Liquid nitrogen supply method without evaporation and liquid nitrogen supply without liquid nitrogen supply

Abstract

The application relates to a liquid nitrogen supply method without liquid nitrogen supplement and zero evaporation, which comprises the following steps: separating high-purity nitrogen from ambient air; cooling and storing the high-purity nitrogen in a liquid nitrogen collecting tank through a cold head of a refrigerator; when the liquid level of a gas-phase liquid nitrogen tank is lower than a set lower limit value, automatically opening a liquid supplement electromagnetic valve, distributing liquid nitrogen to the gas-phase liquid nitrogen tank through a gas-liquid separator, and realizing liquid nitrogen supplement by gravity flow; recycling the nitrogen gas volatilized in the gas-phase liquid nitrogen tank through a collection return pipeline, temporarily storing and buffering the nitrogen gas in a gas buffer tank, and then conveying the nitrogen gas to the cold head of the refrigerator for re-liquefaction; when the total liquid nitrogen loss of the system occurs, increasing the output of nitrogen gas preparation, supplementing the liquefied nitrogen to the liquid nitrogen collecting tank, and the like. Through on-site nitrogen preparation, nitrogen gas closed-loop recycling and re-liquefaction, and multi-source dynamic compensation, the application realizes independent continuous operation without external liquid nitrogen supplement and zero evaporation, completely gets rid of the dependence on external liquid nitrogen distribution, and greatly improves the sample storage safety and the system operation economy.

Description

Technical Field

[0001] This invention relates to the field of liquid nitrogen storage and supply technology, and in particular to a zero-evaporation liquid nitrogen supply method that eliminates the need for liquid nitrogen replenishment. Background Technology

[0002] Biobanks are core facilities for preserving precious biological resources such as stem cells, embryos, and tissue samples. Liquid nitrogen, as the cryogenic medium for deep cryogenic storage, has a stable supply that directly affects the long-term safety of the samples. Currently, biobanks primarily rely on external supply chains for liquid nitrogen, which generally presents the following technical challenges: (1) High risk of supply interruption: The mode of liquid nitrogen being delivered by gas companies to liquid nitrogen towers or manually transported and filled has a significant risk of delay. Failure to maintain liquid nitrogen towers and vacuum pipelines can easily lead to supply interruption.

[0003] (2) The safety of samples is a major threat: Most existing liquid nitrogen supply systems are built-in designs, with the refrigeration or liquefaction components installed inside the liquid nitrogen tank. Once a malfunction occurs, the liquid nitrogen tank needs to be disassembled for repair, which is not only complicated to operate, but also seriously interferes with the storage environment of the samples inside the tank. At the same time, the built-in structure occupies the effective storage space inside the tank, reducing the storage density.

[0004] (3) Serious waste of nitrogen volatilization: The nitrogen generated by the natural volatilization of liquid nitrogen in the gas phase liquid nitrogen tank is directly discharged into the environment, resulting in waste of cooling capacity and high operating costs; the existing system lacks an effective mechanism for recycling and reusing volatilized nitrogen.

[0005] (4) Low level of automation: Existing liquid nitrogen replenishment mostly relies on manual or semi-automatic methods. Liquid level monitoring, replenishment control, fault alarm and other links require manual intervention, resulting in high operation and maintenance costs and difficulty in achieving coordinated liquid supply from multiple devices.

[0006] (5) Insufficient batch liquid supply capacity: Most existing liquid nitrogen generators are single-unit integrated designs, which cannot meet the batch liquid supply needs of multiple liquid nitrogen tanks at the same time, resulting in poor scalability.

[0007] To address the aforementioned technical issues, some improvements have been made in existing technologies. For example, there are liquid nitrogen generators on the market based on GM refrigerators that integrate PSA nitrogen generation, refrigeration liquefaction, and storage functions, enabling on-site nitrogen generation and liquid nitrogen preparation. However, existing solutions either embed the refrigeration system, interfering with the sample storage environment, or fail to achieve coordinated liquid supply from multiple devices and efficient closed-loop operation. Neither solution fundamentally addresses the problems of external source dependence, maintenance difficulties, and insufficient batch liquid supply capacity.

[0008] Therefore, there is an urgent need for a technical solution that can simultaneously address dependence on external liquid nitrogen, nitrogen volatilization and waste, difficulties in bulk liquid supply, and system maintenance risks. Summary of the Invention

[0009] The purpose of this invention is to overcome the technical defects of existing liquid nitrogen supply methods, such as reliance on external delivery, nitrogen evaporation and waste, maintenance interference with sample storage environment, and insufficient batch liquid supply capacity. It provides a zero-evaporation liquid nitrogen supply method that eliminates the need for liquid nitrogen replenishment, realizing integrated autonomous continuous operation of on-site nitrogen generation, on-site liquefaction, nitrogen recovery, and closed-loop liquid replenishment.

