pressure controller 132. When the second pressure control valve 141 is at its maximum opening and the mixed liquid pressure is still lower than the set value, the third pressure control valve 143 is increased.

[0045] Optionally, the cold storage cycle and recondenser system also includes a first flow rate calculator 135, which is connected to a first flow transmitter 142; the first flow rate calculator 135 is connected to a first differential pressure calculator 130, which is connected to a pressure controller 132; the external main pipe 110 is also equipped with a first temperature transmitter 148, which is connected to a temperature calculator 133, which is connected to the first differential pressure calculator 130. The LNG storage tank 105 is equipped with a level transmitter 134 and a level controller 129 connected to the level transmitter 134, and the level controller 129 is connected to the first flow rate calculator 135.

[0046] Optionally, the cold storage cycle and recondenser system further includes: a subcooled LNG input line 112, with a third interface connected to the inlet of the recondenser 116 via the subcooled LNG input line 112; a second temperature transmitter 113, a second flow transmitter 114, and a flow control valve 115 are provided on the subcooled LNG input line 112; the second flow transmitter 114 is connected to a flow controller 128, and the flow controller 128 is connected to a second flow calculator 124. The second flow calculator 124 is connected to a first differential pressure calculator 130 and a second differential pressure calculator 131, respectively.

[0047] Optionally, the cold insulation cycle and recondenser system further includes: a BOG inlet line 127, which is connected to the recondenser 116 for injecting BOG into the recondenser 116; a pressure transmitter 120, a third flow transmitter 121, a third temperature transmitter 125, and a fourth temperature transmitter 126 are installed on the BOG inlet line 127; the pressure transmitter 120, the third flow transmitter 121, and the third temperature transmitter 125 are all connected to the first flow compensation calculator 122; the third temperature transmitter 125 is connected to the second flow calculator 124, and the first temperature transmitter 113 is connected to the second flow calculator 124.

[0048] Optionally, the first flow calculator 135 is connected to the level controller 129.

[0049] Optionally, the first flow calculator 135 is connected to the BOG compressor.

[0050] In specific implementation, the subcooled LNG input pipeline 112 is connected to the external transmission main 110 via a third interface and is connected to the recondenser 116 to transport LNG from the low-pressure external transmission main 110 to the recondenser 116. The subcooled LNG input pipeline 112 of the recondenser is sequentially equipped with a sixth valve 111, a flow control valve 115, a second flow transmitter 114, and a second temperature transmitter 113. The second flow transmitter 114 is connected to a flow controller 128, and the second temperature transmitter 113 is connected to a second flow calculator 124.

[0051] The BOG inlet line 127 is connected to the BOG compressor outlet line and is used to receive the BOG output from the BOG compressor. The BOG inlet line 127 is equipped with a BOG inlet line pressure transmitter 120, a third flow transmitter 121, a third temperature transmitter 125, and a fourth temperature transmitter 126.

[0052] The flow transmitter 121, temperature transmitter 125, and pressure transmitter 120 of the BOG inlet pipeline 127 calculate the standard volumetric flow rate of BOG through the first flow compensator 122. A pressure sensor 147 for the output mixture is added and connected to the pressure controller 132 and the second flow calculator 124 respectively. The second flow calculator 124 calculates the LNG input set value based on the mixture pressure and the standard volumetric flow rate of BOG. ​​By comparing the input set value of the second flow calculator 124 with the actual flow rate of the subcooled LNG input pipeline 112, the flow controller 128 controls the flow control valve 115 of the subcooled LNG input pipeline, thereby adjusting the LNG input amount.

[0053] The low-pressure output manifold 110 includes temperature sensors 148 (A, B, and C, at least three), a temperature calculator 133 which calculates the saturated vapor pressure for this state, and a first differential pressure calculator 130. The first differential pressure calculator 130 calculates the difference between the saturated vapor pressure (calculated by the temperature calculator 133) and the pressure transmitter 147, and transmits this signal to the first flow calculator 135. When the differential pressure is high, no signal is output; when the differential pressure is lower than a set value, the first flow calculator 135 reduces the output flow of the BOG compressor. Simultaneously, the first differential pressure calculator 130, based on the difference between the saturated vapor pressure of the temperature calculator 133 and the temperature calculator TX2 (not shown), stops the compressor via the SIS interlock when the differential pressure is lower than the low interlock set value. This ensures the mixture is always in a subcooled state, preventing cavitation in the high-pressure delivery pump.

