The principle of liquid nitrogen generation equipment

The principle of liquid nitrogen generator equipment is mainly based on air separation and cryogenic liquefaction technology, which uses physical methods to separate nitrogen from other gases in the air and cool it to liquid state.

I. Basic principles

1. Air compression and pretreatment

The equipment inhales air from the environment, passes through filters, multi-stage compressors and molecular sieve adsorption towers, pressurizes the filtered air, and removes impurities such as moisture, carbon dioxide, and hydrocarbons

2. Cooling and liquefaction

The high-pressure air passes through a heat exchanger, expander or throttle valve, rapidly expands and decompresses, and the temperature drops sharply to -150℃~-196℃, liquefying the nitrogen

Key physical effects: Joule-Thomson effect, reverse Carnot cycle

3. Distillation separation

The liquefied air enters the cryogenic fractionation tower, and the boiling point difference between oxygen and nitrogen (oxygen: -183℃, nitrogen: -196℃) is used for separation

4. Storage and recovery

The separated liquid nitrogen can be transported to a vacuum insulated Dewar tank, and the gaseous nitrogen returns to the heat exchanger

II. Two mainstream types of liquid nitrogen generation equipment

1. Cryogenic air separation equipment (deep cooling method)

Suitable for industrial-grade large-scale liquid nitrogen production (daily output of several tons to hundreds of tons)

Features:

1) Continuous operation is required, and the startup time is long

2) High separation efficiency, purity can reach 99.999%

3) High energy consumption, relying on large compressors and expanders

2. Low-temperature refrigeration cycle equipment (such as Stirling refrigerators, GM refrigerators)

Suitable for small-scale needs such as laboratories and medical treatments (daily output of tens to hundreds of liters)

Features:

1) Stirling cycle: Helium is used as a working fluid to generate low temperature through a compression-expansion cycle

2) Gifford-McMahon (GM) cycle: The cold head moves periodically, and deep cooling is achieved with helium compression (as low as -269℃)

3) Small size, fast startup, but limited refrigeration capacity of a single machine

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