[0010] The objective of this invention is achieved as follows: A zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment is based on an external zero-evaporation liquid nitrogen system without liquid nitrogen replenishment. The system includes a nitrogen generator, a refrigerator cold head, a liquid nitrogen collection tank, a gas-liquid separator, a gas buffer tank, and at least one gas phase liquid nitrogen tank. The nitrogen generator is connected to the cold head of the refrigerator via a pipeline; the cold head of the refrigerator is connected to the liquid nitrogen collection tank via a flange; the liquid nitrogen collection tank is first connected to a common pipeline, which is connected to a gas-liquid separator and a gas buffer tank via two branch pipes; the gas-liquid separator is connected to each gas phase liquid nitrogen tank via a pipeline; each gas phase liquid nitrogen tank is connected to the main pipeline via a gas collection return pipeline, which is connected to the cold head of the refrigerator. The branch pipe connected to the gas-liquid separator is connected to a liquid nitrogen supply port and a liquid nitrogen output port via pipelines; the cold head of the refrigerator is also connected to a nitrogen output port. The above-mentioned zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment includes the following: S1. Nitrogen preparation: High-purity nitrogen is separated from ambient air using membrane separation technology or PSA pressure swing adsorption technology; S2, Nitrogen liquefaction: High-purity nitrogen is liquefied by cooling the cold head of a refrigeration unit and stored in a liquid nitrogen collection tank; S3, Liquid nitrogen distribution and supply: When the liquid level in the gas phase liquid nitrogen tank is lower than the set lower limit, the liquid replenishment solenoid valve is automatically opened, and liquid nitrogen is distributed to the gas phase liquid nitrogen tank through the gas-liquid separator, and liquid nitrogen replenishment is achieved by gravity flow. S4. Nitrogen recovery and reliquefaction: Nitrogen volatilized in the gas phase liquid nitrogen tank is recovered through the gas collection and return pipeline, temporarily stored and buffered in the gas buffer tank, and then transported to the cold head of the refrigerator for reliquefaction. S5. System Loss Compensation: When the total liquid nitrogen in the system is lost, the output of nitrogen production is increased, and after liquefaction, it is replenished to the liquid nitrogen collection tank to maintain the dynamic balance of the total liquid nitrogen in the system.

[0011] Furthermore, in step S3, the gas-liquid separator integrates temperature, pressure, and level transmitters as well as an automatic control solenoid valve to ensure stable and smooth transport of low-temperature media in the pipeline.

[0012] Furthermore, in step S4, the recovered nitrogen is temporarily stored in a gas buffer tank to buffer pressure fluctuations and ensure the stable and continuous reliquefaction process.

[0013] Furthermore, in step S2, the cold head of the refrigeration unit adopts a GM refrigeration unit or a pulse tube refrigeration unit, with a liquid nitrogen output of 4-5 L / h, and liquid nitrogen is produced 10-20 seconds after the gas is introduced.

[0014] Furthermore, in step S1, the purity of the high-purity nitrogen gas is ≥99.5%, and the output pressure is 0.7-1.0 MPa.

[0015] Furthermore, in step S3, a common pipeline is provided between the liquid nitrogen collection tank and the gas-liquid separator, and a solenoid valve, a pressure sensor and a safety valve are sequentially installed on the common pipeline.

[0016] Furthermore, in step S3, a liquid replenishment solenoid valve is installed on the connecting pipeline between the gas-liquid separator and each gas phase liquid nitrogen tank, and each gas phase liquid nitrogen tank is equipped with an outlet solenoid valve, a pressure sensor and a level gauge. A one-way valve is installed on the gas collection return pipeline of each gas phase liquid nitrogen tank.

[0017] Furthermore, the pipeline used to transport liquid nitrogen or cryogenic nitrogen is a vacuum pipeline. The vacuum pipeline includes an inner tube and an outer tube that are coaxial and nested together. The inner tube and the outer tube are connected by a high-vacuum multilayer insulation structure. There are several support members arranged along the axial direction between the outer tube and the inner tube. A vacuum extraction port is provided on the outer tube.

[0018] Furthermore, it also includes an emergency liquid replenishment procedure: in the event of a system failure, direct liquid nitrogen replenishment can be carried out through the reserved liquid nitrogen replenishment interface.

[0019] Furthermore, it also includes off-peak electricity operation procedures: liquid nitrogen is prepared and stored centrally during off-peak electricity hours and shut down during peak hours.

[0020] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a zero-evaporation liquid nitrogen supply method that eliminates the need for liquid nitrogen replenishment, which has the following specific advantages: (1) Completely get rid of dependence on external liquid nitrogen: Through the integrated process of on-site air nitrogen generation and in-situ liquefaction, the independent and continuous supply of liquid nitrogen is realized, eliminating the sample safety risk caused by delivery delays or interruptions, and fundamentally ensuring the continuity of sample storage; the liquid nitrogen supply method of the present invention can produce 80-100L of liquid nitrogen per day, which can meet the replenishment needs of 14-16 standard gas phase liquid nitrogen tanks.

[0021] (2) Zero evaporation closed-loop operation: Through the nitrogen recovery and reliquefaction process, all the nitrogen volatilized in the gas phase liquid nitrogen tank is recovered and reused, realizing zero evaporation operation of liquid nitrogen and greatly reducing operating costs; the nitrogen recovery path and the fresh nitrogen preparation path run in parallel, and the system can automatically switch the gas supply source according to the liquid level and pressure parameters.