[0054] The first pressure control valve 137 of the unloading main pipeline is controlled by the pressure controller 132 to ensure that the LNG returning from the cold storage cycle can enter the low-pressure transmission main pipeline 110. The second pressure control valve 141 of the subcooled LNG transmission pipeline is also controlled by the pressure controller 132. When the mixed liquid pressure is lower than the set value, the opening of the second pressure control valve 141 is increased. The third pressure control valve 143 of the pressure control valve bypass 139 is connected to the pressure controller 132. When the second pressure control valve 141 is at its maximum opening and the mixed liquid pressure is still lower than the set value, the third pressure control valve 143 is increased.

[0055] The first flow transmitter 142 is connected to the first flow calculator 135. When the flow rate is less than the required amount of subcooled LNG, the first flow calculator 135 reduces the BOG compressor outlet flow rate. When the first flow calculator 135 receives the liquid level from the recondenser level controller 129, it must control and reduce the BOG output flow rate of the BOG compressor if the liquid level is lower than the minimum liquid level, the differential pressure of the first differential pressure calculator 130 is less than the minimum differential pressure, or the subcooled LNG flow rate of the first flow transmitter 142 is less than the set value.

[0056] Optionally, the recondenser 116 includes a distribution plate 117, a packing layer 118, and a vortex breaker 119. The distribution plate 117 and the packing layer 118 are spaced apart along the fluid flow direction. The vortex breaker 119 is located at the bottom of the recondenser, directly opposite the outlet of the recondenser 116. The outlet of the recondenser 116 is connected to a fifth interface via a mixed LNG outlet pipeline 144, and a fourth valve 145 is provided on the mixed LNG outlet pipeline 144. BOG, pressurized and output from the BOG compressor, enters the recondenser 116 through the top inlet of the recondenser 116. LNG from the low-pressure output main pipe 110 enters the recondenser 116 through the liquid feed pipe. BOG and LNG enter the gas-liquid distribution plate 117 together, are evenly distributed, and then enter the packing layer 118. In the packing layer 118, the BOG comes into contact with the subcooled LNG, completely condensing the BOG into LNG. After the fully condensed LNG is broken by the vortex breaker 119, it is discharged to the external transmission main 102 through the mixed LNG outlet pipeline 144 and the fourth valve 145.

[0057] Optionally, the system also includes a fifth valve 109, with its two ends connected to the cold storage circulation pipeline 107 and the unloading main pipe 102, respectively. The fifth valve 109 is installed on the unloading crossover 100, with its two ends connected to the cold storage circulation pipeline 107 and the unloading main pipe 102, respectively. During unloading, the fifth valve 109 is open, allowing LNG from the cold storage circulation pipeline 107 to flow through the unloading crossover 100, through the fifth valve 109, into the unloading main pipe 102, and then back into the LNG storage tank 105. During cold storage circulation, the fifth valve 109 is closed, preventing the cold storage circulation pipeline 107 from flowing into the unloading main pipe 102 through the fifth valve 109.

[0058] In the technical solution of this application, the interface can be a flange interface, threaded interface, or tee interface, etc., for connecting pipes.

[0059] This application addresses the shortcomings of existing technologies by providing a stable, efficient, and highly adaptable recondenser operating system. This system improves the recondenser's operational performance, reduces equipment and instrumentation investment in projects, lowers energy consumption during terminal operation, enhances the adaptability of the terminal's cold storage cycle and recondenser system to changes in operating conditions and ambient temperature, increases the system's automation rate, and provides an automation platform for the development of intelligent LNG receiving terminals.

