The detail production process of producing industrial oxygen is presented as follows. First, air is drawn from atmosphere through Suction Air Filter to prevent dust from getting into the system. The air is then compressed in a four stage Air Compressor. Air Compressor has inter-coolers between stages and an After-Cooler after 4th stage. Then compressed air, cooled in evaporation cooler will enter into a Moisture Separator. After this the air will pass through an additional cooler called Chilling Unit. Then the air will pass through Oil Absorber where the Oil Vapor carried over from Air Compressor will be removed.
The air then enters one of the Molecular Sieve Vessels/battery. The moisture and carbon dioxide in the air will be removed in this drier. The dry air is again filtered in a Dust Filter before entry to Cold Box to avoid any dust entry to Cold Box. The compressed air, cooled to about 15 to 20 Co free of moisture and carbon dioxide will enter the Cold Box. It initially passes through a Heat Exchanger where the incoming air will be cooled by the outgoing Oxygen and Nitrogen. The air will be cooled to around 100 Co. The air will then be into two streams. The main air stream will enter Expansion Engine at 40 Kgs./Cm2 and will be expanded to 5 Kgs./Cm2 and 150 to 160 Co the rest of the air will pass through Heat Exchanger to be cooled to about 160 Co by the outgoing Oxygen and Nitrogen. This air will then be expanded by an Expansion Valve to form liquid air. Both the air streams will now enter bottom portion of the Lower Column. Operating pressure of the column is around 40 kg/cm2 under normal operating conditions.
As the air enters the Lower Column, after the Expansion Engine and after Expansion Engine valve, a part of this air condenses into liquid and falls at the bottom of the column. This liquid is about 40% Oxygen and 60% Nitrogen and is usually called the “Rich Liquid” and as Nitrogen is more volatile it rises to top of the lower column where it gets cold from the condenser and become liquefied.
Final separation of the two fractions is achieved in the upper column. Both of the poor liquids are carried into the upper column by two Expansion Valves and the pressure drops in the upper column. The rich liquid enters the middle of the Upper column and as it flows down, Nitrogen evaporates and Oxygen continues as liquid. The Liquid Nitrogen (Poor Liquid) enters the top of the column and as it flows down the column, it comes in contact with any evaporating Oxygen and condenses the same into liquid, while the Nitrogen itself becomes a Gas as it is more volatile.
This process takes place in each Gas as it is more volatile. This process takes place in each tray. The entire gaseous Nitrogen is piped out from the top of the column through Heat Exchangers. Similarly the Liquid Oxygen at the bottom of the column is carried away to a Liquid Oxygen Pump from which it is compressed and again passed through the Heat Exchangers into the Gas Cylinders in the cylinder filling station. As the Liquid Oxygen travels through the Heat Exchangers, it evaporates into gaseous oxygen filling the cylinder with gas and giving up its cold to the incoming air. Generally the purity of Oxygen will be 99.5% when the plant is operated exclusively for oxygen production.
The alternative technological option makes use of what is commonly known as the ‘Linde Process”. This method employs an elaborate and complex process which requires highly skilled engineers and workers to separate oxygen from air.