[0022] (3) External multi-unit layout: The cooling core component is independently arranged outside the gas phase liquid nitrogen tank. System maintenance and repair operations do not require entering the sample storage area, do not interfere with the sample storage environment inside the tank, and greatly improve the safety of biological samples. One cooling core component can supply liquid to multiple gas phase liquid nitrogen tanks at the same time, with strong scalability.

[0023] (4) Full-process automated control: The PLC control system collects temperature, liquid level, pressure and operating status parameters in real time, and automatically controls the start and stop of the solenoid valve, the cold head of the refrigeration unit and the nitrogen generator, so as to realize the unattended operation of the entire process of pressure, liquid level, nitrogen generation, liquefaction and liquid replenishment; The liquid nitrogen system used in the liquid nitrogen supply method of the present invention has data storage, historical curves, human-machine interaction, equipment status monitoring, maintenance prompts and remote upload functions to the cloud platform.

[0024] (5) Multi-scenario adaptability: It has reserved an external liquid nitrogen supply interface and a multi-channel liquid nitrogen output interface, which can supply liquid to equipment such as programmable cooling instruments and aluminum cryogenic containers at the same time. The nitrogen output interface can supply gas to nitrogen manifolds, nitrogen replacement devices, etc., and has strong multi-scenario adaptability.

[0025] (6) Energy-saving and low-carbon operation: Liquid nitrogen can be prepared and stored in a centralized manner during off-peak hours and shut down during peak hours, further reducing operating costs and carbon emissions.

[0026] (7) High reliability redundancy design: The system has sufficient cooling capacity and can be expanded to accommodate multiple biological sample tanks; at the same time, an external liquid nitrogen supply interface is reserved as a backup cold source to achieve multi-level safety redundancy protection. Attached Figure Description

[0027] Figure 1 This is a system structure diagram of an external, liquid nitrogen-free, zero-evaporation liquid nitrogen system according to Embodiment 1 of the present invention.

[0028] Figure 2 This is a cross-sectional schematic diagram of the vacuum pipeline in Embodiment 1 of the present invention.

[0029] Figure 3 This is a system structure diagram of an external, liquid nitrogen-free, zero-evaporation liquid nitrogen system according to Embodiment 2 of the present invention.

[0030] in: 1. Nitrogen generator, 2. Liquid nitrogen collection tank, 3. Refrigeration unit cold head, 4. Gas-liquid separator, 5. Gas buffer tank, 6. First gas phase liquid nitrogen tank, 7. Second gas phase liquid nitrogen tank, 8. Third gas phase liquid nitrogen tank, 9. Vacuum pipeline, 9.1 Inner pipe, 9.2 Outer pipe, 9.3 Support component, 9.4 Vacuum extraction port, 10. Liquid nitrogen supply interface, 11. Liquid nitrogen output interface, 12. Nitrogen output interface. Detailed Implementation

[0031] To better understand the technical solution of the present invention, a detailed description will be provided below in conjunction with relevant illustrations. It should be understood that the specific embodiments described below are not intended to limit the specific implementation of the technical solution of the present invention, but are merely possible implementations of the technical solution of the present invention. It should be noted that the descriptions of the positional relationships of the components herein, such as component A being located above component B, are based on the relative positions of the components in the illustrations and are not intended to limit the actual positional relationships of the components.

[0032] See Figures 1-3 As shown in the figure, the present invention relates to a zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment, which is based on an external zero-evaporation liquid nitrogen system without liquid nitrogen replenishment. The system includes a nitrogen generator, a chiller cold head, a liquid nitrogen collection tank, a gas-liquid separator, a gas buffer tank, and at least one gas phase liquid nitrogen tank.

[0033] The nitrogen generator is connected to the cold head of the refrigerator via pipeline to supply high-purity nitrogen to the cold head. The cold head is connected to a liquid nitrogen collection tank via pipeline to liquefy nitrogen into liquid nitrogen and store it in the liquid nitrogen collection tank. The liquid nitrogen collection tank is connected to a gas-liquid separator and a gas buffer tank via pipeline. The gas-liquid separator is connected to each gas phase liquid nitrogen tank via pipeline to supply liquid nitrogen to each gas phase liquid nitrogen tank. Each gas phase liquid nitrogen tank is connected to a main pipeline via a gas collection return pipeline, which is connected to the cold head of the refrigerator to recover the nitrogen volatilized in the gas phase liquid nitrogen tank and return it to the cold head of the refrigerator for reliquefaction.

[0034] The liquid nitrogen collection tank is first connected to a common pipeline, which is connected to a gas-liquid separator and a gas buffer tank via two branch pipes. The branch pipe connected to the gas-liquid separator is connected to a liquid nitrogen supply port and a liquid nitrogen output port via pipelines. A branch pipe connecting the gas phase liquid nitrogen tank and the cold head of the refrigerator is provided on the main pipeline.

[0035] Each gas phase liquid nitrogen tank is equipped with an outlet solenoid valve, pressure sensor, and level gauge.

[0036] The refrigeration unit's cold head is also connected to a nitrogen output interface.

[0037] All pipelines in the system used to transport liquid nitrogen or cryogenic nitrogen are vacuum pipelines.

[0038] The nitrogen generator is a PSA pressure swing adsorption nitrogen generator, which can output high-purity nitrogen.

