A method and system for storing cryogenic liquefied hydrocarbons

Abstract

This disclosure relates to a method and system for storing cryogenic liquefied hydrocarbons. The method includes: storing liquefied hydrocarbons in an inner tank (1) of a liquefied hydrocarbon storage tank, wherein a sealing port (8) is provided at the top of the side wall of the inner tank; introducing a first portion of nitrogen gas into the top of an annular space (3) located outside the inner tank to form a nitrogen gas curtain outside the sealing port of the inner tank; and introducing a second portion of nitrogen gas into the bottom of the annular space to allow hydrocarbon-containing gas in the annular space to return to the inner tank through the sealing port. This disclosure can return hydrocarbon-containing gas in the annular space to the inner tank through the sealing port, minimizing the partial pressure of hydrocarbon-containing gas in the annular space, preventing hydrocarbon-containing gas from condensing at low temperatures, and ensuring the pressure safety of the storage tank; it can also prevent hydrocarbon-containing gas in the inner tank from entering the annular space through the sealing port under the pressure of the nitrogen gas curtain, further improving the safety of the storage tank.

Description

Technical Field

[0001] This disclosure relates to the field of chemical production, and more specifically, to a method and system for storing cryogenic liquefied hydrocarbons. Background Technology

[0002] Currently, there are two main methods for storing butane on land worldwide: pressure storage at ambient temperature and atmospheric pressure storage at cryogenic temperature. With the increasing capacity of ships and the growing maturity of large cryogenic storage tank technology, the economical and safe atmospheric pressure cryogenic storage process is being adopted more and more.

[0003] The most critical piece of equipment in cryogenic atmospheric pressure storage systems is the cryogenic atmospheric pressure storage tank. Tank structures include single-containment tanks, double-containment tanks, and full-containment tanks. Based on their installation method, they can be divided into above-ground tanks and underground tanks. Structurally, they can be categorized as single-containment tanks, double-containment tanks, and full-containment tanks. Single-containment, double-containment, and full-containment tanks are all double-layered, consisting of an inner tank and an outer tank, with insulation material filling the space between them. The internal insulation materials mainly include expanded perlite, elastic fiberglass mat, and foamed glass bricks.

[0004] Large-scale cryogenic butane storage systems often employ full-containment tanks (metal double-walled or prestressed concrete full-containment). Typically, the nitrogen purging process for cryogenic butane storage tanks involves three steps: First, the inner tank is purged, with nitrogen entering through a nitrogen purging distribution pipe at the bottom of the tank, purging the air inside to the outside. Second, the annular space between the inner and outer tanks is purged, with nitrogen entering from the inner tank into the annular space, and the air in the annular space entering through a nitrogen purging pipe at the bottom of the annular space, which then leads to the outside. Finally, the bottom insulation layer is purged, with nitrogen entering through the top corner balance port and pressure balance port into the bottom insulation layer, and the air purging through the insulation purging port to the outside.

[0005] The atmospheric boiling point of low-temperature butane varies from approximately -0.5℃ to -12℃ depending on the composition. Compared to media such as liquefied natural gas (LNG) (atmospheric storage temperature -161℃), ethylene (atmospheric storage temperature -101℃), ethane (atmospheric storage temperature -90℃), and propane (atmospheric storage temperature -42℃), butane has a relatively high atmospheric storage temperature (atmospheric storage temperature -3℃), and in cold regions, it may even be higher than the ambient temperature. Therefore, in large low-temperature butane atmospheric pressure storage tanks built in cold regions, if the ambient temperature is consistently lower than the storage temperature (such as during winter in northern my country), the butane in the annular space between the inner and outer tanks, and the gas phase space above the ceiling may condense and liquefy, leading to a decrease in tank pressure. In severe cases, this can cause negative pressure in the tank, resulting in a safety accident. Therefore, this factor should be fully considered in the design of the storage tank. Current tank designs are not suitable for cryogenic butane storage tanks in cold regions. Therefore, new processes and methods are needed to address this type of special cryogenic butane storage system. Summary of the Invention

[0006] The purpose of this disclosure is to provide a method and system for storing cryogenic liquefied hydrocarbons. The method and system provided by this disclosure are applicable to cold regions and solve the safety problems of cryogenic liquefied hydrocarbon storage tanks in cold regions.

[0007] To achieve the above objectives, the first aspect of this disclosure provides a method for storing cryogenic liquefied hydrocarbons, the method comprising the following steps: storing liquefied hydrocarbons in an inner tank of a liquefied hydrocarbon storage tank, the inner tank having a sealing port at the top of its side wall; introducing a first portion of nitrogen gas into the top of an annular space located outside the inner tank to form a nitrogen gas curtain outside the sealing port of the inner tank; and introducing a second portion of nitrogen gas into the bottom of the annular space to allow hydrocarbon-containing gas in the annular space to return to the inner tank through the sealing port.

[0008] Optionally, the sealing port is formed as an annular opening between the top of the inner tank sidewall and the ceiling; and the sealing port allows gas to flow between the inner tank and the annular space under gas pressure; a ceiling space is formed between the ceiling and the top of the liquefied hydrocarbon storage tank; the method includes: introducing the first portion of nitrogen gas into the top of the annular space via a gas curtain coil to form the nitrogen gas curtain; the gas curtain coil is disposed at the top of the annular space and surrounds the inner tank, the tube wall of the gas curtain coil forms an annular gas outlet, and the gas outlet of the gas curtain coil faces the ceiling space; optionally, the sealing port is provided with a combination material including an aluminum plate sealing ring and a sealing and cold insulation material, and the sealing and cold insulation material is disposed on the outer wall of the aluminum plate sealing ring; optionally, the sealing port material further includes fiberglass felt; optionally, the pressure at the gas outlet of the gas curtain coil is positive pressure.

[0009] Optionally, the method includes: introducing the second portion of nitrogen gas into the bottom of the annular space via an annular purge pipe, the annular purge pipe being disposed at the bottom of the annular space and surrounding the inner tank, the pipe wall of the annular purge pipe forming an annular first opening, the first opening of the annular purge pipe facing the top of the annular space; optionally, the pressure at the gas outlet of the annular purge pipe is positive pressure.

