Liquid nitrogen gasification system for purging large low-temperature storage tank

Abstract

The utility model provides a liquid nitrogen gasification system for purging a large low-temperature storage tank, which comprises a nitrogen conveying pipeline capable of being connected with a liquid outlet of a liquid nitrogen tank car and a nitrogen purging pipeline used for purging the low-temperature storage tank, and a control valve is arranged at the outlet end of the nitrogen conveying pipeline. The outlet end of the nitrogen purging pipeline is provided with a root valve located at the root of a purging opening of the low-temperature storage tank. The device is characterized in that an air temperature type vaporizer is arranged on the nitrogen conveying pipeline, and an electric tracing band is wound outside the section, close to the root valve, of the nitrogen purging pipeline. According to the utility model, the purchase cost of the electric tracing band is far lower than that of an electric heating water bath vaporizer, and the electric tracing band is a common finished product material and can be quickly purchased by electromechanical markets and online e-commerce platforms across the country; and after purging is finished, the electric tracing band can be detached from the nitrogen purging pipeline, later maintenance is not needed, and manpower and material resources are saved.

Description

Technical Field

[0001] The utility model belongs to the technical field of cryogenic storage tanks, and in particular relates to a liquid nitrogen gasification system for purging a large cryogenic storage tank. Background Art

[0002] In the final stage of the construction of cryogenic storage tanks (such as LNG storage tanks), high-purity nitrogen is usually required to purge, dry and replace various areas inside the tank according to specifications and design requirements. The purge, drying and replacement of LNG storage tanks need to be carried out continuously until the water dew point and oxygen content of each discharge port meet the design and specification requirements. Therefore, nitrogen purging is a key step before pre-cooling and liquid filling of LNG storage tanks.

[0003] Due to the large LNG storage tanks (effective volume not less than 5000m 3 The storage tank has a large capacity and must meet the water dew point and oxygen content requirements of each part. The nitrogen purge cycle usually lasts for more than ten days or even dozens of days. There are usually two ways to obtain a long-term stable high-purity nitrogen source: one is to provide it through the factory's supporting air separation unit, nitrogen generator, etc.; the other is to purchase liquid nitrogen and transport it to the site by liquid nitrogen tank truck. The second method has fewer restrictions and is universal.

[0004] At normal pressure (101.325KPa), the boiling point of liquid nitrogen (LN) is -196.56℃, and 1 cubic meter of liquid nitrogen can be vaporized and expanded to 648 cubic meters of pure gaseous nitrogen (0℃). The higher the temperature, the more complete the vaporization of liquid nitrogen. To ensure the vaporization effect, according to its physical properties, after the liquid nitrogen is transported to the site, it cannot directly enter the nitrogen purge pipeline of the storage tank. Instead, a special vaporization device must be used first to control the liquid nitrogen to fully absorb heat and vaporize to meet the temperature and pressure requirements of the purge.

[0005] CN202020569555.9 discloses a multi-condition liquid nitrogen gasification device based on automatic temperature control, which fully gasifies the liquid nitrogen by connecting an electric heating water bath gasifier in series behind the air temperature gasifier. The electric heating water bath gasifier heats the water in the device through a thermal resistor, and uses water as a medium to transfer heat to the heat exchange coil in the device. The low-temperature nitrogen coming out of the air temperature gasifier enters the heat exchange coil of the electric heating water bath gasifier to absorb heat. However, the electric heating water bath gasifier has the following disadvantages:

[0006] 1) The one-time investment of the electric heating water bath vaporizer is high. Large LNG storage tanks are usually built all over the country, and the locations are remote and far away from the urban area. Therefore, if it is impossible to rent an electric heating water bath vaporizer that meets the requirements in time, the only option is to purchase the equipment directly. However, the purge of the LNG storage tank itself is a one-time work. After the purge is completed, the electric heating water bath vaporizer will basically be idle, and the input-output ratio is low.

[0007] 2) The maintenance cost of the electric heating water bath vaporizer is high. During the gasification and purging process, the pressure of the electric heating water bath vaporizer will reach 0.3-0.5MPa. It is a pressure vessel and is subject to the special equipment safety supervision of the provincial quality and technical supervision bureau. Therefore, the maintenance period requires additional manpower and material resources to meet the regulatory requirements, which increases management costs. Utility Model Content

[0008] The utility model aims to solve the technical problems existing in the prior art and provides a liquid nitrogen gasification system for purging a large cryogenic storage tank.