[0039] The system adopts a skid-mounted integrated structure, with the nitrogen generator, refrigerator cold head, liquid nitrogen collection tank, gas-liquid separator and gas buffer tank integrated on the same skid base. The gas phase liquid nitrogen tank is independently arranged outside the skid base and connected to the skid body through a vacuum pipeline.

[0040] The number of gas phase liquid nitrogen tanks is two, three or more, forming a multi-tank layout, that is, one refrigeration unit cold head simultaneously provides liquid nitrogen supply to multiple gas phase liquid nitrogen tanks.

[0041] The present invention provides a zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment, comprising the following steps: Step 1: Nitrogen preparation; The nitrogen generator is started, and high-purity nitrogen is separated from the ambient air using membrane separation technology or PSA pressure swing adsorption technology. The high-purity nitrogen is then delivered to the cold head of the refrigerator through pipelines.

[0042] Step 2: Nitrogen liquefaction and storage; The refrigeration unit's cold head is started to cool and liquefy the high-purity nitrogen gas; the liquefied liquid nitrogen is then transported through pipelines to a liquid nitrogen collection tank for storage.

[0043] Step 3: Liquid nitrogen distribution and supply; When the liquid level sensor of the gas phase liquid nitrogen tank detects that the liquid level is lower than the set lower limit, the system automatically opens the liquid replenishment solenoid valve. The liquid nitrogen in the liquid nitrogen collection tank is distributed to the corresponding gas phase liquid nitrogen tank through the gas-liquid separator, and the liquid nitrogen is replenished by gravity flow. When the liquid level reaches the set upper limit, the liquid replenishment solenoid valve automatically closes.

[0044] Step 4: Nitrogen recovery and reliquefaction; Nitrogen gas generated from the natural evaporation of liquid nitrogen in the gas phase liquid nitrogen tank is recovered through a gas collection and return pipeline, temporarily stored and buffered in a gas buffer tank, and then transported to the cold head of the refrigerator for reliquefaction. The reliquefied liquid nitrogen is then supplied back to the gas phase liquid nitrogen tank, achieving a closed-loop recycling of nitrogen gas.

[0045] Step 5: System Loss Compensation; When the system loses total liquid nitrogen due to seal leakage or sample access operations, the nitrogen generator produces supplementary nitrogen from the air, which is then liquefied by the cold head of the refrigerator and returned to the liquid nitrogen collection tank to maintain the dynamic balance of the total liquid nitrogen in the system.

[0046] Step Six: Multi-output Expansion; Liquid nitrogen is supplied to equipment such as programmed cooling instruments and aluminum cryogenic containers through the liquid nitrogen output interface; nitrogen is supplied or vented to nitrogen manifolds and nitrogen replacement devices through the nitrogen output interface.

[0047] In step three, the gas-liquid separator integrates temperature, pressure, and level transmitters as well as an automatic control solenoid valve to ensure stable and smooth transport of low-temperature media in the pipeline.

[0048] In step four, the recovered nitrogen is temporarily stored in a gas buffer tank to buffer pressure fluctuations and ensure the stability and continuity of the reliquefaction process.

[0049] In steps three and four, all pipelines used to transport liquid nitrogen or cryogenic nitrogen are vacuum high-insulation pipelines. The inner and outer pipes are connected by a high-vacuum multi-layer insulation structure, and the support components adopt a point contact / line contact design to minimize heat conduction.

[0050] The method also includes an external liquid nitrogen replenishment step: when the system malfunctions or requires emergency replenishment, direct liquid nitrogen replenishment is performed through the reserved liquid nitrogen replenishment interface to ensure the safety and reliability of the samples in the gas phase liquid nitrogen tank.

[0051] The method allows for the centralized preparation and storage of liquid nitrogen during off-peak hours and shutdown during peak hours, achieving energy-saving and low-carbon operation. Example 1

[0052] See Figures 1-2 , Figure 1 A system structure diagram of an external, liquid nitrogen-free, zero-evaporation liquid nitrogen system of Embodiment 1 has been drawn. As shown in the figure, this embodiment 1 presents a zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment, implemented based on a one-to-two external zero-evaporation liquid nitrogen system without liquid nitrogen replenishment, used for liquid nitrogen supply in a biobank. The external zero-evaporation liquid nitrogen system without liquid nitrogen replenishment includes a nitrogen generator 1, a liquid nitrogen collection tank 2, a refrigerator cold head 3, a gas-liquid separator 4, a first gas phase liquid nitrogen tank 6, and a second gas phase liquid nitrogen tank 7. The nitrogen generator 1 is connected to the refrigerator cold head 3 via a pipeline. The refrigerator cold head 3 is connected to the liquid nitrogen collection tank 2 via a flange. The liquid nitrogen collection tank 2 is connected to the gas-liquid separator 4 and a gas buffer tank 5 via pipelines. The gas-liquid separator 4 is connected to the first gas phase liquid nitrogen tank 6 and the second gas phase liquid nitrogen tank 7 via pipelines. The first gas phase liquid nitrogen tank 6 and the second gas phase liquid nitrogen tank 7 are respectively connected to a main pipeline via a gas collection return pipeline, which is connected to the refrigerator cold head 3.

