An air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen, and sometimes also argon and other rare inert gases. There are various technologies that are used for the separation process; the most common is via cryogenic distillation.
The cryogenic separation process requires a very tight integration of heat exchangers and separation columns to obtain a good efficiency and all the energy for refrigeration is provided by the compression of the air at the inlet of the unit. In addition to the cryogenic distillation method there are other methods such as Membrane, Pressure Swing Adsorption (PSA) and Vacuum Pressure Swing Adsorption (VPSA).
Cryogenic Separation Process:
After being removed dust and mechanical impurities by the air filter, air is fed to the main air compressor where air will be compressed to the specified pressure. Then the compressed air enters into to the air cooling tower, where it will be cooled via utility water and waste Nitrogen Gas.
2- Purification System
The cooled air will be fed to the two alternative operating MS absorbers, where the H2O, CO2, C2H2, hydrocarbon and other contaminants will be adsorbed. The MS absorbers are alternatively put into use, while one is working, the other is regenerated. The purification system, during regeneration, uses waste nitrogen which comes from Cold Box via Electrical heater.
The purified air will be divided into two flows. First flow is fed to the plate-fin heat exchanger where this flow is cooled by reflux gas, then it is directly fed to the lower column; The Second flow is fed to the boost air compressor where this flow will be compressed at boosted end, and then it will be sent into plate-fin heat exchanger after being cooled, then it will be extracted from the middle part of plate-fin heat exchanger and be sent into expanded end of boost air compressor, after being expanded, it will be sent into upper column to be rectified.
After being preliminary rectified by lower column, the liquid air, pure liquid nitrogen and waste liquid nitrogen will be obtained. After they are super-cooled by liquid nitrogen (LIN)/liquid air in the sub-cooler and throttled, then fed to the upper column.
After being further rectified by the upper column, the liquid oxygen (LOX) will be obtained at the bottom of upper column. The (LOX) will be pressurized by LOX pump and fed to the plate-fin heat exchanger in order to be reheated for evaporation to obtain gas oxygen (GOX).
The LIN will be extracted from top of lower column, and after being sub-cooled by sub-cooler it can get product LIN.