[0010] Optionally, the method includes: introducing a first portion of nitrogen into the top of the annular space and introducing a second portion of nitrogen into the bottom of the annular space when the pressure in the annular space is lower than a first preset pressure; optionally, the first preset pressure is a warning pressure value that causes negative pressure in the liquefied hydrocarbon storage tank under local winter conditions; when the pressure in the annular space reaches a second preset pressure, stopping the introduction of nitrogen into the top and bottom of the annular space; optionally, the second preset pressure is the minimum pressure value at which the liquefied hydrocarbon storage tank maintains stability.

[0011] Optionally, before storing the liquefied hydrocarbons in the inner tank of the liquefied hydrocarbon storage tank, the method further includes: using a third portion of nitrogen to sequentially purge the inner tank, the annular space, and the bottom insulation layer of the liquefied hydrocarbon storage tank with nitrogen to displace the air in the inner tank, the annular space, and the bottom insulation layer.

[0012] Optionally, the step of purging the inner tank, the annular space, and the bottom insulation layer of the liquefied hydrocarbon storage tank sequentially with a third portion of nitrogen includes:

[0013] The third part of nitrogen gas is introduced into the bottom of the inner tank through the inner tank purging pipe, and the air outlet on the top wall of the outer tank is opened so that the air in the inner tank can escape from the sealed port into the annular space and be discharged from the air outlet on the top of the tank.

[0014] Close the air outlet at the top of the tank and open the second valve on the second branch pipe that connects the annular gap purge pipe to the atmosphere, so that the third part of nitrogen gas is introduced into the bottom of the inner tank through the inner tank purge pipe and escapes from the sealed port into the annular gap space, so that the air in the annular gap space enters the annular gap purge pipe and is discharged from the second branch pipe.

[0015] Close the second valve and open the pipeline valve connecting the first and second purge pipes at the bottom of the tank. This allows the third portion of nitrogen gas to be introduced into the bottom of the inner tank via the inner tank purge pipe and escape through the sealed port into the annular space. The nitrogen gas in the annular space then enters the second purge pipe at the bottom of the tank and returns to the first purge pipe at the bottom of the tank via the connecting pipeline. It then enters the bottom insulation layer at the bottom of the tank via the first purge pipe. Finally, the air in the bottom insulation layer at the bottom of the tank is discharged through the bottom air exhaust pipe.

[0016] A second aspect of this disclosure provides a system for storing cryogenic liquefied hydrocarbons. The system includes: a liquefied hydrocarbon storage tank, a gas curtain coil, and an annular purge pipe. The liquefied hydrocarbon storage tank comprises an inner tank, an outer tank, an annular space, a ceiling, and a sealing port, with the annular space filled with insulating material. The annular space is formed by a gap between the sidewalls of the inner and outer tanks. A ceiling space is formed between the ceiling and the top of the liquefied hydrocarbon storage tank. The ceiling is positioned above the inner tank and has a gap. The top of the sidewall of the inner tank has an annular opening, which is sealed to the ceiling to form the sealing port, allowing gas in the inner tank and the annular space to pass only through the sealing port. The annular purge pipe is formed as a ring pipe located at the bottom of the annular space and surrounding the inner tank; the wall of the annular purge pipe has a first annular opening, which faces the top of the annular space; the annular purge pipe also has a second opening extending to the outside of the liquefied hydrocarbon storage tank for communication with a nitrogen source or the atmosphere; the gas curtain coil is formed as a ring pipe located at the top of the annular space and surrounding the inner tank, with a ring-shaped gas outlet on its wall, which faces the ceiling space; the gas curtain coil also has a gas inlet extending to the outside of the liquefied hydrocarbon storage tank for communication with a nitrogen source.

[0017] Optionally, the second opening of the annular purging pipe is connected to a first branch pipe and a second branch pipe, the first branch pipe being connected to a nitrogen gas source and the second branch pipe being connected to the atmosphere; and a first valve is provided on the first branch pipe and a second valve is provided on the second branch pipe.

[0018] Optionally, the system has a start-up purging state and an anti-condensation state; in the start-up purging state, the first valve on the first branch pipe is closed and the second valve on the second branch pipe is opened to connect the annular purging pipe to the atmosphere, so as to discharge the air in the annular space; in the anti-condensation state, the first valve on the first branch pipe is opened and the second valve on the second branch pipe is closed to connect the annular purging pipe to a nitrogen source, so as to introduce nitrogen into the annular space.

[0019] Optionally, the system further includes an inner tank purging pipe, a first tank bottom purging pipe, a second tank bottom purging pipe, and a tank bottom air exhaust pipe; the top wall of the outer tank has a top air outlet for communication with the atmosphere; the liquefied hydrocarbon storage tank also includes a tank bottom insulation layer disposed between the bottom walls of the inner tank and the outer tank; wherein, the gas inlet of the inner tank purging pipe is disposed outside the liquefied hydrocarbon storage tank for communication with a nitrogen source; the gas outlet of the inner tank purging pipe passes sequentially through the top wall of the outer tank and the ceiling and extends to the bottom of the inner tank; the first end of the second tank bottom purging pipe is disposed at the top of the annular space, and the second end of the second tank bottom purging pipe passes through the top wall of the outer tank and extends to the outside of the liquefied hydrocarbon storage tank; the first end of the first tank bottom purging pipe is disposed outside the liquefied hydrocarbon storage tank and connects with the second end of the second purging pipe. The two ends of the first purge pipe at the bottom of the tank are axially connected, passing through the outer tank and the annular space and extending into the bottom insulation layer, so that the gas entering the second purge pipe at the bottom of the tank from the annular space enters the bottom insulation layer through the first purge pipe at the bottom of the tank; the first end of the air exhaust pipe at the bottom of the tank is disposed in the bottom insulation layer to form a gas inlet, and there is a gap between the first end of the air exhaust pipe at the bottom of the tank and the second end of the first purge pipe at the bottom of the tank, and the second end of the air exhaust pipe at the bottom of the tank passes through the annular space and the top wall of the outer tank in sequence to form a gas outlet communicating with the atmosphere; optionally, the sealing port is provided with a sealing material, which is a combination material including an aluminum plate sealing ring and a sealing insulation material, and the sealing insulation material is disposed on the outer wall of the sealing ring; optionally, the sealing material also includes glass fiber felt.

[0020] Through the above technical solution, this disclosure introduces nitrogen gas into the bottom of the annular space of the inner tank of the liquefied hydrocarbon storage tank. This allows hydrocarbon-containing gases (such as butane) in the annular space to return to the inner tank through the sealing port, minimizing the partial pressure of hydrocarbon-containing gases in the annular space, preventing hydrocarbon-containing gases from condensing at low temperatures, and ensuring the pressure safety of the storage tank. Furthermore, nitrogen gas is introduced outside the sealing port at the top of the inner tank to form a nitrogen gas curtain. Under the pressure of the nitrogen gas curtain, hydrocarbon-containing gases in the inner tank are prevented from entering the annular space through the sealing port, further improving the safety of the storage tank.