[0053] The nitrogen generator 1 is connected to the refrigeration unit cold head 3 via a solenoid valve and a check valve. A pressure sensor, a temperature sensor, and a level gauge are installed on the pipeline between the refrigeration unit cold head 3 and the liquid nitrogen collection tank 2. The liquid nitrogen collection tank 2 is equipped with a manual valve and a safety valve. The liquid nitrogen collection tank 2 is first connected to a common pipeline, and then the common pipeline is connected to the gas-liquid separator 4 and the gas buffer tank 5 through two branch pipes. The common pipeline is equipped with a solenoid valve, a pressure sensor and a safety valve in sequence. The branch pipe connected to the gas-liquid separator 4 is connected to the liquid nitrogen supply interface 10 and the liquid nitrogen output interface 11 through pipelines. The branch pipe connected to the gas buffer tank 5 is equipped with a one-way valve. The liquid nitrogen supply interface 10 can perform direct liquid nitrogen supply operations, comprehensively ensuring the safety and reliability of samples in the gas phase liquid nitrogen tank; the liquid nitrogen output interface 11 can supply liquid nitrogen to equipment such as programmed cooling instruments and aluminum containers through this interface.

[0054] The main pipeline between the first gaseous liquid nitrogen tank 6 and the second gaseous liquid nitrogen tank 7 and the cold head of the refrigerator is provided with a branch line connecting to the gas buffer tank 5. The connection point between the branch line and the main pipeline and the main pipeline between the cold head of the refrigerator is provided with a pressure sensor and a solenoid valve.

[0055] The gas-liquid separator 4 is equipped with a liquid replenishment solenoid valve on the connecting pipelines to the first gas phase liquid nitrogen tank 6 and the second gas phase liquid nitrogen tank 7. The first gas phase liquid nitrogen tank 6 integrates an outlet solenoid valve, a pressure sensor and a liquid level gauge, and the second gas phase liquid nitrogen tank 7 integrates an outlet solenoid valve, a pressure sensor and a liquid level gauge. A one-way valve is provided on the gas collection and return pipeline of the first gas phase liquid nitrogen tank 6 and the second gas phase liquid nitrogen tank 7.

[0056] The refrigeration unit cold head 3 is also connected to a nitrogen output interface 12. A solenoid valve and a manual valve are provided on the connecting pipeline between the refrigeration unit cold head 3 and the nitrogen output interface 12. In practical applications, the nitrogen output interface 12 can be connected to or vented from a nitrogen manifold, a dedicated gas pipeline, or a nitrogen replacement device.

[0057] In the liquid nitrogen system of this embodiment 1, all the pipelines used are vacuum pipelines 9. The vacuum pipeline 9 includes an inner tube 9.1 and an outer tube 9.2 that are coaxial and nested together. There is a vacuum interlayer between the inner tube 9.1 and the outer tube 9.2. Several layers of heat insulation are wrapped around the outer surface of the inner tube. The heat insulation layers are made of heat insulation material. Between the outer tube 9.2 and the inner tube 9.1, there are several support members 9.3 arranged along the axial direction, which can provide point contact support with the outer tube and line contact support with the inner tube. The inner tube has several limiting pieces that can axially limit the support members 9.3. The inner tube 9.1, the outer tube 9.2, and the limiting pieces are all clearance-fitted with the support members 9.3. A vacuum extraction port 9.4 is provided on the outer tube 9.2; The inner wall of the outer tube 9.2 is also provided with an adsorbent layer.

[0058] This embodiment 1 provides a zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment, comprising the following steps: S1, Nitrogen preparation; Start nitrogen generator 1; nitrogen generator 1 adopts membrane separation technology or PSA pressure swing adsorption technology. If PSA pressure swing adsorption technology is adopted, it utilizes the difference in the adsorption capacity of zeolite molecular sieve for nitrogen and oxygen, adsorbs oxygen under pressure and desorbs nitrogen under pressure; through the alternating operation of the two towers, one tower adsorbs nitrogen while the other tower desorbs and regenerates, a continuous and uninterrupted nitrogen supply is achieved.

[0059] Nitrogen generator 1 outputs high-purity nitrogen with a purity of ≥99.5%, and the flow rate is automatically adjusted according to the needs of the cold head 3 of the refrigerator. The output pressure is 0.7-1.0MPa. The high-purity nitrogen is delivered to the cold head 3 of the refrigerator through pipelines. The solenoid valve on the pipelines opens automatically, and the check valve prevents gas backflow.

[0060] Step 2: Nitrogen liquefaction and storage; Start the refrigeration unit cold head 3; the refrigeration unit cold head 3 uses a GM refrigeration unit or a pulse tube refrigeration unit. After high-purity nitrogen enters the cold end of the refrigeration unit cold head 3, it is cooled to below -196℃, changing from a gaseous phase to a liquid phase; the liquefaction process can be started within 10-20 seconds, with a liquid nitrogen production rate of 4-5L / h. The liquefied liquid nitrogen is transported to the liquid nitrogen collection tank 2 for storage through pipelines. Pressure sensors, temperature sensors, and level gauges on the pipelines monitor the liquefaction parameters in real time; the liquid nitrogen collection tank 2 has a capacity of 300L, adopts a vacuum insulation structure, and has a daily evaporation rate of <0.5%.

