How to separate nitrogen and oxygen using an air separation plant: here is the guide that explains this process in detail.
The separation of nitrogen from oxygen is part of the ” air fractionation ” process, which allows obtaining pure nitrogen and oxygen, used in various industrial fields.
Over time, two main approaches to air separation have been developed:
- one based on very low temperatures (cryogenic processes), used for activities requiring large quantities of oxygen,
- and one at room temperature , which uses adsorbent molecular sieves (PSA process) or polymeric membranes.
Separating nitrogen and oxygen essentially means splitting air into its components . This is done primarily through the use of distillation columns , which are located in air liquefaction plants.In this guide, we will explore how nitrogen and oxygen separation occurs using the air separation plant . Here are all the details on the topic.
The distillation columns
Modern air separation plants are characterized by the presence of two distillation columns , each with a different pressure inside them.
One column operates at a pressure ranging between 4 and 5 atmospheres , while the other operates at atmospheric pressure . In the past, systems with simple or double pressure difference columns were also used, while the “Claude process” used a special column called the “Claude column”.
It is important to know that air is composed mainly of nitrogen (N₂), oxygen (O₂) and argon (Ar), as well as traces of other gases such as neon, helium, krypton, hydrogen, xenon and variable amounts of carbon dioxide, which depend on environmental conditions.
The high pressure column
The air is compressed to 200 atmospheres and then fed into the reboiler, where it expands and is channeled to the first column, which operates at 5 atmospheres of pressure. During this phase, the air acts as a heating fluid for the boiler. As the expansion occurs, the gas is partially cooled, but the liquefaction is only partial.
In the high pressure column the distillation process takes place, which separates the air into its main constituents. In particular, the following results are obtained:
- at the bottom of the column: 40% oxygen and 60% nitrogen;
- at the top of the column: 98% nitrogen.
The atmospheric pressure column
The second column is the one at atmospheric pressure, where the separation process continues. Here we obtain:
- at the top of the column : pure nitrogen;
- at the bottom of the column : 95% liquid oxygen.
The two columns, the high-pressure column and the atmospheric-pressure column, are usually superimposed. However, in the latest generation systems, it is possible to separate them, so as to channel the liquid oxygen towards the top of the high-pressure column using pumps.
In the old Claude column plant , the separation process was done by a “return process”, without the use of two separate columns. This approach was less efficient and less controllable than modern plants.
Today, air separation by fractional distillation is the most widely used technique for obtaining high-purity oxygen, especially in industrial processes such as oxyfuel combustion.