[0009] In order to achieve the above-mentioned purpose, the utility model adopts the following technical scheme: a liquid nitrogen gasification system for purging a large cryogenic storage tank, comprising a nitrogen delivery pipeline that can be connected to the liquid outlet of a liquid nitrogen tank truck, and a nitrogen purge pipeline for purging the cryogenic storage tank, a control valve is provided at the outlet end of the nitrogen delivery pipeline, and a root valve located at the root of the purge port of the cryogenic storage tank is provided at the outlet end of the nitrogen purge pipeline; it is characterized in that an air-temperature vaporizer is provided on the nitrogen delivery pipeline, and an electric heating belt is wound around the section of the nitrogen purge pipeline close to the root valve.

[0010] The above technical solution utilizes electric heating tape for supplementary heating to replace the traditional electric heating water bath vaporizer. The purchase cost of the electric heating tape is much lower than that of the electric heating water bath vaporizer. The electric heating tape is a commonly used finished material and can be quickly purchased in electromechanical markets and online e-commerce platforms across the country. Moreover, after the purge is completed, the electric heating tape can be removed from the nitrogen purge pipeline, without the need for subsequent maintenance, saving manpower and material resources.

[0011] In a preferred embodiment of the present utility model, a first pressure gauge and a first temperature gauge are provided on the nitrogen purge pipeline between the electric heating belt and the root valve.

[0012] In the above technical solution, the first pressure gauge is used to monitor the pressure index of the nitrogen after final gasification, and the first thermometer is used to monitor the temperature index of the nitrogen after final gasification. At the same time, the opening of the root valve is adjusted to maintain the first pressure gauge and the first thermometer at a stable value.

[0013] In a preferred embodiment of the present utility model, a second pressure gauge and a second temperature gauge are provided on the nitrogen delivery pipeline between the air-temperature gasifier and the control valve.

[0014] In the above technical solution, the second pressure gauge is used to monitor the pressure index of the nitrogen after being gasified by the air-temperature gasifier, and the second temperature gauge is used to monitor the temperature index of the nitrogen after being gasified by the air-temperature gasifier. At the same time, the opening of the control valve is adjusted to maintain the second pressure gauge and the second temperature gauge at a stable value.

[0015] In a preferred embodiment of the present invention, a stop valve is provided at the inlet end of the nitrogen purge pipeline; and / or the electric heating cable is coated with an insulation layer.

[0016] In the above technical solution, the stop valve is used to control the on-off of the nitrogen purge pipeline. Before purge, the stop valve and the root valve are opened to facilitate power-on and test the heating and temperature regulation functions of the electric heating tape. The insulation layer can make the heat generated by the electric heating tape more concentrated on the nitrogen purge pipeline to avoid dissipation into the air, thereby improving the heating efficiency.

[0017] In a preferred embodiment of the present invention, the thermal insulation layer is made of glass fiber wool.

[0018] In the above technical solution, the glass fiber wool has low cost and good thermal insulation performance.

[0019] In a preferred embodiment of the present invention, the length of the nitrogen purge pipeline is not less than 50 meters.

[0020] The above technical solution, based on the characteristic of the long distance from the ground to the tank top of the nitrogen purge pipeline of the large LNG storage tank, enables the low-temperature nitrogen flowing through the nitrogen purge pipeline to absorb the heat in the air for a second heating, and then use the electric heating tape to complete the third heating to achieve the same liquid nitrogen gasification effect. Compared with the use of an electric heating water bath vaporizer, the overall energy consumption is lower.

[0021] In another preferred embodiment of the present utility model, the liquid nitrogen gasification system also includes a controller, the controller includes a first comparator and a second comparator; the first input end of the first comparator is connected to the pressure analog signal output end of the first pressure gauge, the second input end of the first comparator is connected to the pressure low threshold memory, and the output end of the first comparator is connected to the first input end of the first OR gate; the first input end of the second comparator is connected to the temperature analog signal output end of the first temperature gauge, the second input end of the second comparator is connected to the temperature low threshold memory, and the output end of the second comparator is connected to the second input end of the first OR gate; the output end of the first OR gate is connected to the opening reduction control end of the root valve.

[0022] The above technical solution, by setting a first comparator, a second comparator, a low pressure threshold memory, and a low temperature threshold memory, automatically reduces the opening of the root valve when the first pressure gauge shows low pressure or the first temperature gauge shows low temperature, thereby extending the residence time of the low-temperature nitrogen in the last section of the nitrogen purge pipeline, continuously absorbing the heat generated by the electric heating tape, and increasing the temperature and pressure of the purge nitrogen.

