Single-double tower switching process and system for high-purity preparation

Abstract

The invention relates to a single-double tower switching system for high-purity preparation and a process thereof, and aims to improve the nitrogen extraction efficiency and meet the gas supply requirements under different load working conditions. The system comprises a tower C1 and a tower C2 which are arranged in parallel, are connected with each other through a pipeline, and are provided with a valve and a liquid nitrogen pump so as to realize efficient gas separation and backflow. When the load exceeds 1600 Nm < 3 > / h, a double-tower double-condensation process is adopted, after air filtration, compression, cold drying and purification treatment, compressed air participates in liquid nitrogen separation and rectification, oxygen-enriched air passes through an expansion machine and then returns to the system, cyclic utilization is achieved, and the nitrogen yield is increased. And when the load is lower than 1500Nm < 3 > / h, the system is switched to a single-tower condensation process, and the C1 tower operates independently, so that stable supply of nitrogen is ensured. By means of the mode, the device can continuously and stably work within the adjusting range of 650 Nm < 3 > / h-4000 Nm < 3 > / h, and the requirement for continuous and stable gas supply in the industries of downstream photovoltaic cells, lithium batteries and the like is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-purity nitrogen preparation, and in particular relates to a single-tower and double-tower switching process and system for high-purity preparation. Background Art

[0002] Regarding the conventional process flow of high-purity nitrogen production equipment, in KDN-2000Nm 3 / h or less is prepared by a single-tower process, which has good stability, but has technical defects such as a large load adjustment range, high energy consumption, and an extraction rate of 50%; KDN-2000Nm 3 / h or more, a double-tower process is used. This method can increase the extraction rate, but it reduces the load to less than 1500Nm 3 / h, the system cannot work. In summary, the traditional single-tower and double-tower production processes cannot adjust the load production. Therefore, the disadvantage is that it cannot be widely used in photovoltaic cells, lithium batteries, carbon fiber crystals, semiconductors, and new energy materials industries.

[0003] The above information disclosed in the above background technology section is only used to enhance the understanding of the background technology of the technology described in this article. Therefore, the background technology may contain certain information that does not form the prior art known in this country to those skilled in the art. Summary of the invention

[0004] In order to solve the defects of the above-mentioned prior art, the present invention proposes a single-double tower switching process and system for high-purity preparation, which integrates the double tower and the single tower into a system, adopts the process flow of switching between the single and double towers, and enables the device to be operated at 1600Nm 3 / h or more, the double-tower double-condensation process is used, at 1500Nm 3 / h or less, use the single tower process, through the above method, not only can the device meet the 650Nm 3 / h-4000Nm 3 It can work continuously and stably within the / h adjustment range, and also meets the needs of continuous and stable gas supply in downstream photovoltaic cells, lithium batteries and other industries.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A single-tower and double-tower switching system for high-purity preparation, comprising:

[0007] The C1 tower and the C2 tower are arranged in parallel, the upper part of the C1 tower is connected with the top of the C2 tower through pipeline I, and valve I is arranged on pipeline I. The upper part of the C2 tower is connected with the top of the C1 tower through pipeline II, and a liquid nitrogen pump is arranged on pipeline II; the lower part of the C1 tower is connected to the gas supply system through pipeline III and the top of the C2 tower is connected to the gas supply system through pipeline IV, the top of the C1 tower is connected with the lower part of the C2 tower through pipeline V, and valve II is arranged on pipeline V; the nitrogen outlet of the upper part of the C1 tower is directly connected to the user end through pipeline VI.

[0008] Furthermore, the air supply system includes an air filter, an air compressor, an air dryer, an air purification system and a plate heat exchanger which are sequentially connected by pipelines.

[0009] Furthermore, the plate heat exchanger is connected to pipeline III, pipeline IV and pipeline VI respectively.

[0010] Furthermore, the air purification system includes two molecular sieve adsorbers arranged in parallel, and electric heating devices respectively connected to the two molecular sieve adsorbers, one end of the two molecular sieve adsorbers is connected to the air dryer pipeline, and the other end is connected to the plate heat exchanger pipeline; one end of the electric heating device is connected to the plate heat exchanger through pipeline IV, and the other end is respectively connected to the two molecular sieve adsorbers pipelines.

