Liquid nitrogen preparation production system

The liquid nitrogen preparation production system is a comprehensive low-temperature engineering device based on air separation technology, which extracts, purifies, and liquefies nitrogen from the atmosphere into liquid nitrogen.

　　Liquid nitrogen preparation production systemIt is a comprehensive low-temperature engineering device based on air separation technology that extracts, purifies, and liquefies nitrogen from the atmosphere into liquid nitrogen. As a fundamental equipment in modern industries, scientific research, healthcare, and food processing, the liquid nitrogen preparation system not only ensures a stable supply of high-purity liquid nitrogen, but also significantly reduces the costs, safety, and supply chain risks associated with traditional reliance on external procurement and transportation.

1、 Basic components of the system

A complete liquid nitrogen preparation system typically consists of the following core modules:

Air compression unit: using oil-free or micro oil screw/piston compressors to pressurize ambient air to 5-10 bar, providing a power basis for subsequent separation. Oil free design can avoid oil vapor pollution and ensure the purity of the final product.

Air purification unit: including multi-stage filters (for water, oil, and dust removal), freeze dryer, and double tower molecular sieve adsorber, used for deep removal of impurities such as water, carbon dioxide, hydrocarbons, etc., to prevent them from freezing and blocking pipelines in low temperature range.

Heat exchange and cold recovery unit: The main heat exchanger (such as plate fin or coiled tube) achieves efficient heat exchange between high-pressure air and reflux low-temperature nitrogen, significantly reducing energy consumption and recovering cold energy.

Low temperature separation and liquefaction unit (cold box): integrates distillation tower, throttle valve or turbine expander, condenser evaporator and other components to achieve nitrogen oxygen separation and nitrogen liquefaction at around -196 ℃. This part is usually enclosed in a vacuum insulated cold box to reduce heat leakage.

Liquid nitrogen storage and transportation unit: including built-in or external vacuum insulated Dewar tanks (with capacities ranging from tens of liters to several cubic meters), equipped with level gauges, pressure control valves, and liquid extraction interfaces for users to use as needed.

Automatic control system: Based on PLC or industrial computer platform, it realizes fully automated operation, with functions such as start stop control, parameter monitoring (pressure, temperature, purity, liquid level), fault diagnosis, remote communication (supporting 4G/Wi Fi/Modbus), etc.

Safety protection system: covering multiple safety mechanisms such as oxygen concentration monitoring, overpressure relief, leakage protection, emergency shutdown, etc., to ensure long-term stable and safe operation of the equipment.

2、 Working principle

　　Liquid nitrogen preparation production systemThe core principle is to use the boiling point difference of various components in the air (mainly nitrogen 78%, oxygen 21%) for low-temperature distillation separation. The typical process is as follows:

The ambient air enters the compressor after being filtered and compressed to the required pressure;

After cooling, removing water and oil, compressed air enters molecular sieves for deep drying and CO adsorption;

The purified high-pressure air enters the main heat exchanger and is pre cooled to near liquefaction temperature by the reflux low-temperature nitrogen gas;

Pre cooled air is further cooled by throttling expansion or turbine expansion, and some of the gas is liquefied and enters the distillation tower;

In the distillation tower, low boiling nitrogen is enriched upwards, while high boiling oxygen is discharged downwards, achieving efficient separation;

High purity nitrogen is condensed into liquid at the top of the tower and flows into the storage tank; Unliquefied nitrogen is discharged as reflux gas after participating in heat exchange to achieve energy recovery;

The entire process follows the Linde cycle, Claude cycle, or their improved versions, and some systems also introduce energy-saving technologies such as two-stage expansion and residual cooling utilization.

3、 Main types and scales

According to production capacity, structure, and application requirements, liquid nitrogen preparation systems can be divided into the following categories:

Small system (<100L/day): suitable for laboratories, clinics, and biological sample banks, with small size, low noise, and easy operation.

Medium sized system (100-1000L/day): used in small and medium-sized food factories, electronic manufacturing, hospital central laboratories, often equipped with automatic fluid replacement and remote monitoring functions.

Large scale systems (>1000L/day): serving steel, chemical, liquid nitrogen distribution stations, etc., integrating complete air separation units (ASU), can operate continuously for months or even years.

Skid mounted system: All components are integrated into standard containers or pry blocks for easy transportation, installation, and expansion, suitable for temporary projects or deployment in remote areas.

4、 Key Technologies and Innovation

Efficient molecular sieve regeneration technology: using dual tower alternating adsorption and heating regeneration to ensure continuous purification capacity and extend service life.

Optimization design of turboexpander: improving isentropic efficiency and reducing unit liquid nitrogen energy consumption（*The system can reach below 0.6 kWh/L.

Intelligent control algorithm: dynamically adjust compressor frequency, expander speed, and valve opening based on load forecasting to achieve optimal energy efficiency.

Vacuum multi-layer insulation (MLI) technology: applied to cold boxes and storage tanks, significantly reducing heat invasion and liquid nitrogen evaporation losses (daily evaporation rate can be less than 0.5%).

High purity assurance mechanism: Real time monitoring of nitrogen purity through online oxygen analyzer to ensure output liquid nitrogen purity ≥ 99.999% (5N level).