The air in nature is not absolutely dry, and a certain amount of gaseous water vapor is always mixed inside, which is a conventional part of air. Under normal pressure and normal temperature, water vapor is evenly dispersed in the air and will not condense into liquid water, so we cannot directly observe water.
In the air separation operation, the air is first compressed by the air compressor. After the air is compressed, the volume is greatly reduced, and the density of water vapor in unit space increases sharply. At the same time, the saturated water content of air will change with the increase of pressure. Under high pressure, the upper limit of water vapor contained in air tends to be fixed. When the water vapor content exceeds the saturation value corresponding to the pressure, the air will reach the supersaturated state, which has the basis of water precipitation.
The air compression process will generate a lot of heat, and the high temperature environment can temporarily improve the water holding capacity of air and delay the liquefaction of water vapor. Therefore, the compressed high-temperature air needs to be cooled by the cooling system. As the temperature decreases, the capacity of air to hold water vapor will decrease significantly, which is the core factor of water vapor condensation. If the excess gaseous water vapor in the air cannot be retained, it will undergo phase change, condense from the gaseous state to liquid droplets, and finally precipitate from the air.
This is also the reason why the air separation process must be equipped with drainage and drying devices. Timely removal of the precipitated water can prevent water from entering the subsequent low-temperature equipment, avoid freezing blocking the pipeline and damaging the unit, and ensure the stable operation of the air separation system.