[0023] In another preferred embodiment of the present utility model, the controller also includes a third comparator and a fourth comparator; the first input end of the third comparator is connected to the pressure analog signal output end of the first pressure gauge, the second input end of the third comparator is connected to the pressure high threshold memory, and the output end of the third comparator is connected to the first input end of the second OR gate; the first input end of the fourth comparator is connected to the temperature analog signal output end of the first temperature gauge, the second input end of the fourth comparator is connected to the temperature high threshold memory, and the output end of the second comparator is connected to the second input end of the second OR gate; the output end of the second OR gate is connected to the opening increase control end of the root valve.

[0024] The above technical solution, by setting a third comparator, a fourth comparator, a high pressure threshold memory, and a high temperature threshold memory, automatically increases the opening of the root valve when the first pressure gauge indicates high pressure or the first temperature gauge indicates high temperature, shortens the residence time of the low-temperature nitrogen in the last section of the nitrogen purge pipeline, and reduces the temperature and pressure of the purge nitrogen.

[0025] In another preferred embodiment of the present invention, a vertically arranged pipe rack supported on the ground is provided on the side of the cryogenic storage tank, a public pipe gallery supported on the ground is provided on the outside of the pipe rack, the upper end of the pipe rack is connected to a tank top operating platform located on the top of the cryogenic storage tank, and a nitrogen purge pipeline is laid to the tank top operating platform through the public pipe gallery and the pipe rack.

[0026] The above technical solution can be used for laying nitrogen purge pipelines by setting up a public pipe gallery, pipe racks and tank top operating platform, and the tank top operating platform can be used by staff to operate and inspect pipelines, control valves and instruments on the top of cryogenic storage tanks.

[0027] In another preferred embodiment of the present invention, the electric heating tape is wound around the outside of the nitrogen purge pipeline on the tank top operating platform.

[0028] In the above technical solution, before purging, the electric heating tape can be wound around the outside of the nitrogen purge pipeline through the tank top operating platform.

[0029] Compared with the prior art, the preferred technical solution of the utility model has the following beneficial effects:

[0030] 1) Low cost investment. The purchase cost of the electric heating cable of the utility model is much lower than that of the electric water bath vaporizer. The electric heating cable and the insulation layer are both commonly used finished products. The purchase can be completed quickly in the mechanical and electrical markets across the country and online e-commerce platforms.

[0031] 2) Save maintenance costs. After the purge is completed, the electric heating cable and the insulation layer are removed from the nitrogen purge pipeline, eliminating the need for subsequent maintenance, saving manpower and material resources.

[0032] 3) The heating temperature is controllable. By changing the heating length and winding density of the electric heating cable, or using a thermostat, the heating value of the electric heating cable can be flexibly controlled to cope with more complex environments.

[0033] 4) Energy saving. Based on the long distance from the ground to the tank top of the nitrogen purge pipeline attached to the large cryogenic storage tank, the utility model allows the low-temperature nitrogen flowing through the nitrogen purge pipeline to absorb the heat in the air for a second heating, and then uses the electric heating belt to complete the third heating, achieving the same liquid nitrogen gasification effect. Compared with the use of an electric water bath vaporizer, the overall energy consumption is lower.

[0034] 5) Save space. The auxiliary heating electric heating cable of the utility model is directly wound on the nitrogen purge pipeline, and there is no need to consider the installation position of the gasification equipment separately, which saves more space.

[0035] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0037] Figure 1 The present invention is a schematic structural diagram of a liquid nitrogen gasification system for purging a large cryogenic storage tank according to an embodiment.

[0038] Figure 2 yes Figure 1 Enlarged schematic diagram at point A in the middle.

[0039] The figure marks in the drawings of the specification include: stop valve 1, nitrogen purge pipeline 2, public pipeline gallery 3, pipe rack 4, first pressure gauge 5, first thermometer 6, root valve 7, tank top operating platform 8, cryogenic storage tank 9, liquid nitrogen tank truck 10, nitrogen transmission pipeline 11, control valve 12, air-temperature vaporizer 13, electric heating belt 14, insulation layer 15, second pressure gauge 16, second thermometer 17. DETAILED DESCRIPTION

[0040] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0041] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "vertical", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0042] In the description of the present utility model, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection of two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0043] The utility model provides a liquid nitrogen gasification system for purging large cryogenic storage tanks, such as Figure 1 and Figure 2 As shown, in a preferred embodiment, the liquid nitrogen gasification system includes a nitrogen delivery pipeline 11 that can be connected to the liquid outlet of the liquid nitrogen tank truck 10, and a nitrogen purge pipeline 2 for purging a cryogenic storage tank 9 (such as an LNG storage tank). A control valve 12 is provided at the outlet end of the nitrogen delivery pipeline 11, and a root valve 7 located at the root of the purge port of the cryogenic storage tank 9 is provided at the outlet end of the nitrogen purge pipeline 2. The root valve 7 is used to control the pressure and flow of the purge nitrogen and the opening and closing of the nitrogen purge port.