[0061] Step 3: Liquid nitrogen distribution and supply; Liquid nitrogen in liquid nitrogen collection tank 2 is transported to gas-liquid separator 4 through a common pipeline; the solenoid valve, pressure sensor and safety valve on the common pipeline work together to ensure safe and stable liquid nitrogen transport.

[0062] The PLC control system receives real-time level gauge signals from each gas-phase liquid nitrogen tank. When the level sensor in the first gas-phase liquid nitrogen tank 6 detects that the liquid level is below a set lower limit (e.g., the liquid level is below 20%), the system automatically opens the replenishment solenoid valve between the gas-liquid separator 4 and the first gas-phase liquid nitrogen tank 6. Liquid nitrogen flows by gravity and is distributed to the first gas-phase liquid nitrogen tank 6 via the gas-liquid separator 4. When the liquid level reaches the set upper limit, the replenishment solenoid valve automatically closes. The liquid nitrogen replenishment process for the second gas-phase liquid nitrogen tank 7 is similar.

[0063] The gas-liquid separator 4 integrates temperature, pressure, and liquid level transmitters and an automatic control solenoid valve. During the liquid replenishment process, it separates the gas and liquid phases to prevent gaseous nitrogen from entering the liquid phase pipeline and ensure a stable and smooth liquid replenishment process. During the liquid replenishment process, the pressure of the liquid nitrogen collection tank 2 is monitored in real time through the safety valve and pressure sensor of the common pipeline to maintain a stable output.

[0064] Step 4: Nitrogen recovery and reliquefaction; Nitrogen gas generated by the natural evaporation of liquid nitrogen in the first gas phase liquid nitrogen tank 6 accumulates in the upper part of the tank. When the pressure inside the tank is higher than the upper limit of the design pressure, the system automatically opens the outlet solenoid valve of the first gas phase liquid nitrogen tank 6, and the nitrogen gas enters the main pipeline through the gas collection return pipeline and the one-way valve; the nitrogen recovery process of the second gas phase liquid nitrogen tank 7 is the same.

[0065] The recovered nitrogen is transported to the gas buffer tank 5 via the main pipeline for temporary storage. The gas buffer tank 5 serves to buffer pressure fluctuations, ensuring that the recovered nitrogen flow rate entering the cold head 3 of the refrigeration unit is stable and the pressure is constant. The main pipeline is equipped with a pressure sensor and a solenoid valve. When the system detects that the recovered nitrogen flow rate is insufficient, the solenoid valve automatically switches to replenish the fresh nitrogen prepared by the nitrogen generator 1.

[0066] The recovered nitrogen output from the gas buffer tank 5 and the supplementary nitrogen output from the nitrogen generator 1 are combined and then enter the cold head 3 of the refrigerator for reliquefaction. The reliquefied liquid nitrogen is then redistributed to each gas phase liquid nitrogen tank by the gas-liquid separator 4, forming a complete closed-loop nitrogen circulation.

[0067] Step 5: System Loss Compensation; During system operation, leakage of seals or sample storage and retrieval operations will cause a gradual loss of total liquid nitrogen. When the liquid level sensor of liquid nitrogen collection tank 2 detects a continuous drop in liquid level and the amount of nitrogen recovered from the gas phase liquid nitrogen tank is insufficient to compensate for the loss, the PLC control system automatically increases the nitrogen output of nitrogen generator 1 to produce supplementary nitrogen from the air. After being liquefied by the cold head 3 of the refrigerator, the nitrogen is added to liquid nitrogen collection tank 2 to maintain the dynamic balance of the total amount of liquid nitrogen in the system.

[0068] Step 6: Multi-output expansion; Liquid nitrogen is supplied to equipment such as programmed cooling instruments and aluminum cryogenic containers through the liquid nitrogen output interface 11; the pipeline of the liquid nitrogen output interface 11 is equipped with a manual valve and a solenoid valve, and the user can control the liquid nitrogen output as needed.

[0069] The nitrogen output interface 12 supplies or empties nitrogen to the nitrogen manifold and nitrogen replacement device. The pipeline of the nitrogen output interface 12 is equipped with a solenoid valve and a manual valve. When the pressure in the gas phase liquid nitrogen tank is too high, excess nitrogen can be released through this interface. It can also be used to supply nitrogen to other equipment in the laboratory.

[0070] Off-peak electricity operation optimization: This embodiment also allows for centralized preparation and storage of liquid nitrogen during off-peak electricity hours (e.g., from 10:00 PM to 6:00 AM the following day). During off-peak hours, the system operates at maximum capacity, filling the liquid nitrogen collection tank 2 and any additional storage containers that may be configured with liquid nitrogen. During peak hours (e.g., from 8:00 AM to 8:00 PM), the chiller head 3 and nitrogen generator 1 are shut down, and the liquid nitrogen is supplied solely to the gas phase liquid nitrogen tank from the liquid nitrogen collection tank 2. This off-peak operation mode significantly reduces electricity costs while also reducing equipment operating time and extending equipment lifespan. Example 2

[0071] See Figure 3 , Figure 3A system structure diagram of an external, zero-evaporation liquid nitrogen system without liquid nitrogen replenishment in Embodiment 2 is shown. As shown in the figure, the difference between Embodiment 2 and Embodiment 1 is that the number of gaseous liquid nitrogen tanks is three, and the system adopts a one-to-three layout.

