Nitrogen emptying and recycling method for 400-cubic liquid nitrogen storage tank

Abstract

The invention discloses a nitrogen emptying and recycling method for a 400-cubic liquid nitrogen storage tank. The method comprises the following steps: firstly, mounting a low-temperature cyclone separator at the top of a blow-down pipe, separating liquid drops through a built-in spiral guide plate (the angle is adjustable in a range of 30-60 degrees), enabling the liquid drops to flow back to a storage tank, and leading out gaseous nitrogen through a pipeline; secondly, low-temperature nitrogen is input into a composite heat exchange reheating device and is reheated to the normal temperature by combining a heat pipe heat exchange unit (pre-cooling air by utilizing residual cold of a storage tank) and a vortex type preheating channel (with a built-in vortex generator), a pipeline is provided with a pre-cooling buffer section, and an outlet is provided with a temperature feedback regulator; and finally, shunting is performed through a self-adaptive shunting distributor, and a sensor and an adjustable valve are arranged in the self-adaptive shunting distributor and are distributed to a main tower (passing through a one-way valve) and a cold box interlayer (passing through a flow limiter) according to requirements. The recovery efficiency is improved, equipment protection is optimized, and the cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial gas recovery and utilization, and relates to a method for recycling nitrogen discharged from a 400-cubic liquid nitrogen storage tank. Background Art

[0002] As an important industrial gas, liquid nitrogen is widely used in fields such as chemical industry, metallurgy, and electronic manufacturing. Its storage usually relies on large liquid nitrogen storage tanks, such as a 400-cubic liquid nitrogen storage tank. In actual operation, due to reasons such as pressure regulation, equipment maintenance, or long-term shutdown, the excess nitrogen in the liquid nitrogen storage tank is often directly discharged into the atmosphere through the vent pipe. This venting operation not only causes serious waste of resources, but also increases the operating costs of enterprises and has a certain negative impact on the environment. Especially in large industrial systems such as the 4000 unit, the amount of vented nitrogen from the liquid nitrogen storage tank is relatively large. If not recycled and utilized, it not only violates the modern industrial concept of energy conservation and emission reduction, but also runs counter to the goal of enterprises to reduce costs and improve efficiency.

[0003] In the prior art, the treatment method for vented nitrogen from liquid nitrogen storage tanks is relatively simple and crude. The common practice is to directly discharge it into the atmosphere through the vent pipe, or in some scenarios, introduce the vented nitrogen into a vaporizer for reheating and then use it for a single purpose. For example, in some industrial systems, the vented low-temperature nitrogen is led through a pipeline to a vaporizer, and after reheating it by heat exchange with air, it is supplied to production equipment. However, this method has various limitations. First, the vented nitrogen may carry trace liquid droplets, which directly volatilize or are lost with the airflow during the discharge process without being effectively separated and reused, resulting in a low utilization rate of liquid nitrogen resources. Second, the reheating process usually relies on a single vaporizer, with low heat exchange efficiency, and does not fully utilize the low-temperature residual cold characteristics of the liquid nitrogen storage tank itself, resulting in high energy consumption. In addition, the utilization method of the reheated nitrogen is relatively single, often only used for production gas supply, and cannot simultaneously meet multiple requirements such as maintaining the pressure of the main tower, sealing the cold box and the storage tank interlayer. This limitation of single use is particularly obvious in complex industrial scenarios.

[0004] In some industrial bases, such as bridge-building bases, the heating and replacement operations of tank trucks require additional consumption of nitrogen. Due to the lack of effective nitrogen recovery means locally, tank trucks often need to be transported to other bases (such as Changshou Base) for replacement treatment, and the round-trip transportation cost is as high as 1500 yuan each time. Such long-distance transportation not only increases the operating cost but also reduces the production efficiency due to the time delay during transportation. At the same time, when the 4000-unit is shut down for a long time, key components such as the main tower, cold box, and the interlayer of the storage tank are prone to problems such as equipment corrosion and pearlite sand moisture absorption due to the lack of sealed gas for pressure maintenance. If these problems are not solved in time, it will significantly shorten the service life of the equipment, increase the maintenance cost, and even affect production safety. Traditional countermeasures usually involve purchasing external nitrogen for pressure maintenance and sealing, but this not only further increases the cost but also forms a double contradiction in resource use with the waste of vented nitrogen.