[0011] Furthermore, the pipelines I and II contain pure nitrogen, the pipelines III and V contain compressed purified air, the pipeline IV contains oxygen-enriched air, the pipeline VI contains reverse flow nitrogen, and the pipeline VII contains exhaust gas.

[0012] Furthermore, one end of the air filter is an air inlet, and the molecular sieve adsorber is provided with an exhaust gas outlet, and the exhaust gas outlet is connected to a pipeline VII for discharging exhaust gas.

[0013] Another aspect of the present invention further provides a single-tower and double-tower switching process for high-purity preparation based on the above system, comprising the following steps:

[0014] 1600Nm 3 Under load conditions above / h, use double-tower double-condensation process:

[0015] S1: The air passes through the air filter to remove large particles of impurities;

[0016] S2: Enter the air compressor to compress the air to 0.75MpaG;

[0017] S3: Enter the air dryer for cooling and drying, remove some free water in the compressed air and cool it down to 8-12 degrees;

[0018] S4: Enter the air purification system for purification treatment to further remove free water, dust and debris in the compressed air;

[0019] S5: The compressed air is cooled by the plate heat exchanger and then enters the C1 tower and the C2 tower through pipeline III to participate in the separation and distillation of liquid nitrogen;

[0020] S6: The oxygen-enriched air output from tower C2 is expanded by the air expander on pipeline IV and then passes through the plate heat exchanger;

[0021] S7: Liquid nitrogen is extracted from the top of the C1 tower and sent to the top of the C2 tower through valve I on pipeline I, and then the liquid nitrogen is extracted from the top of the C2 tower and returned to the C1 tower through the liquid nitrogen pump on pipeline II. After two cycles to improve the nitrogen extraction rate, the nitrogen product is extracted from the top of the C1 tower and sent to the plate heat exchanger through pipeline VI;

[0022] S8: The compressed air in pipeline III, the oxygen-enriched air in pipeline IV and the nitrogen product in pipeline VI act together in the plate heat exchanger. The compressed air enters the C1 tower after being cooled. The nitrogen product is directly delivered to the user terminal for use after heat exchange.

[0023] 1500Nm 3 / h or less, using a single tower condensation process:

[0024] S9: By closing valve I, valve II and the liquid nitrogen pump, the connection between tower C1 and tower C2 is cut off, and only tower C1 is operated. The nitrogen product is taken out from the top of tower C1, passes through the plate heat exchanger, and is directly sent to the user terminal.

[0025] Furthermore, the oxygen-enriched air in pipeline IV passes through a plate heat exchanger and is then heated by an electric heater, and then input into a molecular sieve adsorber for filtration treatment. After the treatment, the air is discharged into the air through pipeline VII.

[0026] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0027] In general, compared with the prior art, the single-tower and double-tower switching system provided by the present invention can achieve a high torque of 1600Nm by reasonably configuring the single-tower and double-tower switching system. 3 / h or more, the double-tower double-condensation process is used, at 1500Nm 3 / h or less, using a single tower condensation process, it is allowed that when tower C1 or tower C2 is in operation, the other tower is in standby state. Through the above method, not only can the device meet the requirements of 650Nm 3 / h-4000Nm 3 It can work continuously and stably within the / h adjustment range, and also meets the needs of continuous and stable gas supply in downstream photovoltaic cells, lithium batteries and other industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0029] Figure 1 It is the architecture diagram of the single-dual tower switching system in the present invention. DETAILED DESCRIPTION

[0030] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application usually described and shown in the drawings here can be arranged and designed in various configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0031] Embodiment 1:

[0032] This embodiment provides a single-tower and double-tower switching system for high-purity preparation, see Figure 1 ,include:

[0033] C1 Tower and C2 Tower: C1 Tower and C2 Tower are arranged side by side to form an efficient gas separation unit;

[0034] Pipeline I: The upper part of the C1 tower is connected to the top of the C2 tower through pipeline I. Pipeline I is provided with valve I for controlling the flow direction of nitrogen;

[0035] Pipeline II: connects the upper part of tower C2 with the top of tower C1, responsible for transporting the pure nitrogen produced by tower C2 to circulate to tower C1. A liquid nitrogen pump is installed on pipeline II to ensure the pressure and speed of gas flow;

