Air separation is most commonly achieved through refrigeration and distillation. This method is based on the differences in boiling points of different components at different temperatures and uses the principles of condensation and vaporization for gas separation.

Specifically, commonly used air separation methods include the following steps:

1. Compression: Compress air in the atmosphere through a compressor to increase gas density and pressure.

2. Precooling: Pass the compressed air into air coolers (precoolers) to cool it under normal pressure and condense the water vapor in it.

3. Expansion (expander or expansion valve): Pass the cooled gas through the expansion device to reduce both the pressure and temperature.

4. Separation: Pass the expanded gas into a separation device, usually a distillation tower or adsorption column.

    a. Distillation method: Separation using the differences in boiling points of different components in the air. In the distillation column, the temperature is gradually increased, causing the different components to vaporize and condense respectively, thereby separating oxygen, nitrogen and other inert gases.

    b. Adsorption method: Use an adsorbent, such as activated carbon, to selectively adsorb certain components. By changing pressure and temperature, the adsorbent can adsorb and desorb to achieve gas separation.

5. Product collection: After separation, the pure oxygen and pure nitrogen obtained are collected separately for further processing and storage.

This air separation method produces high-purity oxygen and nitrogen for use in many applications such as medical, industrial and scientific research.