[0060] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A cold storage circulation and recondenser system for an LNG receiving terminal, characterized in that, include: An external transmission main (110) has a first interface, a second interface, a third interface, a fourth interface and a fifth interface arranged sequentially along the fluid flow direction; LNG storage tank (105), the outlet of which is connected to the first interface; A cold-keeping circulation cross-line (138) is provided, one end of which is connected to the second interface; a first valve (108) is provided on the cold-keeping circulation cross-line (138). A cold insulation circulation pipeline (107) is connected to the other end of the cold insulation circulation cross-line (138); The unloading manifold (102) is connected to the inlet of the LNG storage tank (105) via the inlet pipeline (103) and can be connected to the unloading arm of the LNG ship; the cold storage circulation pipeline (107) is connected to the unloading manifold (102) at the dock, and the unloading manifold (102) is connected to the fourth interface via the unloading cross line (146); A recondenser (116) is provided, wherein the inlet of the recondenser (116) is connected to the third interface and the outlet of the recondenser is connected to the fifth interface; The main outlet pipe (110) is also provided with a pressure sensor (147), which is located after the fifth interface in the direction of fluid flow. The pressure sensor (147) is electrically connected to the pressure controller (132). The unloading cross line (146) is equipped with a second valve (136) and a first pressure control valve (137). The first pressure control valve (137) is electrically connected to the pressure controller (132); The main export pipeline is equipped with a third valve (140) and a second pressure control valve (141); the second pressure control valve (141) is electrically connected to the pressure controller (132); The third valve (140) and the second pressure control valve (141) are disposed between the third interface and the fourth interface; A sixth interface is provided between the third valve (140) and the second pressure control valve (141), and a seventh interface is provided between the second pressure control valve (141) and the fourth interface. The sixth interface is connected to the inlet of the pressure control bypass (139), and the seventh interface is connected to the outlet of the pressure control bypass (139). The pressure control bypass (139) is equipped with a first flow transmitter (142) and a third pressure control valve (143). The third pressure control valve (143) is connected to the pressure controller (132). The cold insulation cycle and recondenser system also includes a first flow calculator (135), which is connected to the first flow transmitter (142); the first flow calculator (135) is connected to a first differential pressure calculator (130), which is connected to the pressure controller (132); The main export pipe (110) is also equipped with a first temperature transmitter (148), which is connected to a temperature calculator (133), and the temperature calculator (133) is connected to the first differential pressure calculator (130). The cold insulation cycle and recondenser system also includes: The third interface is connected to the inlet of the recondenser (116) via the subcooled LNG input line (112); The subcooled LNG input pipeline (112) is equipped with a second temperature transmitter (113), a second flow transmitter (114) and a flow control valve (115); the second flow transmitter (114) is connected to a flow controller (128), and the flow controller (128) is connected to a second flow calculator (124); The second flow rate calculator (124) is connected to the first differential pressure calculator (130) and the second differential pressure calculator (131) respectively; The cold insulation cycle and recondenser system also includes: BOG inlet line (127), which is connected to the recondenser (116) and is used to inject BOG into the recondenser (116); A pressure transmitter (120), a third flow transmitter (121), a third temperature transmitter (125), and a fourth temperature transmitter (126) are installed on the BOG inlet pipeline (127); the pressure transmitter (120), the third flow transmitter (121), and the third temperature transmitter (125) are all connected to the first flow compensation calculator (122); The third temperature transmitter (125) is connected to the second flow calculator (124), and the first temperature transmitter is connected to the second flow calculator (124); The recondenser (116) is provided with a level transmitter (134) and a level controller (129) connected to the level transmitter (134), and the level controller (129) is connected to the first flow calculator (135). The first flow calculator (135) is connected to the BOG compressor; The recondenser (116) includes a distribution plate (117), a packing layer (118), and a vortex breaker (119). The distribution plate (117) and the packing layer (118) are spaced apart along the fluid flow direction; the vortex breaker (119) is located at the bottom of the recondenser, directly opposite the outlet of the recondenser (116); The outlet of the recondenser (116) is connected to the fifth interface via a mixed LNG outlet pipeline (144), and a fourth valve (145) is provided on the mixed LNG outlet pipeline (144).

2. The cold insulation cycle and recondenser system as described in claim 1, characterized in that, The system also includes a fifth valve (109), the two ends of which are connected to the cold insulation circulation pipeline (107) and the unloading main pipe (102), respectively.

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