[0036] Pipeline III: connected to the lower part of tower C1, inputs compressed purified air to ensure the quality of raw gas;

[0037] Pipeline IV: connects the top of tower C2 with the gas supply system, inputs oxygen-enriched air, and participates in the nitrogen separation process;

[0038] Pipeline V: connects the top of tower C1 with the bottom of tower C2 to realize air circulation. Valve II is set on pipeline V to control the flow of gas;

[0039] Pipeline VI: The nitrogen outlet at the top of the C1 tower is directly connected to the user end through pipeline VI to provide high-purity nitrogen products;

[0040] Pipeline VII: The exhaust gas outlet in the system is connected to pipeline VII, which is used to discharge the treated exhaust gas to ensure compliance with environmental protection standards.

[0041] In a further embodiment, the air supply system includes an air filter, an air compressor, an air dryer, an air purification system and a plate heat exchanger which are sequentially connected by pipelines.

[0042] Air filter: As the starting part of the system, one end of the air filter is the air inlet, which is responsible for removing solid particles and impurities in the air to ensure the quality of air entering subsequent equipment.

[0043] Air compressor: responsible for compressing the filtered air to the required pressure to provide power for the subsequent separation and purification process.

[0044] Air dryer: removes moisture from the air through cooling and condensation processes to prevent moisture from affecting subsequent separation equipment.

[0045] Air purification system:

[0046] The compressed air is further purified by molecular sieve adsorbers.

[0047] Electric heating device: responsible for heating the passing air, improving the adsorption efficiency of the molecular sieve, and ensuring the removal of excess oxygen and moisture.

[0048] Plate heat exchanger: connected to pipeline III, pipeline IV and pipeline VI respectively, responsible for optimizing the temperature of the gas and improving the thermal efficiency of the system.

[0049] Furthermore, the air purification system includes two molecular sieve adsorbers arranged in parallel to achieve higher processing efficiency, and an electric heating device connected to the two molecular sieve adsorbers respectively, which ensures that the electric heating device reaches the best working state during the processing.

[0050] One end of the two molecular sieve adsorbers is connected to the air dryer pipeline, and the other end is connected to the plate heat exchanger pipeline; one end of the electric heating device is connected to the plate heat exchanger through pipeline IV, and the other end is respectively connected to the two molecular sieve adsorbers pipelines.

[0051] Further, pipeline fluid description

[0052] Pipeline I and Pipeline II: Both transmit high-purity nitrogen, which is directly used at the user end or refluxed to the separation system.

[0053] Pipeline III and Pipeline V: flow with compressed purified air to ensure the gas quality during the separation process.

[0054] Pipeline IV: oxygen-enriched air, which participates in the separation of nitrogen after treatment.

[0055] Pipeline VI: Backflow nitrogen to ensure stable operation and efficient separation of the system.

[0056] Pipeline VII: used for exhaust gas discharge, connected to the environmental protection treatment system to ensure that the discharge meets environmental protection requirements.

[0057] System operation principle

[0058] During operation, the air is first processed by an air filter and an air compressor to ensure that the air entering the system is clean and has sufficient pressure. After passing through the cold dryer, the air with reduced humidity enters the molecular sieve adsorber, which uses the molecular sieve's selective adsorption of oxygen to remove the oxygen component in the air. The treated air is then heated by an electric heating device, then temperature-adjusted by a plate heat exchanger, and finally enters the C1 tower and C2 tower for nitrogen separation. The separated high-purity nitrogen is transported to the user end through pipeline VI to ensure timely delivery of the product. The system also has a switching function that enables the device to switch between 40% (1600Nm 3 / h) or more, the double-tower double-condensation process is used, at 1500Nm 3 / h or less, using a single tower condensation process, it is allowed that when tower C1 or tower C2 is in operation, the other tower is in standby state. Through the above method, not only can the device meet the requirements of 650Nm 3 / h-4000Nm 3 It can work continuously and stably within the / h adjustment range, and also meets the needs of continuous and stable gas supply in downstream photovoltaic cells, lithium batteries and other industries.

[0059] In a further embodiment, a PLC (Programmable Logic Controller) system is also provided to realize automatic monitoring and regulation of all valves, pumps and gas flows.