[0021] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0023] Figure 1This is a schematic diagram of the structure of a system for storing cryogenic liquefied hydrocarbons according to one embodiment of the present disclosure;

[0024] Figure 2 This is a schematic diagram of the structure of a liquefied hydrocarbon storage tank used in one embodiment of this disclosure;

[0025] Figure 3 This is a schematic diagram of the structure of a liquefied hydrocarbon storage tank used in one embodiment of this disclosure.

[0026] Explanation of reference numerals in the attached figures

[0027] 1-Inner tank, 2-Outer tank, 3-Annular space, 4-Ceiling, 5-Air curtain coil, 6-Annular purge pipe, 7-Inner tank purge pipe, 8-Sealing port, 9-Air outlet at the top of the tank, 10-First purge pipe at the bottom of the tank, 11-Second purge pipe at the bottom of the tank, 12-Cold insulation layer at the bottom of the tank, 13-Air exhaust pipe at the bottom of the tank, 26-First valve, 27-Second valve

[0028] 14-Inner tank, 15-Outer tank, 16-Tank bottom insulation layer, 17-Foundation, 18-Foundation heating system, 19-Sealing port, 20-Ceiling, 21-Steel tank top, 22-Annular space, 23-Heat corner protection system, 24-Steam vessel, 25-Concrete tank top Detailed Implementation

[0029] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0030] In this disclosure, unless otherwise stated, the terms "first," "second," and "third" are used only to distinguish different components and do not imply any actual connection order. In this disclosure, directional terms such as "upper," "lower," "top," and "bottom" generally refer to the upper and lower, top and bottom, of the device in its normal operating state. "Inner" and "outer" refer to the outline of the device. For example, "to form a nitrogen curtain outside the sealing opening of the inner tank" means to form a nitrogen curtain within the annular space outside the sealing opening of the inner tank.

[0031] like Figure 1 As shown, the first aspect of this disclosure provides a method for storing cryogenic liquefied hydrocarbons, the method comprising the following steps:

[0032] The liquefied hydrocarbons are stored in the inner tank 1 of the liquefied hydrocarbon storage tank, and the top of the side wall of the inner tank 1 is provided with a sealing port 8.

[0033] A first portion of nitrogen gas is introduced into the top of the annular space 3 located outside the inner tank 1 to form a nitrogen gas curtain outside the sealing port 8 of the inner tank; a second portion of nitrogen gas is introduced into the bottom of the annular space 3 so that the hydrocarbon-containing gas in the annular space 3 returns to the inner tank 1 through the sealing port 8.

[0034] The method for storing cryogenic liquefied hydrocarbons disclosed herein introduces nitrogen gas into the bottom of the annular space of the inner tank of the liquefied hydrocarbon storage tank. This allows hydrocarbon-containing gases (such as butane) in the annular space to return to the inner tank through the sealing port, minimizing the partial pressure of hydrocarbon-containing gases in the annular space, preventing hydrocarbon-containing gases from condensing at low temperatures, and ensuring the pressure safety of the storage tank. Furthermore, nitrogen gas is introduced outside the sealing port at the top of the inner tank to form a nitrogen gas curtain. Under the pressure of the nitrogen gas curtain, hydrocarbon-containing gases in the inner tank are prevented from entering the annular space through the sealing port, further improving the safety of the storage tank.

[0035] The liquefied hydrocarbon storage tank used in this disclosure is a conventional full-containment tank structure in the art.

[0036] In one specific embodiment, the structure of the liquefied hydrocarbon storage tank is as follows: Figure 2 As shown. The storage tank includes: an inner tank 14, the main liquid container, made of cryogenic steel; an outer tank 15, the secondary liquid container, also made of cryogenic steel; a ceiling 20; an annular space 22; a sealing port 19; a steel tank top 21; a tank bottom insulation layer 16; a foundation 17; and a foundation heating system 18. The annular space is filled with insulation material, and the upper outer wall of the ceiling is also covered with an insulation layer.

[0037] In one specific embodiment, the structure of the liquefied hydrocarbon storage tank is as follows: Figure 3 As shown. The storage tank includes: an inner tank 14, the main liquid container, made of cryogenic steel; an outer tank 15, the secondary liquid container, made of prestressed concrete; a suspended ceiling 20; an annular space 22; a sealing port 19; a concrete tank top 25; a tank bottom insulation layer 16; a foundation 17; a foundation heating system 18; a thermal corner protection system 23; and a steam container 24 is provided on the side wall of the outer tank. The first end of the steam container is located in the annular space, and the second section extends along the side wall of the outer tank to the bottom into the tank bottom insulation layer.

[0038] In the above embodiments, Figure 2 and Figure 3 The liquefied hydrocarbon storage tank provided is a conventional device in the field, and the connection positions and connection methods between different components are also conventional in the field.

[0039] In one embodiment, the sealing port 8 is formed as an annular opening between the top of the side wall of the inner tank 1 and the ceiling 4; and the sealing port 8 allows gas to flow between the inner tank 1 and the annular space 3 under gas pressure; a ceiling space is formed between the ceiling 4 and the top of the liquefied hydrocarbon storage tank.

[0040] The method includes:

[0041] The first portion of nitrogen gas is introduced into the top of the annular space 3 via the gas curtain coil 5 to form the nitrogen gas curtain. The gas curtain coil 5 is disposed at the top of the annular space 3 and surrounds the inner tank 1. The tube wall of the gas curtain coil 5 forms an annular gas outlet, and the gas outlet of the gas curtain coil 5 faces the ceiling space. This disclosure provides a gas curtain coil that can form a nitrogen gas curtain outside the sealing port, thereby preventing hydrocarbon-containing gases from escaping into the annular space from the inner tank.

[0042] In one embodiment, the sealing port 8 of the liquefied hydrocarbon storage tank of this disclosure is formed as an annular opening around the top of the side wall of the inner tank 1, and a sealing material is provided between the annular opening and the ceiling 4 above the inner tank 1, so that the sealing port 8 allows gas to flow between the inner tank 1 and the annular space 3 under air pressure. The sealing material is a combination of an aluminum plate sealing ring and a sealing and insulating material, wherein the sealing and insulating material is disposed on the outer wall of the aluminum plate sealing ring. The sealing and insulating material can be a conventionally selected insulating material in the art.

