The core purpose of cryogenic air separation unit is to separate oxygen, nitrogen, argon and other components in the air. Air liquefaction is an essential link in the production of air separation. All air separation distillation and separation processes are based on liquid air.
The boiling points of air components are different, with the boiling points of nitrogen at -195.8 ℃ and oxygen at -183 ℃ under normal pressure, and there is a difference between the two boiling points. In the gaseous state, oxygen and nitrogen molecules are evenly mixed, and hierarchical purification cannot be achieved by boiling point difference. Only when air is deeply refrigerated and liquefied to form a gas-liquid two-phase system, can low-temperature distillation be carried out relying on the boiling point difference. The gas and liquid in the distillation column exchange heat repeatedly, the low boiling point nitrogen continues to vaporize and rise, and the high boiling point oxygen continues to condense and sink, finally separating high purity nitrogen and oxygen.
At the same time, after air liquefaction, the volume is reduced to 1/800 of the original, the specification of distillation column and heat exchange pipeline equipment is greatly reduced, and the equipment investment and operation energy consumption are effectively controlled. The cryogenic liquid medium can also store the cooling capacity, ensure the stable working condition of the device when the load fluctuates, realize the recycling of the cooling capacity of the system, and reduce the overall refrigeration energy consumption.
In addition, air liquefaction is also the premise of extracting rare gases such as argon, neon and helium. At the same time, it can directly produce liquid oxygen and liquid nitrogen products, which is convenient for storage and transportation and emergency gas supply. To sum up, air liquefaction is the core premise of air separation gas and the key process step to ensure the efficient, stable and low-cost operation of the unit.