[0044] In the utility model, an air-temperature vaporizer 13 is provided on the nitrogen delivery pipeline 11, which is used to heat and vaporize the liquid nitrogen provided by the liquid nitrogen tank truck 10 into low-temperature nitrogen. The section of the nitrogen purge pipeline 2 close to the root valve 7 is wrapped with an electric heating belt 14, and a low-temperature self-limiting temperature electric heating belt 14 is used to maintain a maximum temperature of 65°C; preferably, the electric heating belt 14 is coated with an insulation layer 15, and the insulation layer 15 is made of glass fiber wool. Among them, the nitrogen purge pipeline 2 adopts a low-temperature resistant seamless steel pipe, which is used for purging, replacement and drying during the construction period and inspection and maintenance period of the low-temperature storage tank 9. The length of the nitrogen purge pipeline 2 is usually not less than 50 meters; preferably, the inlet end of the nitrogen purge pipeline 2 is provided with a stop valve 1, which is a low-temperature special valve for controlling the on and off of the nitrogen purge pipeline 2.

[0045] Preferably, a first pressure gauge 5 and a first thermometer 6 are provided on the nitrogen purge pipeline 2 between the electric heating tape 14 and the root valve 7. The first pressure gauge 5 is used to monitor the pressure index of the nitrogen after final gasification, and the first thermometer 6 is used to monitor the temperature index of the nitrogen after final gasification.

[0046] Further preferably, a second pressure gauge 16 and a second temperature gauge 17 are provided on the nitrogen delivery pipeline 11 between the air-temperature gasifier 13 and the control valve 12. The second pressure gauge 16 is used to monitor the pressure index of the nitrogen after gasification by the air-temperature gasifier 13, and the second temperature gauge 17 is used to monitor the temperature index of the nitrogen after gasification by the air-temperature gasifier 13.

[0047] In practice, the air-temperature vaporizer 13, the second pressure gauge 16, the second temperature gauge 17 and the control valve 12 can be made into a whole, and the nitrogen delivery pipeline 11 connected to the liquid nitrogen tank truck 10 adopts a stainless steel hose, and the nitrogen delivery pipeline 11 connected to the nitrogen purge pipeline 2 also adopts a stainless steel hose.

[0048] In the utility model, a vertically arranged pipe rack 4 supported on the ground is provided on the side of the cryogenic storage tank 9, and a public pipe gallery 3 supported on the ground is provided on the outside of the pipe rack 4. The upper end of the pipe rack 4 is connected to a tank top operating platform 8 located on the top of the cryogenic storage tank 9. The tank top operating platform 8 is used for the staff to operate and repair the pipelines, control valves 12 and instruments on the tank top of the cryogenic storage tank 9. People can climb to the tank top operating platform 8 through the pipe rack 4. The nitrogen purge pipeline 2 is laid to the tank top operating platform 8 through the public pipe gallery 3 and the pipe rack 4, and then connected to the purge port of the cryogenic storage tank 9. The electric heating belt 14 is wrapped around the nitrogen purge pipeline 2 on the tank top operating platform 8. The first pressure gauge 5, the first temperature gauge 6 and the root valve 7 are also located on the tank top operating platform 8, which is convenient for disassembly and maintenance.

[0049] After the low-temperature storage tank 9 complete set of equipment is completed, the low-temperature storage tank 9 is ready for purging, drying and replacement. Figure 1 As shown in the figure, the components of the liquid nitrogen gasification system are connected. Before the purge begins, close the control valve 12, open the stop valve 1 and the root valve 7, and evenly wrap the electric heating cable 14 around the nitrogen purge pipeline 2 on the tank top operating platform 8. Power on and test the heating and temperature regulation functions of the electric heating cable 14. After meeting the requirements, wrap a layer of insulation layer 15 around the outside of the heating cable.