[0060] Real-time data, including parameters such as nitrogen purity, flow, pressure and temperature, are displayed through the human-machine interface (HMI), making it easy for operators to monitor.

[0061] Install a variety of sensors to monitor gas flow, pressure and temperature changes in real time to ensure that the system operates in a safe and stable state.

[0062] An alarm system is set up to automatically sound an alarm and take corresponding measures when an abnormal situation is monitored (such as pressure is too high or too low, nitrogen purity is lower than the set value, etc.).

[0063] In summary, the single-tower and double-tower switching system disclosed in this embodiment can effectively improve the purity and production efficiency of nitrogen through a reasonably configured single-tower and double-tower switching system combined with an efficient gas supply and monitoring system, and meet the needs of various industries for high-purity nitrogen. The system has a high degree of automation, is easy to operate and monitor, and reduces the possibility of human operating errors, thereby improving the safety and reliability of the overall operation.

[0064] Another aspect of the present invention further provides a single-tower and double-tower switching process for high-purity preparation based on the above system, comprising the following steps:

[0065] 1600Nm 3 Under load conditions above / h, use double-tower double-condensation process:

[0066] S1: Air treatment

[0067] The air passes through the air filter to remove large particles of impurities;

[0068] Optionally or preferably, the device uses a high-efficiency filter (such as a HEPA filter) to remove dust and moisture from the air. It is also equipped with a pressure and flow sensor to monitor the air inflow and quality in real time.

[0069] S2: air compression

[0070] Enter the air compressor to compress the air to 0.75MpaG;

[0071] Optionally or preferably, the compressor is a variable frequency driven screw compressor to achieve energy efficiency optimization and flow regulation. And the automatic adjustment function is set to maintain the output pressure at 0.75MpaG.

[0072] S3: Cooling and drying

[0073] Enter the air dryer for cooling and drying, remove some free water in the compressed air and cool it down to 8-12 degrees;

[0074] Optionally or preferably, the air dryer uses a cooling dryer with a temperature controlled at 8-12°C to ensure a moisture removal rate of up to 99%. An automatic drainage device is installed to regularly discharge condensed water in the dryer.

[0075] S4: Air purification

[0076] Enter the air purification system for purification treatment to further remove free water, dust and debris in the compressed air;

[0077] Optionally or preferably, a molecular sieve filter composed of activated carbon and molecular sieve is used to further remove impurities and moisture. The oxygen content and moisture content of the purified air are monitored in real time to ensure that production standards are met.

[0078] S5: Liquid nitrogen separation and distillation

[0079] After the compressed air is cooled by the plate heat exchanger, it enters the C1 tower and the C2 tower through pipeline III to participate in the separation and distillation of liquid nitrogen;

[0080] Optionally or preferably, the C1 tower and the C2 tower adopt high-efficiency fillers or plate designs to improve separation efficiency. Nitrogen coolant is used to ensure that the temperature in the tower is controlled below -150°C.

[0081] S6: Oxygen-enriched air expansion

[0082] The oxygen-enriched air output from tower C2 is expanded by the air expander on pipeline IV and then passes through the plate heat exchanger;

[0083] Optionally or preferably, use a high-efficiency expander equipped with an energy recovery system to improve overall energy efficiency. Set up an automatic control system for the expander to adjust the output according to the real-time load.

[0084] S7: Liquid nitrogen cycle

[0085] Liquid nitrogen is extracted from the top of Tower C1 and sent to the top of Tower C2 through valve I on pipeline I. Liquid nitrogen is then extracted from the top of Tower C2 and returned to Tower C1 through the liquid nitrogen pump on pipeline II. After two cycles to increase the nitrogen extraction rate, the nitrogen product is extracted from the top of Tower C1 and sent to the plate heat exchanger through pipeline VI.

[0086] Optionally or preferably, the liquid nitrogen pump uses a low temperature resistant, high efficiency liquid nitrogen pump to ensure stable liquid nitrogen circulation. The pipeline uses an insulated pipeline to reduce the heat loss of liquid nitrogen during transportation.

[0087] S8: Nitrogen product output

[0088] The compressed air in pipeline III, the oxygen-enriched air in pipeline IV and the nitrogen product in pipeline VI act together in the plate heat exchanger. The compressed air enters the C1 tower after being cooled. The nitrogen product is directly delivered to the user terminal for use after heat exchange.