[0005] Regarding the recovery and utilization of vented nitrogen, there have also been some improvement attempts in the existing technologies. For example, some solutions propose using vaporizers with heat exchange fins to improve the reheating efficiency of low-temperature gases, but these designs are usually limited to single equipment, not deeply integrated with the venting system of the liquid nitrogen storage tank, and do not consider the separation and reuse of liquid droplets in the vented nitrogen. In addition, there are some gas distribution systems that divert nitrogen to multiple uses through pipelines and valves, such as equipment pressure maintenance or sealing, but the nitrogen sources of these solutions are mostly externally supplied, and no process optimization has been carried out for the low-temperature and high-flow characteristics of the vented nitrogen from the liquid nitrogen storage tank. In terms of diversion control, the existing technologies mostly rely on manual adjustment or static valve settings, and it is difficult to achieve dynamic distribution according to the fluctuations of the main tower pressure or the changes in the sealing gas flow rate, resulting in unsatisfactory nitrogen utilization efficiency and equipment protection effect.

[0006] In summary, the existing technologies have problems such as low resource utilization rate, insufficient reheating efficiency, and backward diversion control in the recovery and utilization of vented nitrogen from liquid nitrogen storage tanks. Especially in the specific application scenario of a 400-cubic-meter liquid nitrogen storage tank, there is a lack of targeted comprehensive solutions. These deficiencies not only limit the recycling of nitrogen resources but also cannot effectively meet the dual requirements of equipment protection and cost control. Therefore, developing a technical solution that can efficiently recover vented nitrogen, optimize the reheating process, and achieve multi-purpose dynamic distribution has become an urgent technical problem to be solved. Through innovative equipment design and process optimization, the present invention aims to overcome the above defects and provide an efficient and economical implementation approach for the recovery and utilization of industrial gases. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to solve the above problems and provide a method for recovering and utilizing the nitrogen vented from a 400-cubic-meter liquid nitrogen storage tank.

[0008] To achieve the above purpose, the present invention provides the following technical solutions:

[0009] A method for recycling nitrogen discharged from a 400-cubic-meter liquid nitrogen storage tank includes the following steps:

[0010] (1) Install an integrated cryogenic cyclone separator at the top of the discharge pipe of the 400-cubic-meter liquid nitrogen storage tank. Generate a cyclone through the built-in spiral guide plate to separate the trace liquid droplets in the discharged nitrogen and return them to the bottom of the storage tank through the return pipe. At the same time, lead out a pipeline from the outlet of the separator to transport gaseous nitrogen;

[0011] (2) Input the separated cryogenic gaseous nitrogen into a composite heat exchange and reheating device. The composite heat exchange and reheating device includes an inner-layer heat pipe heat exchange unit and an outer-layer vortex air preheating channel. Use the low-temperature residual cold of the storage tank through the heat pipe heat exchange unit to preheat the air, and then reheate the nitrogen to room temperature through the rotating air flow in the vortex channel;

[0012] (3) Shunt the reheated room-temperature nitrogen through an adaptive shunt distributor. The distributor is equipped with a pressure-flow coupling sensor inside. According to the real-time requirements of the main tower and the sealed gas pipeline network, divide the nitrogen into two paths by adjusting the opening degree of the built-in valve. One path is transported to the inside of the main tower through the valve, and the other path is transported to the sealed gas pipeline network of the cold box and the storage tank interlayer.

[0013] Further, the air flow rotation speed formed by the spiral guide plate of the cryogenic cyclone separator is adjustable. The angle range of the guide plate is 30° to 60°, and it is connected to the bottom of the storage tank through the return pipe at the bottom of the separator.

[0014] Further, the inner-layer heat pipe heat exchange unit of the composite heat exchange and reheating device adopts a vacuum heat pipe structure. The heat pipe is filled with a low-boiling-point working medium, and transfers the low-temperature residual cold to the external air through thermal contact with the outer wall of the storage tank.

[0015] Further, the outer-layer vortex air preheating channel of the composite heat exchange and reheating device is equipped with a vortex generator inside, which generates an air flow vortex through the rotating blades. The inlet of the vortex channel is connected to the air outlet of the heat pipe heat exchange unit.

[0016] Further, the adaptive shunt distributor includes a main control unit and at least two shunt channels. Each shunt channel is provided with an independent adjustable valve, and the main control unit adjusts the opening degree of each valve according to the signal of the pressure-flow coupling sensor.

[0017] Further, a check valve is set on the pipeline between the adaptive shunt distributor and the main tower to prevent the gas in the main tower from flowing back to the distributor; a flow limiter is set on the pipeline between the adaptive shunt distributor and the sealed gas pipeline network to control the nitrogen flow rate.