[0050] At the beginning of the purge, the electric heating cable 14 is energized to heat the nitrogen purge pipeline 2. The liquid nitrogen tanker 10 controls the release of a small amount of liquid nitrogen (the control valve 12 is closed at this time), and enters the air-temperature vaporizer 13 through the nitrogen delivery pipeline 11. When the liquid nitrogen flows in the air-temperature vaporizer 13, it automatically absorbs the heat in the air through the heat exchange tubes and fins, and is initially vaporized into low-temperature nitrogen. When the pressure of the second pressure gauge 16 reaches a predetermined value, the control valve 12 is slowly opened to control the low-temperature nitrogen to enter the nitrogen purge pipeline 2. Adjust the opening of the control valve 12 to maintain the second pressure gauge 16 and the second temperature gauge 17 at a stable value.

[0051] Since the nitrogen purge pipeline 2 has a long path, similar to the "finless" air-temperature gasifier 13, while the low-temperature nitrogen flows in the nitrogen purge pipeline 2, the pipe wall of the nitrogen purge pipeline 2 can absorb heat in the air to achieve a second temperature increase.

[0052] The electric heating belt 14 is tightly wound around the end of the nitrogen purge pipeline 2, continuously heating the nitrogen purge pipeline 2, and the low-temperature nitrogen that has been heated twice flows through this section, absorbing the heat generated by the electric heating belt 14 to achieve a third heating. The electric heating belt 14 is coated with an insulation layer 15 on the outside, which can make the heat generated by the electric heating belt 14 more concentrated on the nitrogen purge pipeline 2 to avoid dissipation into the air, thereby improving the heating efficiency.

[0053] By adjusting the opening of the root valve 7, the temperature and pressure of the nitrogen before it finally enters the cryogenic storage tank 9 can be controlled. When the first pressure gauge 5 shows low pressure or the first thermometer 6 shows low temperature, the opening of the root valve 7 is reduced or the root valve 7 is closed, so that the low-temperature nitrogen in the nitrogen purge pipeline 2 cannot be discharged immediately, and its residence time at the end of the nitrogen purge pipeline 2 is extended, and the heat generated by the electric heating belt 14 is continuously absorbed. Nitrogen absorbs heat and expands, and the values ​​of the first pressure gauge 5 and the first thermometer 6 rise. When they reach the predetermined value range, the opening of the root valve 7 is slightly adjusted to increase the temperature and pressure to reduce overtemperature and overpressure. By adjusting the opening of the root valve 7 multiple times, the temperature and pressure of the nitrogen before entering the cryogenic storage tank 9 gradually tend to be stable within the predetermined range, meeting the requirements of long-term purge.

[0054] In the present utility model, the root valve 7 is a manual valve or an electric control valve. When the root valve 7 is a manual valve, the staff can manually adjust the opening of the root valve 7. When the root valve 7 is an electric valve, the opening of the root valve can be automatically adjusted by the controller.

[0055] Specifically, when the root valve 7 is an electric valve, the liquid nitrogen gasification system further includes a controller, which includes a first comparator and a second comparator; the first input end of the first comparator is connected to the pressure analog signal output end of the first pressure gauge 5 (specifically, it can be connected to the output signal end of the pressure sensor in the pressure gauge 5. In another preferred embodiment of the utility model, a pressure sensor such as WH131 or CBSA-5T can be arranged in the nitrogen purge pipeline), the second input end of the first comparator is connected to the pressure low threshold memory, and the output end of the first comparator is connected to the first input end of the first OR gate; the first input end of the second comparator is connected to the temperature analog signal output end of the first thermometer 6 (specifically, it can be connected to the output signal end of the temperature sensor in the thermometer 6. In another preferred embodiment of the utility model, a temperature sensor such as GWD10 or PT100 can be arranged in the nitrogen purge pipeline), the second input end of the second comparator is connected to the temperature low threshold memory, and the output end of the second comparator is connected to the second input end of the first OR gate; the output end of the first OR gate is connected to the opening reduction control end of the root valve 7.

[0056] Further preferably, the controller also includes a third comparator and a fourth comparator; the first input end of the third comparator is connected to the pressure analog signal output end of the first pressure gauge 5 (specifically, it can be connected to the output signal end of the pressure sensor in the pressure gauge 5. In another preferred embodiment of the utility model, a pressure sensor, such as WH131 or CBSA-5T, can be arranged in the nitrogen purge pipeline), the second input end of the third comparator is connected to the pressure high threshold memory, and the output end of the third comparator is connected to the first input end of the second OR gate; the first input end of the fourth comparator is connected to the temperature analog signal output end of the first thermometer 6 (specifically, it can be connected to the output signal end of the temperature sensor in the thermometer 6. In another preferred embodiment of the utility model, a temperature sensor, such as GWD10 or PT100, can be arranged in the nitrogen purge pipeline), the second input end of the fourth comparator is connected to the temperature high threshold memory, and the output end of the second comparator is connected to the second input end of the second OR gate; the output end of the second OR gate is connected to the opening increase control end of the root valve 7.