[0043] This disclosure uses a sealing material to seal the connection between the annular opening of the inner tank and the ceiling, which allows the gas in the inner tank and the annular space to circulate under air pressure, thereby achieving the functions of nitrogen purging and drying of the storage tank and preventing condensation, thus improving the safety of the liquefied hydrocarbon storage tank.

[0044] In one specific embodiment, the sealing material may further include fiberglass mat material. This is used to prevent the sealing effect from being reduced due to possible displacement of the suspended ceiling. Specifically, the fiberglass mat can be installed in a manner conventionally chosen in the art, for example, it can be attached to the gap at the connection between the aluminum plate sealing ring and the suspended ceiling to further improve the sealing effect.

[0045] In a preferred embodiment, the total nitrogen flow rate at the gas outlet of the gas curtain coil 5 is controlled within a reasonable range to ensure pressure balance in all parts of the storage tank, and the pressure at the gas outlet is positive. For example, the total nitrogen flow rate at the gas outlet of the gas curtain coil 5 is 500–1500 Nm³. 3 / hr can also be adjusted according to the actual situation.

[0046] In one embodiment, the method for storing cryogenic liquefied hydrocarbons further includes: introducing a second portion of nitrogen gas into the bottom of the annular space 3 via an annular purge pipe 6. The annular purge pipe 6 is located at the bottom of the annular space 3 and surrounds the inner tank 1. The pipe wall of the annular purge pipe 6 forms an annular first opening, with the first opening of the annular purge pipe 6 facing the top of the annular space 3. In this embodiment, when the liquefied hydrocarbon storage tank is in normal use, nitrogen gas is introduced from outside the tank into the annular space through the annular purge pipe. This not only allows for the reuse of the annular purge pipe, avoiding the waste of equipment resources caused by the "disposable" use of the annular purge pipe (which is only used for drying and purging before start-up); but also allows nitrogen gas to be introduced into the bottom of the annular space via the annular purge pipe and purged towards the top, so that the hydrocarbon-containing gas in the annular space is gradually introduced back into the inner tank under the action of nitrogen, achieving an anti-condensation effect.

[0047] In a preferred embodiment, the total nitrogen flow rate at the gas outlet of the annular purge pipe 6 is controlled within a reasonable range to ensure pressure balance in all parts of the storage tank, and the pressure at the gas outlet is positive. For example, the total nitrogen flow rate at the gas outlet of the annular purge pipe 6 is 500–1500 Nm³. 3 / hr can also be adjusted according to the actual situation.

[0048] In one implementation, the method includes:

[0049] When the pressure in the annular space 3 is lower than the first preset pressure, a first portion of nitrogen gas is introduced into the top of the annular space 3, and a second portion of nitrogen gas is introduced into the bottom of the annular space 3.

[0050] Optionally, the first preset pressure is the warning pressure value that causes negative pressure in the liquefied hydrocarbon storage tank under local winter conditions when the liquefied hydrocarbon storage tank is used; the first preset pressure can be adjusted according to the actual situation, for example, 0.9 to 1.1 kPag.

[0051] When the pressure in the annular space 3 reaches the second preset pressure, the introduction of nitrogen into the top and bottom of the annular space 3 is stopped.

[0052] Optionally, the second preset pressure is the minimum pressure value at which the liquefied hydrocarbon storage tank maintains stability, and can be adjusted according to actual conditions, for example, 3 to 5 kPag.

[0053] This disclosure uses the pressure within the annular space as a criterion for introducing or stopping nitrogen gas during application, which can prevent excessively high partial pressure of hydrocarbon gases within the annular space, prevent hydrocarbon-containing gases from condensing at low temperatures, and improve the safety of the storage tank.

[0054] In one embodiment, the method for storing cryogenic liquefied hydrocarbons further includes, before storing the liquefied hydrocarbons in the inner tank 1 of the liquefied hydrocarbon storage tank:

[0055] The inner tank 1, annular space 3, and bottom insulation layer 12 of the liquefied hydrocarbon storage tank are purged sequentially with nitrogen gas to displace the air within these components. In this embodiment, using nitrogen to purge and dry the liquefied hydrocarbon storage tank avoids residual air in the tank and improves storage efficiency.

[0056] In one specific embodiment, a third portion of nitrogen gas is used to sequentially purge the inner tank 1, the annular space 3, and the bottom insulation layer 12 of the liquefied hydrocarbon storage tank, including:

[0057] The third part of nitrogen gas is introduced into the bottom of the inner tank 1 through the inner tank purging pipe 7, and the tank top air outlet 9 set on the top wall of the outer tank 2 is opened so that the air in the inner tank 1 escapes from the sealing port 8 into the annular space 3 and is discharged from the tank top air outlet 9.

[0058] Close the air outlet 9 at the top of the tank and open the second valve on the second branch pipe that connects the annular gap purge pipe 6 to the atmosphere, so that the third part of nitrogen gas is introduced into the bottom of the inner tank 1 through the inner tank purge pipe 7 and escapes from the sealing port 8 into the annular gap space 3, so that the air in the annular gap space 3 enters the annular gap purge pipe 6 and is discharged from the second branch pipe.

[0059] Close the second valve and open the pipeline valve connecting the first purge pipe 10 and the second purge pipe 11 at the bottom of the tank. This allows the third portion of nitrogen gas to be introduced into the bottom of the inner tank 1 through the inner tank purge pipe 7 and escape through the sealed port into the annular space 3. The nitrogen gas in the annular space 3 then enters the second purge pipe 11 at the bottom of the tank and returns to the first purge pipe 10 at the bottom of the tank via the connecting pipeline. It then enters the bottom insulation layer 12 at the bottom of the tank through the first purge pipe 10 at the bottom of the tank. The air in the bottom insulation layer at the bottom of the tank is then discharged through the bottom air exhaust pipe 13.

[0060] This invention continuously introduces nitrogen into the inner tank through an inner tank purging pipeline and opens different pipeline valves at different stages to allow air to be discharged through different pipelines, which can further improve the air replacement effect.

[0061] like Figure 1 As shown, a second aspect of this disclosure provides a system for storing liquefied hydrocarbons, the system comprising: a liquefied hydrocarbon storage tank, a gas curtain coil 5, and an annular purge pipe 6;

[0062] The liquefied hydrocarbon storage tank includes an inner tank 1, an outer tank 2, an annular space 3, a ceiling 4, and a sealing port 8, and the annular space 3 is filled with cold insulation material.