[0018] Further, a pre-cooling buffer section is added to the pipeline connecting the cryogenic cyclone separator and the composite heat exchange and reheating device. The outer wall of the buffer section is wrapped with a heat insulation layer, and a flow guide grid plate is arranged inside to slow down the nitrogen flow rate.

[0019] Furthermore, a temperature feedback regulator is provided at the outlet of the outer-layer eddy current type air preheating channel of the compound heat exchange and reheating device, and the nitrogen reheating temperature is controlled by adjusting the rotation speed of the eddy current generator.

[0020] The beneficial effects of the present invention are as follows:

[0021] A method for recycling and utilizing the nitrogen venting of a 400-cubic-meter liquid nitrogen storage tank provided by the present invention realizes the efficient recovery and multi-purpose utilization of the vented nitrogen through the synergistic effect of an integrated low-temperature cyclone separator, a compound heat exchange and reheating device, and an adaptive shunt distributor, bringing remarkable technical and economic benefits. The following elaborates its beneficial effects in detail from multiple aspects:

[0022] 1. Significantly improve the resource utilization efficiency

[0023] By installing an integrated low-temperature cyclone separator at the top of the vent pipe, the present invention utilizes the swirling effect generated by the spiral guide plate to efficiently separate the trace liquid droplets entrained in the vented nitrogen and return them to the bottom of the storage tank through the return pipe. Compared with traditional direct discharge or simple pipe leading, this design effectively reduces the evaporation loss of liquid nitrogen, enabling the reuse of liquid resources during the venting process. At the same time, the separated pure gaseous nitrogen enters the subsequent reheating and distribution links, avoiding the potential impact of liquid droplets on downstream equipment. This innovative design of liquid-gas separation and reflux not only maximizes the recovery rate of nitrogen resources but also provides a higher-quality gas source for the subsequent reheating process, thus significantly improving the overall resource utilization efficiency.

[0024] 2. Optimize the equipment protection effect

[0025] The present invention dynamically distributes the reheated normal-temperature nitrogen to the sealed gas pipe networks inside the main tower, in the cold box, and in the storage tank interlayer through an adaptive shunt distributor, meeting the multiple requirements of equipment pressure maintenance and sealing. In the scenario of long-term shutdown, the internal pressure of the main tower is prone to imbalance due to the lack of pressure-maintaining gas, and the cold box and the storage tank interlayer are prone to air penetration due to the lack of sealing gas protection, which may lead to problems such as equipment corrosion and pearlite sand moisture absorption. Through the pressure-flow coupling sensor built in the adaptive shunt distributor, the present invention can adjust the nitrogen distribution ratio according to the real-time requirements of the main tower and the sealed gas pipe network, ensuring the stability of the internal pressure of the main tower and maintaining a good sealing state of the cold box and the storage tank interlayer. This dynamic protection mechanism effectively reduces the risk of equipment corrosion and extends the service life of key components, providing a reliable guarantee for the efficient operation of the industrial system.

[0026] 3. Greatly reduce the operating cost

[0027] By recycling and reusing the vented nitrogen, the present invention significantly reduces the need for external nitrogen procurement. In traditional methods, the pressure maintenance of the main tower and the sealing gas often rely on nitrogen purchased additionally, and the waste of vented nitrogen further exacerbates the resource cost. The present invention utilizes the nitrogen vented from the liquid nitrogen storage tank itself, which is directly used for equipment protection after cyclone separation and reheating, without the need for additional gas source supplementation, thereby reducing the nitrogen procurement cost. In addition, in some industrial bases (such as the bridge construction base), the tank truck heating and replacement need to be transported to other locations (such as the Changshou base), and the round-trip cost is about 1500 yuan each time. The present invention meets the tank truck demand by locally recycling nitrogen, eliminating the necessity of long-distance transportation, and can save hundreds of thousands of yuan in transportation costs annually. This cost optimization conforms to the enterprise's concept of "operating by calculating", providing strong support for improving economic efficiency.