[0089] Optionally or preferably, a multi-stage valve and flow meter are provided to ensure accurate control of the nitrogen flow rate, and an online analytical instrument is installed to monitor the nitrogen content, oxygen content and moisture content of the nitrogen in real time.

[0090] 1500Nm 3 / h or less, using a single tower condensation process:

[0091] S9: By closing valve I, valve II and the liquid nitrogen pump, the connection between tower C1 and tower C2 is cut off, and only tower C1 is operated. The nitrogen product is taken out from the top of tower C1, passes through the plate heat exchanger, and is directly sent to the user terminal.

[0092] Optionally or preferably, it is equipped with an automatic switching system, using a PLC control system to automatically switch the process mode according to real-time flow and pressure. Valve I and valve II are electric valves to achieve fast switching and reduce system downtime.

[0093] Furthermore, the system is also equipped with operation monitoring:

[0094] Through the SCADA system, key parameters are collected to monitor the system operation status in real time.

[0095] Set alarm thresholds to detect and handle abnormal situations in a timely manner to ensure safe operation.

[0096] System advantages and applications

[0097] Strong load adaptability: This process can be 650Nm 3 / h to 4000Nm 3 / h, greatly improving the continuity and stability of nitrogen production.

[0098] Energy efficiency optimization: Through data analysis and intelligent control, optimize system operation, reduce unnecessary energy consumption, and reduce operating costs.

[0099] Wide applicability: Suitable for photovoltaic, lithium battery, carbon fiber, semiconductor and other industries, meeting their high standards for high-purity nitrogen.

[0100] Furthermore, the oxygen-enriched air in pipeline IV passes through a plate heat exchanger and is then heated by an electric heater, and then input into a molecular sieve adsorber for filtration treatment. After the treatment, the air is discharged into the air through pipeline VII.

[0101] Optionally or preferably, the heat exchanger selects an efficient plate heat exchanger to increase the heat exchange area and efficiency to ensure that the oxygen-enriched air is quickly cooled to the set temperature.

[0102] The fluid flow direction is designed to be countercurrent to maximize heat exchange efficiency.

[0103] Operation parameter setting:

[0104] The hot-end air inlet and return air outlet temperatures of the heat exchanger are set to approximately 8 to 12 degrees, and the cold-end inlet temperature target is below -160 degrees.

[0105] Monitor the temperature sensor for real-time feedback to ensure that the heat exchange effect meets the design standards.

[0106] The heater adopts an electric heater (such as an aluminum alloy electric heater) and has the characteristics of fast response and high efficiency.

[0107] Configure multi-stage heating units to meet heating needs under different loads.

[0108] Heating process control:

[0109] The heating target temperature is set to 165-200 degrees to ensure the best working condition of the molecular sieve adsorber.

[0110] Equipped with a temperature controller to monitor and adjust the heater output in real time to prevent overheating or overcooling.

[0111] The molecular sieve adsorber adopts a double-tower design and operates alternately to improve the reliability and efficiency of the system.

[0112] Filled with high-efficiency molecular sieves, such as 5A or 13X molecular sieves, which have excellent selectivity and adsorption capacity.

[0113] Running parameter settings:

[0114] During startup, monitor the vacuum and pressure of the adsorber to ensure that they are within a reasonable range (usually 0.1-1.0MPa).

[0115] The adsorption time is set to 4-8 hours, depending on the specific operating conditions.

[0116] Emission treatment:

[0117] After treatment, the oxygen-enriched air is discharged into the atmosphere through pipeline VII.

[0118] Configure the emission monitoring system to ensure that the oxygen concentration of the emission meets environmental protection standards.

[0119] It should be noted that the controller and its automatic control program involved in the present invention can be implemented in the scenario of the present invention by those skilled in the art according to the principles of similar control programs in the prior art, and are not the inventiveness of the present invention. In addition, the electronic components and corresponding electronic circuits involved in this application are all prior art, and those skilled in the art can fully implement them. Needless to say, the content protected by the present invention does not involve improvements to software, algorithms and methods.

