The pry mounted fully automatic liquid nitrogen unit is a modular equipment that integrates air compression, nitrogen oxygen separation, nitrogen liquefaction, and storage and transportation. Its structural principle is based on pressure swing adsorption (PSA) technology and cryogenic liquefaction process. Through highly integrated pry mounted design, it achieves efficient, stable, and safe liquid nitrogen production. The following analysis will be conducted from two aspects: structural composition and working principle:
1、 Structural composition: Modular integrated design
Air handling system
Compressor: A reciprocating or screw compressor is used to compress ambient temperature and pressure air to 0.7-1.0MPa, providing pressure conditions for subsequent separation.
Purification device: including dust filter, oil filter, and freeze dryer, to remove moisture, oil, and particulate matter from the air, ensuring that the purity of the air entering the adsorption system is ≥ 99.9%.
Nitrogen oxygen separation system
Adsorption tower: Equipped with high-quality carbon molecular sieves, it utilizes the difference in diffusion rate between oxygen and nitrogen in micropores (oxygen diffusion rate is much higher than nitrogen) to adsorb oxygen and enrich nitrogen under pressure.
Double tower cycle structure: The alternating adsorption and regeneration of two towers are controlled by PLC program. When one tower produces nitrogen, the other tower depressurizes and desorbs oxygen, achieving continuous and stable gas supply.
Nitrogen liquefaction system
Air cooled oil-free circulating compressor: further compresses and cools the separated nitrogen gas to provide conditions for liquefaction.
Cryogenic mixed refrigerant throttling refrigeration machine: Based on a regenerative multi-component mixed refrigerant throttling refrigeration cycle, low temperature is obtained by compressing and expanding helium gas, and nitrogen gas is cooled to -196 ℃ for liquefaction.
Duwa tank: double-layer vacuum insulation structure, inner layer made of 304 stainless steel (thickness 8mm), outer layer made of Q235 steel, filled with pearl sand insulation material in the middle, vacuum degree ≤ 5 × 10 ⁻ Pa, daily evaporation rate ≤ 0.5%, used for storing liquid nitrogen.
Transportation and Control System
Piston type low-temperature pump: The pump head is made of copper nickel alloy, with a speed of 1500r/min. It can stably output liquid nitrogen at -196 ℃, with a rated flow rate of 500L/h and a maximum head of 80m.
Explosion proof control cabinet: Integrated 7-inch touch screen and PLC module, real-time display of tank pressure, liquid level, and infusion flow rate, response time ≤ 1 second, liquid level control accuracy ± 5mm, pressure control accuracy ± 0.02MPa.
Safety devices: including a safety valve (with a popping pressure of 1.0MPa and a reseating pressure of 0.9MPa), an online purity analyzer (which automatically alarms when the purity is below 99.999%), and a helium leak detection system (with a leakage rate ≤ 1 × 10 ⁻⁹ Pa · m ³/s).
skid-mounted base
Made of Q235 carbon steel welding, with dimensions of 4m × 2.5m × 0.5m, and equipped with four universal wheels capable of bearing 10 tons at the bottom (with the rim wrapped in low-temperature resistant rubber) for easy movement and positioning.
2、 Working principle: Collaborative pressure swing adsorption and cryogenic liquefaction
Air compression and purification
After being pressurized to 0.7-1.0MPa by a compressor, the ambient temperature air passes through a dust filter, an oil filter, and a freeze dryer in sequence to remove moisture, oil, and particulate matter, ensuring air purity.
Nitrogen oxygen separation (PSA process)
Pressure adsorption: The purified compressed air enters the adsorption tower, and the carbon molecular sieve preferentially adsorbs oxygen, while nitrogen is enriched in the gas phase.
Reduced pressure desorption: When the adsorption tower approaches saturation, the adsorbed oxygen is desorbed by reducing the pressure to atmospheric pressure, achieving molecular sieve regeneration.
Twin tower cycle: PLC program controls the alternating adsorption and regeneration of two towers to ensure continuous gas production.
Nitrogen liquefaction (cryogenic process)
Compression cooling: The separated nitrogen gas is further compressed and cooled by an air-cooled oil-free circulation compressor.
Cryogenic refrigeration: Nitrogen enters the cryogenic mixed working fluid throttling refrigeration machine, and is compressed and expanded by helium to obtain low temperature, cooling the nitrogen to -196 ℃ for liquefaction.
Liquid nitrogen storage: Liquefied nitrogen is collected in a Dewar tank and reduced by evaporation loss through a vacuum insulation layer.
Liquid nitrogen transportation and control
Low temperature pump delivery: The plunger type low-temperature pump delivers liquid nitrogen from the Dewar tank to the cooling point, with a stable pressure of 0.7 MPa.
Intelligent monitoring: The explosion-proof control cabinet monitors the pressure, liquid level, and infusion flow of the storage tank in real time, automatically adjusts operating parameters, and ensures safety and efficiency.
3、 Technical advantages and application scenarios
technical advantage
Efficient and energy-saving: The combination of PSA process and cryogenic liquefaction results in high gas production efficiency and low energy consumption (the production cost of liquid nitrogen is only one-third of that of transporting liquid nitrogen).
Stable and reliable: The dual tower circulation structure and PLC automatic control achieve continuous and stable gas supply with low failure rate.
Modular design: The modular structure is easy to transport and install, and only requires pipeline and electrical connections to be used on site.
Safety and environmental protection: Explosion proof control cabinets, safety valves, and online purity analyzers ensure safe operation, and closed systems reduce the risk of nitrogen leakage.
Application scenarios
In the field of chemical engineering, provide a cold source for low-temperature reaction vessels and stably control the reaction temperature (such as -80 ℃± 2 ℃).
Medical field: Provide liquid nitrogen cooling for superconducting magnets in magnetic resonance imaging (MRI) equipment to ensure that the magnets are in a superconducting state.
Metal processing: used for deep cryogenic treatment of bearings to improve hardness (HRC3-5 degrees) and wear resistance.
Research experiment: Provide high-purity liquid nitrogen for physics and chemistry experiments, and support low-temperature environment simulation.