[0063] The annular space 3 is formed by a gap between the side wall of the inner tank 1 and the side wall of the outer tank 2;

[0064] The suspended ceiling 4 and the top of the liquefied hydrocarbon storage tank are separated to form a suspended ceiling space;

[0065] The suspended ceiling 4 is located above the inner tank 1 and has a gap. The top of the side wall of the inner tank has an annular opening. The annular opening is sealed with the suspended ceiling 4 to form the sealing port 8, so that the gas in the inner tank 1 and the annular space 3 can only flow through the sealing port 8.

[0066] The annular purge pipe 6 is formed as an annular pipe located at the bottom of the annular space 3 and surrounding the inner tank 1; the pipe wall of the annular purge pipe 6 has an annular first opening, and the first opening of the annular purge pipe 6 faces the top of the annular space 3; the annular purge pipe 6 also has a second opening extending to the outside of the liquefied hydrocarbon storage tank for communication with a nitrogen gas source or the atmosphere.

[0067] The gas curtain coil 5 is formed as an annular pipe located at the top of the annular space 3 and surrounding the inner tank 1. The pipe wall of the gas curtain coil 5 has an annular gas outlet, and the gas outlet of the gas curtain coil 5 faces the ceiling space. The gas curtain coil 5 also has a gas inlet extending to the outside of the liquefied hydrocarbon storage tank for communication with a nitrogen gas source.

[0068] The system for storing liquefied hydrocarbons disclosed herein has a first opening of the annular purging pipe located at the bottom of the annular space, and a second opening connected to the atmosphere or a nitrogen source outside the storage tank. This system can be used not only for purging and drying the air inside the pipe before the storage tank is started, but also for introducing nitrogen into the bottom of the annular space during normal use of the storage tank. This allows the hydrocarbon-containing gas in the annular space to be blown from the bottom to the top and introduced into the inner tank through the sealed port, achieving an anti-condensation effect and avoiding waste of equipment resources. At the same time, this disclosure also includes a gas curtain coil installed outside the sealed port, which can form a nitrogen gas curtain around the sealed port and facing the ceiling space within the annular space, preventing hydrocarbon-containing gas from the inner tank and above the ceiling from entering the annular space, ensuring that the hydrocarbon-containing gas content in the annular space is below a safe value, and guaranteeing the safety of the storage tank.

[0069] In one implementation, such as Figure 1 As shown, the second opening of the annular purging pipe 6 is connected to a first branch pipe and a second branch pipe. The first branch pipe is connected to a nitrogen gas source, and the second branch pipe is connected to the atmosphere. A first valve 26 is provided on the first branch pipe, and a second valve 27 is provided on the second branch pipe.

[0070] The system for storing liquefied hydrocarbons has both a start-up purging state and an anti-condensation state.

[0071] In the purging operation state, close the first valve 26 on the first branch pipe and open the second valve 27 on the second branch pipe to connect the annular purging pipe 6 with the atmosphere in order to discharge the air in the annular space 3.

[0072] In the anti-condensation working state, the first valve 26 on the first branch pipe is opened, and the second valve 27 on the second branch pipe is closed, so that the annular gap purge pipe 6 is connected to the nitrogen gas source to introduce nitrogen into the annular gap space 3. In this embodiment, when in the start-up purge working state, air in the annular gap space can be introduced into the first opening of the annular gap purge pipe and discharged to the atmosphere through the first branch pipe via the annular gap purge pipe; in the anti-condensation working state, nitrogen can be introduced through the second branch pipe and introduced in the opposite direction to the bottom of the annular gap space via the annular gap purge pipe, and the nitrogen is purged from the bottom to the top to increase the nitrogen partial pressure in the annular gap space and achieve the purpose of anti-condensation.

[0073] In a preferred embodiment, the system for storing liquefied hydrocarbons provided in this disclosure can be equipped with multiple annular space purge pipes 6. Each annular space purge pipe 6 has a second opening extending outside the liquefied hydrocarbon storage tank for communication with a nitrogen source or the atmosphere. A first valve is provided on the branch pipe of each annular space purge pipe communicating with the atmosphere, and a second valve is provided on the branch pipe of each annular space purge pipe communicating with the nitrogen source. Optionally, the second openings of the multiple annular space purge pipes can be symmetrically arranged around the vertical central axis of the liquefied hydrocarbon storage tank.

[0074] In a preferred embodiment, the system for storing liquefied hydrocarbons provided in this disclosure can be equipped with multiple gas curtain coils, each gas curtain coil having a gas inlet extending outside the liquefied hydrocarbon storage tank for communication with a nitrogen gas source. Optionally, the gas inlets of the multiple gas curtain coils can be symmetrically arranged around the vertical central axis of the liquefied hydrocarbon storage tank.

[0075] In a preferred embodiment, the gas curtain coil is positioned close to the side wall of the inner tank, which can further enhance the effect of the nitrogen gas curtain in preventing hydrocarbon-containing gases from escaping into the annular space.

[0076] In one embodiment, the system for storing liquefied hydrocarbons further includes an inner tank purging pipe 7, a first tank bottom purging pipe 10, a second tank bottom purging pipe 12, and a tank bottom air exhaust pipe 13; the top wall of the outer tank is provided with a tank top air outlet 9 for communicating with the atmosphere.

[0077] The liquefied hydrocarbon storage tank also includes a tank bottom insulation layer 12 disposed between the bottom wall of the inner tank 1 and the bottom wall of the outer tank 2;

[0078] The gas inlet of the inner tank purging pipe 7 is located outside the liquefied hydrocarbon storage tank and is used to connect with the nitrogen gas source; the gas outlet of the inner tank purging pipe 7 passes through the top wall and ceiling 4 of the outer tank 2 and extends to the bottom of the inner tank 1.

[0079] The first end of the second purging pipe 11 at the bottom of the tank is located at the top of the annular space 3, and the second end of the second purging pipe 11 at the bottom of the tank passes through the top wall of the outer tank 2 and extends to the outside of the liquefied hydrocarbon storage tank.