[0072] This embodiment 2 presents a zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment. The method flow is the same as in embodiment 1, except that the gas-liquid separator 4 simultaneously distributes liquid nitrogen to three gas-phase liquid nitrogen tanks. The PLC control system independently monitors the liquid level status of each tank and controls the replenishment solenoid valves of each branch. The nitrogen recovery pipelines of the three gas-phase liquid nitrogen tanks are converged to the same main pipeline. The recovered nitrogen is buffered by the gas buffer tank 5 and then transported to the cold head 3 of the refrigeration unit for reliquefaction.

[0073] The system has a daily output of 80-100L, and can meet the full replenishment of the three gas phase liquid nitrogen tanks by running for about 6 hours a day. During other times, the system can be shut down to save energy or expand the liquid supply. Example 3

[0074] The difference between Example 3 and Example 1 is the addition of an emergency manual liquid replenishment backup plan. When the system malfunctions, such as a nitrogen generator failure, a chiller cold head failure, or a control system failure, resulting in the inability to automatically replenish liquid, the operator can directly replenish liquid nitrogen through the reserved liquid nitrogen supply interface 10.

[0075] The specific operating steps are as follows: S1. Close the solenoid valve on the common pipeline between liquid nitrogen collection tank 2 and gas-liquid separator 4 to cut off the automatic liquid replenishment path; S2. Connect the delivery pipeline of the external liquid nitrogen supply tank to the liquid nitrogen supply interface 10; S3. Open the valve at the liquid nitrogen supply interface 10, manually control the liquid supply volume, and directly deliver the liquid nitrogen to the gas-liquid separator 4, and then distribute it to each gas phase liquid nitrogen tank; S4. After replenishing the liquid, close the valve and disconnect the connection. Once the system fault has been resolved, resume automatic operation.

[0076] The emergency manual liquid replenishment scheme in Example 3 provides reliable safety redundancy for the system, comprehensively ensuring the safety of the samples inside the gas phase liquid nitrogen tank.

[0077] Working principle: This invention relates to a zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment, based on the synergistic effect of the following core mechanisms: (1) On-site nitrogen generation and liquefaction integrated mechanism: High-purity nitrogen is separated from ambient air on-site using membrane separation technology or PSA pressure swing adsorption technology, and then liquefied into liquid nitrogen through the cold head of the refrigerator. The PSA dual towers work alternately to achieve continuous nitrogen supply. There are no moving parts at the low temperature end of the refrigerator cold head. Liquid nitrogen can be produced within 10-20 seconds after the gas is turned on, achieving rapid start-up and high-efficiency conversion. This mechanism eliminates the dependence on external liquid nitrogen delivery from the source.

[0078] (2) Closed-loop nitrogen recovery and reliquefaction mechanism: The nitrogen generated by the volatilization of liquid nitrogen in the gas phase liquid nitrogen tank due to natural heat conduction is recovered, temporarily stored and buffered in a gas buffer tank, and then transported to the cold head of the refrigerator for reliquefaction. The reliquefied liquid nitrogen is then replenished to the gas phase liquid nitrogen tank, forming a complete closed-loop cycle of "vaporization-recovery-liquefaction-replenishment". The introduction of the gas buffer tank solves the problem of unstable nitrogen flow rate during recovery, ensuring the continuity and stability of the reliquefaction process.

[0079] (3) Gravity-driven liquid replenishment mechanism: The liquefied liquid nitrogen is replenished to the gas phase liquid nitrogen tank by gravity, without the need for an additional power device. The gas-liquid separator separates the gas and liquid phases during the replenishment process to prevent gas phase nitrogen from entering the liquid phase pipeline and affecting the replenishment effect. The replenishment solenoid valve is automatically controlled to open and close based on the feedback signal from the liquid level sensor, so as to achieve precise liquid level management.

[0080] (4) Dynamic compensation and multi-source switching mechanism: The system has two gas supply paths: fresh nitrogen preparation and recycled nitrogen reliquefaction. When the amount of recycled nitrogen is insufficient, the system automatically switches to the fresh nitrogen preparation path to supplement it; when the total liquid nitrogen of the system is lost, it is compensated by increasing the nitrogen production output. The automatic switching and dynamic compensation of the two paths ensure the continuous and stable operation of the system.

[0081] (5) Multi-level safety redundancy mechanism: The system is equipped with multi-level safety protection such as low liquid level alarm, high pressure alarm, and abnormal temperature alarm, and reserves an external liquid nitrogen supply interface as an emergency backup cold source. While the system operates automatically, a manual intervention channel is retained to achieve a safe operation mode of "automation as the main method and manual intervention as the auxiliary method".

[0082] (6) Intelligent energy-saving operation mechanism: The PLC control system automatically adjusts the operation strategy according to the peak and valley electricity price periods of the power grid. During the valley electricity period, liquid nitrogen is prepared and stored in a concentrated manner, and the system is shut down during the peak period. The liquid nitrogen collection tank is used to maintain the liquid supply, thereby achieving optimized management of energy consumption costs.