[0028] 4. Improve the energy-saving performance of the reheating process

[0029] The composite heat exchange and reheating device adopted in the present invention combines an inner-layer heat pipe heat exchange unit and an outer-layer eddy current air preheating channel, making full use of the low-temperature waste heat of the liquid nitrogen storage tank. The heat pipe heat exchange unit transfers the low-temperature waste heat to the external air through thermal contact with the outer wall of the storage tank to realize the precooling of the air; the outer-layer eddy current channel enhances the heat exchange efficiency through the rotating air flow and reheats the nitrogen from -195°C to normal temperature. Compared with the traditional vaporizer with single air heat exchange, this composite heat exchange design not only improves the heat exchange efficiency but also reduces the dependence on external heat sources, significantly reducing the energy consumption. In addition, the temperature feedback regulator at the outlet of the eddy current channel can dynamically adjust the rotation speed of the eddy current generator according to the nitrogen temperature, further optimizing the energy efficiency of the reheating process and ensuring that the nitrogen temperature is stably within an appropriate range. This energy-saving reheating process provides a green and efficient solution for industrial gas treatment.

[0030] 5. Enhance the stability and adaptability of the system

[0031] The technical design of the present invention fully considers the characteristics of the vented nitrogen from the 400-cubic-meter liquid nitrogen storage tank and the complexity of its application scenarios. For example, the angle of the spiral guide plate of the low-temperature cyclone separator can be adjusted within the range of 30° to 60°, which can adapt to the liquid-gas separation requirements under different venting flows; the precooling buffer section on the pipeline slows down the nitrogen gas flow rate through the heat insulation layer and the guide grid plate, avoiding the impact of the low-temperature gas flow on the downstream equipment; the pressure-flow coupling control of the adaptive shunt distributor realizes the intelligent and precise distribution of nitrogen. These designs together improve the operation stability of the system, enabling it to flexibly respond to dynamic conditions such as the main tower pressure fluctuation and the sealing gas flow change. In addition, the setting of the check valve and the flow limiter further prevents gas backflow and flow out of control, ensuring the reliability of the system under various operating conditions.

[0032] 6. Promote the wide application of the technology

[0033] The technical solution of the present invention is not only applicable to 400 cubic liquid nitrogen storage tanks, but can also be extended to other capacities or types of liquid gas storage tanks, such as the venting and recycling of liquid oxygen and liquid argon storage tanks. Its core components (such as cyclone separators, composite heat exchange devices, and adaptive distributors) have the potential for modular design and can be customized according to the venting flow and downstream needs of different storage tanks. This versatility and flexibility make the present invention have a strong promotion value in the field of industrial gases, and lay the foundation for creating a professional gas recovery technology with market competitiveness.

[0034] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. DETAILED DESCRIPTION

[0035] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] A method for venting and recycling nitrogen from a 400 cubic meter liquid nitrogen storage tank comprises the following steps:

[0037] (1) An integrated cryogenic cyclone separator is installed on the top of the vent pipe of the 400 cubic meter liquid nitrogen storage tank. A cyclone is generated through a built-in spiral guide plate to separate the trace droplets in the vented nitrogen and return them to the bottom of the storage tank through a reflux pipe. At the same time, a pipeline is drawn out from the separator outlet to transport gaseous nitrogen;

[0038] (2) The separated low-temperature gaseous nitrogen is input into a composite heat exchange and reheating device, which includes an inner heat pipe heat exchange unit and an outer vortex air preheating channel. The heat pipe heat exchange unit uses the low-temperature residual cooling of the storage tank to precool the air, and then the nitrogen is reheated to room temperature through the rotating airflow in the vortex channel;

[0039] (3) The reheated room temperature nitrogen is diverted through an adaptive diversion distributor, which has a built-in pressure-flow coupling sensor. According to the real-time needs of the main tower and the sealed gas pipeline network, the nitrogen is divided into two paths by adjusting the opening of the built-in valve. One path is transported to the inside of the main tower through the valve, and the other path is transported to the sealed gas pipeline network between the cold box and the storage tank interlayer.

[0040] Example 1: Transformation of Nitrogen Recovery and Utilization for a 400-cubic-meter Liquid Nitrogen Storage Tank in a Chemical Plant

[0041] In the 4000 unit of a chemical plant, a transformation of nitrogen vent recovery and utilization was carried out on a 400-cubic-meter liquid nitrogen storage tank. The specific steps are as follows:

[0042] 1. Installation and operation of the cryogenic cyclone separator: An integrated cryogenic cyclone separator was installed at the top of the vent pipe of the 400-cubic-meter liquid nitrogen storage tank. The separator is equipped with spiral guide plates inside, and the angle of the guide plates is set at 45°. The rotational speed of the air flow can be adjusted by regulating the inlet air flow rate (the range is 30° to 60°). After the vented nitrogen enters the separator, the trace liquid droplets are separated to the wall under the action of the swirl and are connected to the bottom of the storage tank through the bottom return pipe and returned to the storage tank; the gaseous nitrogen is led out from the top outlet of the separator and transported to the downstream through a DN40 stainless steel pipe.