[0057] It should be noted that the utility model can flexibly control the heating amount of the electric heating tape 14 by changing the heating length and winding density of the electric heating tape 14 or using a temperature controller to cope with more complex environments.

[0058] In the description of this specification, the description with reference to the terms "preferred embodiment", "one embodiment", "some embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0059] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A liquid nitrogen gasification system for purging a large cryogenic storage tank, comprising a nitrogen delivery pipeline that can be connected to a liquid outlet of a liquid nitrogen tank truck, and a nitrogen purge pipeline for purging the cryogenic storage tank, wherein a control valve is provided at the outlet end of the nitrogen delivery pipeline, and a root valve located at the root of the purge port of the cryogenic storage tank is provided at the outlet end of the nitrogen purge pipeline; characterized in that: The nitrogen delivery pipeline is provided with an air-temperature gasifier, and the section of the nitrogen purge pipeline close to the root valve is wrapped with an electric heating belt.

2. A liquid nitrogen gasification system for purging a large cryogenic storage tank according to claim 1, characterized in that: A first pressure gauge and a first temperature gauge are provided on the nitrogen purge pipeline between the electric heating belt and the root valve.

3. A liquid nitrogen gasification system for purging a large cryogenic storage tank according to claim 2, characterized in that: A second pressure gauge and a second temperature gauge are provided on the nitrogen delivery pipeline between the air-temperature gasifier and the control valve.

4. A liquid nitrogen gasification system for purging a large cryogenic storage tank according to claim 1, characterized in that: A stop valve is provided at the inlet end of the nitrogen purge pipeline; And / or the electric heating tape is coated with a thermal insulation layer.

5. A liquid nitrogen gasification system for purging a large cryogenic storage tank according to claim 4, characterized in that: The heat-insulating layer is made of glass fiber wool.

6. A liquid nitrogen gasification system for purging a large cryogenic storage tank according to claim 1, characterized in that: The length of the nitrogen purge pipeline is not less than 50 meters.

7. A liquid nitrogen gasification system for purging a large cryogenic storage tank according to claim 2, characterized in that: Also included is a controller, the controller including a first comparator and a second comparator; The first input terminal of the first comparator is connected to the pressure analog signal output terminal of the first pressure gauge, the second input terminal of the first comparator is connected to the pressure low threshold memory, and the output terminal of the first comparator is connected to the first input terminal of the first OR gate; The first input terminal of the second comparator is connected to the temperature analog signal output terminal of the first temperature meter, the second input terminal of the second comparator is connected to the temperature low threshold memory, and the output terminal of the second comparator is connected to the second input terminal of the first OR gate; The output end of the first OR gate is connected to the opening reduction control end of the root valve.

8. A liquid nitrogen gasification system for purging a large cryogenic storage tank according to claim 7, characterized in that: The controller further includes a third comparator and a fourth comparator; The first input terminal of the third comparator is connected to the pressure analog signal output terminal of the first pressure gauge, the second input terminal of the third comparator is connected to the pressure high threshold memory, and the output terminal of the third comparator is connected to the first input terminal of the second OR gate; The first input terminal of the fourth comparator is connected to the temperature analog signal output terminal of the first temperature meter, the second input terminal of the fourth comparator is connected to the temperature high threshold memory, and the output terminal of the second comparator is connected to the second input terminal of the second OR gate; The output end of the second OR gate is connected to the opening increasing control end of the root valve.

9. A liquid nitrogen gasification system for purging a large cryogenic storage tank according to any one of claims 1 to 8, characterized in that: A vertically arranged pipe rack supported on the ground is provided on the side of the cryogenic storage tank, a public pipe gallery supported on the ground is provided on the outside of the pipe rack, the upper end of the pipe rack is connected to a tank top operating platform located on the top of the cryogenic storage tank, and the nitrogen purge pipeline is laid to the tank top operating platform through the public pipe gallery and the pipe rack.

10. A liquid nitrogen gasification system for purging a large cryogenic storage tank according to claim 9, characterized in that: The electric heating belt is wound around the outside of the nitrogen purge pipeline on the tank top operating platform.

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