[0080] The first end of the first purging pipe 10 at the bottom of the tank is located outside the liquefied hydrocarbon storage tank and is connected to the second end of the second purging pipe 11 in an openable and closable manner. The second end of the first purging pipe 10 at the bottom of the tank passes through the outer tank and the annular space along the axial direction and extends into the bottom insulation layer 12, so that the gas entering the second purging pipe 11 at the bottom of the tank through the annular space 3 enters the bottom insulation layer 12 at the bottom of the tank through the first purging pipe 10 at the bottom of the tank.

[0081] The first end of the bottom air exhaust pipe 13 is disposed in the bottom insulation layer 12 to form a gas inlet. There is a gap between the first end of the bottom air exhaust pipe 13 and the second end of the bottom first purging pipe 10. The second end of the bottom air exhaust pipe 13 passes through the annular space 3 and the top wall of the outer tank 2 in sequence to form a gas outlet communicating with the atmosphere. In this embodiment, the inner tank, annular space and bottom insulation layer of the storage tank can also be purged and dried to exhaust air out of the storage tank.

[0082] In one specific embodiment, the sealing port 8 is provided with a sealing material, which is a combination of an aluminum plate sealing ring and a sealing and cold-insulating material, and the sealing and cold-insulating material is disposed on the outer wall of the sealing ring; optionally, it may also include fiberglass mat to avoid the reduction of sealing effect caused by possible displacement of the suspended ceiling. The fiberglass mat is a material well known in the art.

[0083] In one specific implementation, such as Figure 1 As shown, the system for storing liquefied hydrocarbons provided in this disclosure includes a liquefied hydrocarbon storage tank, a gas curtain coil 5, and an annular purge pipe 6;

[0084] The liquefied hydrocarbon storage tank includes an inner tank 1, an outer tank 2, an annular space 3, a ceiling 4, and a sealing port 8, and the annular space 3 is filled with cold insulation material.

[0085] An annular space 3 is formed between the side wall of the inner tank 1 and the side wall of the outer tank 2;

[0086] There is a gap between the suspended ceiling 4 and the top of the liquefied hydrocarbon storage tank to form a suspended ceiling space;

[0087] The ceiling 4 is located above the inner tank 1 and has a gap. The top of the side wall of the inner tank has an annular opening. The annular opening and the ceiling 4 are sealed to form a sealing port 8, so that the gas in the inner tank 1 and the annular space 3 can only flow through the sealing port 8.

[0088] The annular purge pipe 6 is formed as an annular pipe located at the bottom of the annular space 3 and surrounding the inner tank 1; the pipe wall of the annular purge pipe 6 has an annular first opening, and the first opening of the annular purge pipe 6 faces the top of the annular space 3; the annular purge pipe 6 also has a second opening extending to the outside of the liquefied hydrocarbon storage tank for communication with a nitrogen gas source or the atmosphere.

[0089] The gas curtain coil 5 is formed as an annular pipe located at the top of the annular space 3 and surrounding the inner tank 1. The pipe wall of the gas curtain coil 5 has an annular gas outlet, and the gas outlet of the gas curtain coil 5 faces the ceiling space. The gas curtain coil 5 also has a gas inlet extending to the outside of the liquefied hydrocarbon storage tank for communication with a nitrogen gas source.

[0090] The second opening of the annular purging pipe 6 is connected to a first branch pipe and a second branch pipe. The first branch pipe is connected to a nitrogen gas source, and the second branch pipe is connected to the atmosphere. A first valve 26 is provided on the first branch pipe, and a second valve 27 is provided on the second branch pipe.

[0091] The system also includes an inner tank purging pipe 7, a first tank bottom purging pipe 10, a second tank bottom purging pipe 12, and a tank bottom air exhaust pipe 13; the top wall of the outer tank is provided with a tank top air outlet 9 for communication with the atmosphere;

[0092] The liquefied hydrocarbon storage tank also includes a tank bottom insulation layer 12 disposed between the bottom walls of the inner tank and the outer tank;

[0093] The gas inlet of the inner tank purging pipe 7 is located outside the liquefied hydrocarbon storage tank and is used to connect with the nitrogen gas source; the gas outlet of the inner tank purging pipe 7 passes through the top wall and ceiling 4 of the outer tank 2 and extends to the bottom of the inner tank 1.

[0094] The first end of the second purging pipe 11 at the bottom of the tank is located at the top of the annular space 3, and the second end of the second purging pipe 11 at the bottom of the tank passes through the top wall of the outer tank 2 and extends to the outside of the liquefied hydrocarbon storage tank.

[0095] The first end of the first purging pipe 10 at the bottom of the tank is located outside the liquefied hydrocarbon storage tank and is connected to the second end of the second purging pipe 11 in an openable and closable manner. The second end of the first purging pipe 10 at the bottom of the tank passes through the outer tank and the annular space along the axial direction and extends into the bottom insulation layer 12, so that the gas entering the second purging pipe 11 at the bottom of the tank through the annular space 3 enters the bottom insulation layer 12 at the bottom of the tank through the first purging pipe 10 at the bottom of the tank.

[0096] The first end of the bottom air exhaust pipe 13 is disposed on the bottom insulation layer 12 to form a gas inlet. There is a gap between the first end of the bottom air exhaust pipe 13 and the second end of the bottom first purging pipe 10. The second end of the bottom air exhaust pipe 13 passes through the annular space 3 and the top wall of the outer tank 2 in sequence to form a gas outlet communicating with the atmosphere.

[0097] The sealing port 8 is provided with a sealing material, which is a combination of an aluminum plate sealing ring and a sealing and cold insulation material, and the sealing and cold insulation material is provided on the outer wall of the sealing ring; optionally, the sealing material also includes fiberglass mat.

[0098] In one specific implementation, the following is adopted: Figure 1The specific working process and principle of the system for storing liquefied hydrocarbons shown include:

[0099] 1. Initial cleaning and purging phase:

[0100] --Before the liquefied hydrocarbon storage tank is put into use for the first time, open the valve of the pipeline connected to the port of the inner tank purging pipe 7, introduce nitrogen into the bottom of the inner tank 1, and purge the air in the inner tank from the bottom to the top of the inner tank. Under the purging action of nitrogen, the air in the inner tank 1 escapes from the sealing port 8 at the top of the inner tank side wall into the annular space 3, and then enters the dome space between the top wall of the outer tank and the ceiling 4, and is discharged to the atmosphere through the tank top air outlet 9 on the top wall of the outer tank.