[0043] 2. Application of the compound heat exchange and reheating device: The separated cryogenic gaseous nitrogen is input into a compound heat exchange and reheating device. This device includes an inner layer heat pipe heat exchange unit and an outer layer eddy current type air preheating channel. The heat pipe heat exchange unit adopts a vacuum heat pipe structure and is filled with a low-boiling-point working fluid (propane). The low-temperature residual cold is transferred to the external air through heat contact with the outer wall of the storage tank; an eddy current generator is installed inside the outer layer eddy current channel, and air vortices are generated by rotating blades. The inlet of the eddy current channel is connected to the air outlet of the heat pipe heat exchange unit. After the air is pre-cooled, it exchanges heat with the nitrogen to reheat the nitrogen to about 20°C. A temperature feedback regulator is set at the outlet of the eddy current channel to control the nitrogen reheating temperature by adjusting the rotational speed of the eddy current generator. A pre-cooling buffer section was added to the pipeline connecting the cryogenic cyclone separator and the compound heat exchange device. The outer wall of the buffer section is wrapped with an insulating layer, and a flow guiding grid plate is arranged inside to slow down the nitrogen flow rate.

[0044] 3. Operation of the adaptive shunt distributor: The reheated normal-temperature nitrogen enters an adaptive shunt distributor. This distributor includes a main control unit and two shunt channels, and each channel is equipped with an independent adjustable valve. The main control unit adjusts the opening degree of each valve according to the signal of the built-in pressure-flow coupling sensor. One-way nitrogen is transported to the inside of the main tower through valve V303, and a check valve is set on the pipeline to prevent the gas in the main tower from flowing back to the distributor; the other way is transported to the sealed gas pipe network of the cold box and the storage tank interlayer, and a flow limiter is set on the pipeline to control the nitrogen flow rate. The main control unit dynamically adjusts the shunt ratio according to the main tower pressure and the requirements of the sealed gas pipe network.

[0045] Operation verification shows that the system recovers about 200 cubic meters of nitrogen per day, the pressure of the main tower is stable above 0.15 MPa, and the sealing effects of the cold box and the interlayer are good.

[0046] Example 2: Application of Shutdown Protection for a 400-cubic-meter Liquid Nitrogen Storage Tank in a Metallurgical Enterprise

[0047] 1. In the 4000 unit of a metallurgical enterprise, for the nitrogen venting recovery requirement of a 400-cubic-meter liquid nitrogen storage tank during long-term shutdown, the following transformation was implemented:

[0048] 2. Installation and operation of the cryogenic cyclone separator: An integrated cryogenic cyclone separator was installed at the top of the vent pipe of the 400-cubic-meter liquid nitrogen storage tank. The separator is internally equipped with spiral guide plates, and the initial angle of the guide plates is set at 60° (adjustable range: 30° - 60°). The rotation speed of the air flow is controlled by manually adjusting the intake valve. The vented nitrogen enters the separator, and the trace liquid droplets are separated by cyclone and then communicated with the bottom of the storage tank through the bottom return pipe and returned to the storage tank; the gaseous nitrogen is led out from the separator outlet and transported to the downstream through a DN40 stainless steel pipe.

[0049] 3. Application of the composite heat exchange and reheating device: The separated low-temperature gaseous nitrogen is input into a composite heat exchange and reheating device. This device includes an inner-layer heat pipe heat exchange unit and an outer-layer vortex air preheating channel. The heat pipe heat exchange unit adopts a vacuum heat pipe structure and is filled with a low-boiling-point working fluid (ethane). The low-temperature residual cold is transferred to the external air through thermal contact with the outer wall of the storage tank; the outer-layer vortex channel is internally equipped with a vortex generator, and air vortices are generated by rotating blades. The inlet of the vortex channel is connected to the air outlet of the heat pipe heat exchange unit. The air is pre-cooled and then exchanges heat with the nitrogen to reheat the nitrogen to about 25°C. A temperature feedback regulator is set at the outlet of the vortex channel, and the reheating temperature of the nitrogen is controlled by adjusting the rotation speed of the vortex generator (range: 0 - 300 rpm). A pre-cooling buffer section is added to the pipe connecting the cryogenic cyclone separator and the composite heat exchange device. The outer wall of the buffer section is wrapped with an insulating layer, and a flow guide grid is arranged inside to slow down the nitrogen flow rate and ensure the stability of the air flow.