[0083] The above are merely specific application examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. All technical solutions formed by equivalent transformations or substitutions fall within the scope of protection of the present invention.

Claims

1. A zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment, characterized in that: Based on an external, zero-evaporation liquid nitrogen system that does not require liquid nitrogen replenishment, the system includes a nitrogen generator (1), a chiller cold head (3), a liquid nitrogen collection tank (2), a gas-liquid separator (4), a gas buffer tank (5), and at least one gas phase liquid nitrogen tank. The nitrogen generator (1) is connected to the refrigeration unit cold head (3) via a pipeline; the refrigeration unit cold head (3) is connected to the liquid nitrogen collection tank (2) via a flange; the liquid nitrogen collection tank (2) is first connected to a common pipeline, which is connected to the gas-liquid separator (4) and the gas buffer tank (5) via two branch pipes; the gas-liquid separator (4) is connected to each gas phase liquid nitrogen tank via a pipeline; each gas phase liquid nitrogen tank is connected to the main pipeline via a gas collection return pipeline, which is connected to the refrigeration unit cold head (3). The branch pipe connected to the gas-liquid separator (4) is connected to a liquid nitrogen supply port (10) and a liquid nitrogen output port (11) respectively; the cold head of the refrigerator (3) is also connected to a nitrogen output port (12). The above-mentioned zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment includes the following: S1. Nitrogen preparation: High-purity nitrogen is separated from ambient air using membrane separation technology or PSA pressure swing adsorption technology; S2, Nitrogen liquefaction: High-purity nitrogen is liquefied by cooling the cold head of a refrigeration unit and stored in a liquid nitrogen collection tank; S3, Liquid nitrogen distribution and supply: When the liquid level in the gas phase liquid nitrogen tank is lower than the set lower limit, the liquid replenishment solenoid valve is automatically opened, and liquid nitrogen is distributed to the gas phase liquid nitrogen tank through the gas-liquid separator, and liquid nitrogen replenishment is achieved by gravity flow. S4. Nitrogen recovery and reliquefaction: Nitrogen volatilized in the gas phase liquid nitrogen tank is recovered through the gas collection and return pipeline, temporarily stored and buffered in the gas buffer tank, and then transported to the cold head of the refrigerator for reliquefaction. S5. System Loss Compensation: When the total liquid nitrogen in the system is lost, the output of nitrogen production is increased, and after liquefaction, it is replenished to the liquid nitrogen collection tank to maintain the dynamic balance of the total liquid nitrogen in the system.

2. The zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment according to claim 1, characterized in that: In step S3, the gas-liquid separator integrates temperature, pressure, and level transmitters as well as an automatic control solenoid valve to ensure stable and smooth transport of low-temperature media in the pipeline.

3. The zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment according to claim 1, characterized in that: In step S4, the recovered nitrogen is temporarily stored in a gas buffer tank to buffer pressure fluctuations and ensure the stability and continuity of the reliquefaction process.

4. The zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment according to claim 1, characterized in that: In step S2, the cold head of the refrigeration unit uses a GM refrigeration unit or a pulse tube refrigeration unit, with a liquid nitrogen output of 4-5 L / h, and liquid nitrogen is produced 10-20 seconds after the gas is introduced.

5. The zero-evaporation liquid nitrogen supply method according to claim 1, characterized in that: In step S1, the purity of high-purity nitrogen gas is ≥99.5%, and the output pressure is 0.7-1.0 MPa.

6. The zero-evaporation liquid nitrogen supply method according to claim 1, characterized in that: In step S3, a common pipeline is provided between the liquid nitrogen collection tank and the gas-liquid separator, and a solenoid valve, a pressure sensor and a safety valve are installed in sequence on the common pipeline.

7. The zero-evaporation liquid nitrogen supply method according to claim 1, characterized in that: In step S3, a liquid replenishment solenoid valve is installed on the connecting pipeline between the gas-liquid separator and each gas phase liquid nitrogen tank. Each gas phase liquid nitrogen tank is equipped with an outlet solenoid valve, a pressure sensor and a level gauge. A one-way valve is installed on the gas collection return pipeline of each gas phase liquid nitrogen tank.

8. A zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment according to claim 1, characterized in that: The pipeline used for transporting liquid nitrogen or cryogenic nitrogen gas adopts a vacuum pipeline. The vacuum pipeline includes an inner tube and an outer tube that are coaxial and nested together. The inner tube and the outer tube are connected by a high-vacuum multi-layer heat insulation structure. There are several support members arranged along the axial direction between the outer tube and the inner tube. A vacuum extraction port is opened on the outer tube.

9. A zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment according to claim 1, characterized in that: It also includes an emergency liquid replenishment procedure: in the event of a system failure, direct liquid nitrogen replenishment can be carried out through the reserved liquid nitrogen replenishment interface.

10. A zero-evaporation liquid nitrogen supply method without liquid nitrogen replenishment according to claim 1, characterized in that: It also includes off-peak electricity operation procedures: liquid nitrogen is prepared and stored centrally during off-peak electricity hours and shut down during peak hours.

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