[0101] --When the water dew point and oxygen content of the inner tank reach the standard: water dew point <10℃, oxygen content <8% (or the standard value is set according to the actual situation), the pipeline valve of the inner tank purge pipe 7 is closed, the second valve 27 of the second branch of the annular purge pipe 6 is opened, and the first valve of the first branch is closed; and nitrogen is introduced into the inner tank 1 through the inner tank purge pipe 7. The nitrogen in the inner tank 1 enters the top of the annular space 3 through the sealing port 8. Under the pressure of the nitrogen, the air in the annular space 3 enters the annular purge pipe 6 at the bottom of the annular space and is discharged into the atmosphere through the second branch pipe 27 of the annular purge pipe 6.

[0102] --When the dew point and oxygen content of the annular space 3 reach the standard: dew point <10℃, oxygen content <8% (or set the standard value according to the actual situation), close the second valve 27 of the second branch pipe and open the valve on the connecting pipeline between the first purging pipeline 10 and the second purging pipeline 11 at the bottom of the tank; and continue to introduce nitrogen into the inner tank 1 through the inner tank purging pipeline 7. The nitrogen in the inner tank 1 enters the top of the annular space 3 through the sealing port 8. The nitrogen enters the second purging pipeline 11 at the bottom of the tank, and then returns to the first purging pipeline 10 at the bottom of the tank through the connecting pipeline. Then it enters the bottom insulation layer 12 at the bottom of the tank through the first purging pipeline 10 at the bottom of the tank to purge the air in the bottom insulation layer 12. The air in the bottom insulation layer at the bottom of the tank is discharged through the bottom air discharge pipe 13.

[0103] --When the water dew point and oxygen content of the tank bottom insulation layer 12 reach the standard, specifically: water dew point <10℃, oxygen content <8% (or set the standard value according to the actual situation), close the valve of the pipeline connected to the inner tank purge pipeline 7, close the valve on the pipeline connected to the first purge pipeline 10 and the second purge pipeline 11 at the bottom of the tank, and close the valve on the air exhaust pipe 13 at the bottom of the tank.

[0104] The above steps can remove air from the tank, annular space, and bottom insulation layer of the liquefied hydrocarbon storage tank before it is put into use, so that it can be used for subsequent storage of liquefied hydrocarbons.

[0105] 2. Anti-condensation stage:

[0106] --The liquefied hydrocarbons are stored in the inner tank 1 of the liquefied hydrocarbon storage tank. When the pressure in the annular space is lower than the first preset pressure, the first valve 26 on the first branch pipe connected to the annular purge pipe 6 is opened, and nitrogen gas is introduced into the bottom of the annular space 3 through the annular purge pipe 6. The nitrogen gas is blown from the air hole on the annular purge pipe 6 toward the top of the annular space, so that the hydrocarbon-containing gas in the annular space 3 gradually enters the inner tank 1 from the sealing port 8 at the top of the side wall of the inner tank 1.

[0107] --In addition, open the valve of the pipeline connecting the air curtain coil 5 and the nitrogen source to introduce nitrogen into the top of the annular space 3. The nitrogen is blown towards the bottom of the ceiling space through the air hole of the nitrogen coil 5, forming a nitrogen air curtain outside the sealing port 8.

[0108] --When the pressure in the annular space is higher than the stable operating pressure of the storage tank, close the first valve 26 of the first branch of the annular purge pipe 6, close the valve on the pipeline connecting the gas curtain coil 5 and the nitrogen source, and stop the supply of nitrogen.

[0109] The system structure used in the above specific embodiments has been described in detail in the foregoing content, and belongs to the same inventive concept as the technical solution provided in the foregoing content, so it will not be repeated here.

[0110] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0111] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0112] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for storing liquefied hydrocarbons, characterized in that, The method includes the following steps: The liquefied hydrocarbons are stored in the inner tank (1) of the liquefied hydrocarbon storage tank, and the top of the side wall of the inner tank (1) is provided with a sealing port (8). A first portion of nitrogen gas is introduced into the top of the annular space (3) located outside the inner tank (1) to form a nitrogen gas curtain outside the sealing port (8) of the inner tank; a second portion of nitrogen gas is introduced into the bottom of the annular space (3) so that the hydrocarbon-containing gas in the annular space (3) returns to the inner tank (1) through the sealing port (8); The sealing port (8) is formed as an annular opening between the top of the side wall of the inner tank (1) and the ceiling (4); and the sealing port (8) allows gas to flow between the inner tank (1) and the annular space (3) under gas pressure; a ceiling space is formed between the ceiling (4) and the top of the liquefied hydrocarbon storage tank; the method includes: The first portion of nitrogen gas is introduced into the top of the annular space (3) via the gas curtain coil (5) to form the nitrogen gas curtain; the gas curtain coil (5) is located at the top of the annular space (3) and surrounds the inner tank (1), and the pipe wall of the gas curtain coil (5) forms an annular gas outlet, and the gas outlet of the gas curtain coil (5) faces the ceiling space. The second portion of nitrogen gas is introduced into the bottom of the annular space (3) via the annular purge pipe (6). The annular purge pipe (6) is located at the bottom of the annular space (3) and surrounds the inner tank (1). The pipe wall of the annular purge pipe (6) has an annular first opening, and the first opening of the annular purge pipe (6) faces the top of the annular space (3).

2. The method according to claim 1, characterized in that, The sealing opening (8) is provided with a combination material including an aluminum plate sealing ring and a sealing and cold insulation material on the outside. The sealing and cold insulation material is provided on the outer wall of the aluminum plate sealing ring. The sealing opening material also includes glass fiber felt. The pressure at the gas outlet of the air curtain coil (5) is positive.

3. The method according to claim 1, characterized in that, The pressure at the gas outlet of the annular purging pipe (6) is positive.

4. The method according to claim 1, characterized in that, The method includes: When the pressure in the annular space (3) is lower than the first preset pressure, a first portion of nitrogen is introduced into the top of the annular space (3), and a second portion of nitrogen is introduced into the bottom of the annular space (3). The first preset pressure is the warning pressure value that causes negative pressure in the liquefied hydrocarbon storage tank under local winter conditions when the liquefied hydrocarbon storage tank is used; When the pressure in the annular space (3) reaches the second preset pressure, the introduction of nitrogen into the top and bottom of the annular space (3) is stopped; The second preset pressure is the minimum pressure value at which the liquefied hydrocarbon storage tank maintains stability.

5. The method according to claim 1, characterized in that, Before storing liquefied hydrocarbons in the inner tank (1) of the liquefied hydrocarbon storage tank, the method further includes: The inner tank (1), the annular space (3) and the bottom insulation layer (12) of the liquefied hydrocarbon storage tank are purged with nitrogen in sequence using a third part of nitrogen to displace the air in the inner tank (1), the annular space (3) and the bottom insulation layer (12).