[0050] Operation of the adaptive flow divider: The reheated normal-temperature nitrogen enters an adaptive flow divider. This divider includes a main control unit and two flow-dividing channels. Each channel is equipped with an independent adjustable valve. The main control unit adjusts the opening degree of each valve according to the signal of the built-in pressure-flow coupling sensor. One-way nitrogen is transported to the inside of the main tower through valve V303, and a one-way valve is set on the pipe to prevent the gas in the main tower from flowing back to the divider; the other way is transported to the sealed gas pipe network of the cold box and the storage tank interlayer, and a flow limiter is set on the pipe to control the nitrogen flow rate at 50 - 80 m 3 / h. The main control unit dynamically adjusts the flow-dividing ratio according to the low-pressure demand of the main tower and the sealing requirement of the interlayer during shutdown.

[0051] Operation verification shows that the system effectively recovers about 6000 cubic meters of vented nitrogen within one month of shutdown, the pressure inside the main tower remains stable, there is no sign of air infiltration in the interlayer, and the equipment protection effect is remarkable.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for venting and recycling nitrogen from a 400 cubic meter liquid nitrogen storage tank, characterized in that: The steps include: (1) An integrated cryogenic cyclone separator is installed on the top of the vent pipe of the 400 cubic meter liquid nitrogen storage tank. A cyclone is generated through a built-in spiral guide plate to separate the trace droplets in the vented nitrogen and return them to the bottom of the storage tank through a reflux pipe. At the same time, a pipeline is drawn out from the separator outlet to transport gaseous nitrogen; (2) The separated low-temperature gaseous nitrogen is input into a composite heat exchange and reheating device, which includes an inner heat pipe heat exchange unit and an outer vortex air preheating channel. The heat pipe heat exchange unit uses the low-temperature residual cooling of the storage tank to precool the air, and then the nitrogen is reheated to room temperature through the rotating airflow in the vortex channel; (3) The reheated room temperature nitrogen is diverted through an adaptive diversion distributor, which has a built-in pressure-flow coupling sensor. According to the real-time needs of the main tower and the sealed gas pipeline network, the nitrogen is divided into two paths by adjusting the opening of the built-in valve. One path is transported to the inside of the main tower through the valve, and the other path is transported to the sealed gas pipeline network between the cold box and the storage tank interlayer.

2. The method according to claim 1, characterized in that: The airflow rotation speed formed by the spiral guide plate of the low-temperature cyclone separator is adjustable, the angle range of the guide plate is 30° to 60°, and it is connected to the bottom of the storage tank through the reflux pipe at the bottom of the separator.

3. The method according to claim 1, characterized in that: The inner heat pipe heat exchange unit of the composite heat exchange and reheating device adopts a vacuum heat pipe structure. The heat pipe is filled with a low-boiling point working fluid, and the low-temperature residual cold is transferred to the external air through thermal contact with the outer wall of the storage tank.

4. The method according to claim 1, characterized in that: The outer vortex air preheating channel of the composite heat exchange and reheating device has a built-in vortex generator, which generates an air flow vortex through rotating blades. The inlet of the vortex channel is connected to the air outlet of the heat pipe heat exchange unit.

5. The method according to claim 1, characterized in that: The adaptive flow splitter distributor comprises a main control unit and at least two flow split channels. Each flow split channel is provided with an independent adjustable valve. The main control unit adjusts the opening of each valve according to the signal of the pressure-flow coupling sensor.

6. The method according to claim 5, characterized in that: A one-way valve is arranged on the pipeline between the adaptive flow splitter and the main tower to prevent the gas in the main tower from flowing back to the distributor; a flow limiter is arranged on the pipeline between the adaptive flow splitter and the main tower to control the nitrogen flow.

7. The method according to claim 1, characterized in that: A precooling buffer section is added to the pipeline connecting the low-temperature cyclone separator and the composite heat exchange and reheating device. The outer wall of the buffer section is wrapped with an insulation layer, and a guide grid is arranged inside to slow down the nitrogen flow rate.

8. The method according to claim 1, characterized in that: A temperature feedback regulator is arranged at the outlet of the outer vortex air preheating channel of the composite heat exchange and reheating device, and the nitrogen reheating temperature is controlled by adjusting the rotation speed of the vortex generator.