[0120] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A single-tower and double-tower switching system for high-purity preparation, characterized in that: include: The C1 tower and the C2 tower are arranged in parallel, the upper part of the C1 tower is connected with the top of the C2 tower through pipeline I, and valve I is arranged on pipeline I. The upper part of the C2 tower is connected with the top of the C1 tower through pipeline II, and a liquid nitrogen pump is arranged on pipeline II; the lower part of the C1 tower is connected to the gas supply system through pipeline III and the top of the C2 tower is connected to the gas supply system through pipeline IV, the top of the C1 tower is connected with the lower part of the C2 tower through pipeline V, and valve II is arranged on pipeline V; the nitrogen outlet of the upper part of the C1 tower is directly connected to the user end through pipeline VI.

2. A single-tower and double-tower switching system for high-purity preparation according to claim 1, characterized in that: The air supply system comprises an air filter, an air compressor, an air dryer, an air purification system and a plate heat exchanger which are sequentially connected by pipelines.

3. A single-tower and double-tower switching system for high-purity preparation according to claim 2, characterized in that: The plate heat exchangers are connected to pipeline III, pipeline IV and pipeline VI respectively.

4. A single-tower and double-tower switching system for high-purity preparation according to claim 3, characterized in that: The air purification system includes two molecular sieve adsorbers arranged in parallel, and electric heating devices respectively connected to the two molecular sieve adsorbers, one end of the two molecular sieve adsorbers is connected to the air dryer pipeline, and the other end is connected to the plate heat exchanger pipeline; one end of the electric heating device is connected to the plate heat exchanger through pipeline IV, and the other end is respectively connected to the two molecular sieve adsorbers pipelines.

5. A single-tower and double-tower switching system for high-purity preparation according to claim 4, characterized in that: The pipelines I and II contain pure nitrogen, the pipelines III and V contain compressed purified air, the pipeline IV contains oxygen-enriched air, the pipeline VI contains reflux nitrogen, and the pipeline VII contains exhaust gas.

6. A single-tower and double-tower switching system for high-purity preparation according to claim 5, characterized in that: One end of the air filter is an air inlet, and the molecular sieve adsorber is provided with an exhaust gas outlet, and the exhaust gas outlet is connected to a pipeline VII for discharging exhaust gas.

7. A single-tower and double-tower switching process for high-purity preparation, implemented based on the system described in any one of claims 1 to 6, characterized in that: The steps include: 1600Nm 3 Under load conditions above / h, use double-tower double-condensation process: S1: The air passes through the air filter to remove large particles of impurities; S2: Enter the air compressor to compress the air to 0.75MpaG; S3: Enter the air dryer for cooling and drying, remove some free water in the compressed air and cool it down to 8-12 degrees; S4: Enter the air purification system for purification treatment to further remove free water, dust and debris in the compressed air; S5: The compressed air is cooled by the plate heat exchanger and then enters the C1 tower and the C2 tower through pipeline III to participate in the separation and distillation of liquid nitrogen; S6: The oxygen-enriched air output from tower C2 is expanded by the air expander on pipeline IV and then passes through the plate heat exchanger; S7: Liquid nitrogen is extracted from the top of the C1 tower and sent to the top of the C2 tower through valve I on pipeline I, and then the liquid nitrogen is extracted from the top of the C2 tower and returned to the C1 tower through the liquid nitrogen pump on pipeline II. After two cycles to improve the nitrogen extraction rate, the nitrogen product is extracted from the top of the C1 tower and sent to the plate heat exchanger through pipeline VI; S8: The compressed air in pipeline III, the oxygen-enriched air in pipeline IV and the nitrogen product in pipeline VI act together in the plate heat exchanger. The compressed air enters the C1 tower after being cooled. The nitrogen product is directly delivered to the user terminal for use after heat exchange. 1500Nm 3 / h or less, using a single tower condensation process: S9: By closing valve I, valve II and the liquid nitrogen pump, the connection between tower C1 and tower C2 is cut off, and only tower C1 is operated. The nitrogen product is taken out from the top of tower C1, passes through the plate heat exchanger, and is directly sent to the user terminal.

8. A single-tower and double-tower switching process for high-purity preparation according to claim 7, characterized in that: The oxygen-enriched air in pipeline IV passes through a plate heat exchanger and is then heated by an electric heater before being input into a molecular sieve adsorber for filtration treatment. After treatment, the air is discharged into the air through pipeline VII.

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