6. The method according to claim 5, characterized in that, The process of purging the inner tank (1), the annular space (3), and the bottom insulation layer (12) of the liquefied hydrocarbon storage tank with nitrogen gas in sequence includes: The third part of nitrogen gas is introduced into the bottom of the inner tank (1) through the inner tank purging pipe (7), and the tank top air outlet (9) set on the top wall of the outer tank (2) is opened so that the air in the inner tank (1) escapes from the sealing port (8) into the annular space (3) and is discharged from the tank top air outlet (9). Close the air outlet (9) at the top of the tank and open the second valve on the second branch pipe that connects the annular gap purge pipe (6) to the atmosphere, so that the third part of nitrogen gas is introduced into the bottom of the inner tank (1) through the inner tank purge pipe (7) and escapes from the sealing port (8) into the annular gap space (3), so that the air in the annular gap space (3) enters the annular gap purge pipe (6) and is discharged from the second branch pipe; Close the second valve and open the pipeline valve connecting the first purge pipe (10) and the second purge pipe (11) at the bottom of the tank. This allows the third part of nitrogen to be introduced into the bottom of the inner tank (1) through the inner tank purge pipe (7) and escape from the sealed port into the annular space (3). The nitrogen in the annular space (3) enters the second purge pipe (11) at the bottom of the tank and returns to the first purge pipe (10) at the bottom of the tank through the connecting pipeline. It then enters the bottom insulation layer (12) at the bottom of the tank through the first purge pipe (10) at the bottom of the tank. The air in the bottom insulation layer at the bottom of the tank is then discharged through the bottom air exhaust pipe (13).

7. A system for storing liquefied hydrocarbons, characterized in that, The system includes: a liquefied hydrocarbon storage tank, a gas curtain coil (5), and an annular purging pipe (6); The liquefied hydrocarbon storage tank includes an inner tank (1), an outer tank (2), an annular space (3), a ceiling (4), and a sealing port (8), and the annular space (3) is filled with cold insulation material; The annular space (3) is formed by the gap between the side wall of the inner tank (1) and the side wall of the outer tank (2). The suspended ceiling (4) and the top of the liquefied hydrocarbon storage tank are separated to form a suspended ceiling space; The ceiling (4) is located above the inner tank (1) and has a gap. The top of the side wall of the inner tank has an annular opening. The annular opening is sealed with the ceiling (4) to form the sealing port (8) so that the gas in the inner tank (1) and the annular space (3) can only flow through the sealing port (8). The annular purge pipe (6) is formed as an annular pipe located at the bottom of the annular space (3) and surrounding the inner tank (1); the pipe wall of the annular purge pipe (6) has an annular first opening, and the first opening of the annular purge pipe (6) faces the top of the annular space (3); the annular purge pipe (6) also has a second opening extending to the outside of the liquefied hydrocarbon storage tank for communication with a nitrogen gas source or the atmosphere; The gas curtain coil (5) is formed as an annular pipe located at the top of the annular space (3) and surrounding the inner tank (1). The pipe wall of the gas curtain coil (5) has an annular gas outlet, and the gas outlet of the gas curtain coil (5) faces the ceiling space. The gas curtain coil (5) also has a gas inlet extending to the outside of the liquefied hydrocarbon storage tank for communication with a nitrogen gas source.

8. The system according to claim 7, characterized in that, The second opening of the annular purging pipe (6) is connected to a first branch pipe and a second branch pipe. The first branch pipe is connected to a nitrogen gas source, and the second branch pipe is connected to the atmosphere. A first valve (26) is provided on the first branch pipe, and a second valve (27) is provided on the second branch pipe.

9. The system according to claim 8, characterized in that, The system has both a start-up purging state and an anti-condensation state. In the working state of the purging operation, the first valve on the first branch pipe is closed and the second valve on the second branch pipe is opened to connect the annular purging pipe (6) with the atmosphere so as to discharge the air in the annular space (3); In the anti-condensation working state; open the first valve on the first branch pipe and close the second valve on the second branch pipe to connect the annular gap purge pipe (6) with the nitrogen gas source, so as to introduce nitrogen into the annular gap space (3).

10. The system according to claim 7, characterized in that, The system also includes an inner tank purging pipe (7), a first tank bottom purging pipe (10), a second tank bottom purging pipe (12), and a tank bottom air exhaust pipe (13); the top wall of the outer tank is provided with a tank top air outlet (9) for communicating with the atmosphere; The liquefied hydrocarbon storage tank also includes a tank bottom insulation layer (12) disposed between the bottom walls of the inner tank and the outer tank. The gas inlet of the inner tank purging pipe (7) is located outside the liquefied hydrocarbon storage tank and is used to connect with a nitrogen gas source; the gas outlet of the inner tank purging pipe (7) passes through the top wall of the outer tank (2) and the ceiling (4) in sequence and extends to the bottom of the inner tank (1); The first end of the second purging pipe (11) at the bottom of the tank is located at the top of the annular space (3), and the second end of the second purging pipe (11) at the bottom of the tank passes through the top wall of the outer tank (2) and extends to the outside of the liquefied hydrocarbon storage tank. The first end of the first purging pipe (10) at the bottom of the tank is located outside the liquefied hydrocarbon storage tank and is connected to the second end of the second purging pipe (11) in an openable and closable manner. The second end of the first purging pipe (10) at the bottom of the tank passes through the outer tank and the annular space along the axial direction and extends into the bottom insulation layer (12) of the tank, so that the gas entering the second purging pipe (11) at the bottom of the tank from the annular space (3) enters the bottom insulation layer (12) of the tank through the first purging pipe (10) at the bottom of the tank. The first end of the bottom air exhaust pipe (13) is disposed on the bottom insulation layer (12) to form a gas inlet. There is a gap between the first end of the bottom air exhaust pipe (13) and the second end of the bottom first purge pipe (10). The second end of the bottom air exhaust pipe (13) passes through the annular space (3) and the top wall of the outer tank (2) in sequence to form a gas outlet communicating with the atmosphere. The sealing port (8) is provided with a sealing material, which is a combination of an aluminum plate sealing ring and a sealing and cold insulation material. The sealing and cold insulation material is provided on the outer wall of the sealing ring; the sealing material also includes glass fiber felt.

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