Production of nitrogen and oxygen using atmospheric air is a basic technology of air separation that is widely used in industry and medicine.
Blowing in the blast furnaces for the metal production
Blowing pure oxygen in the basic oxygen furnaces for steel production
Welding operations and gas cutting
Industrial nitrogen and oxygen are produced using liquid air that is separated by rectification method. The air used to produce nitrogen must be pure, free of dust, moisture, carbon dioxide, nitrogen oxides, acetylene and other impurities.
Separating cryogenic plants operate on the principle of air liquefaction. At first, air is compressed by compressor, then it goes thought the heat exchanger and expands in the turbo-expander. As a result, cooled air turns into liquid. Oxygen and nitrogen are separated due to the different boiling points. This process numerously repeats on the special sieve trays and ends with the production of pure liquid oxygen, argon, nitrogen.
This method is mostly effective for the large enterprises because of large size of the system and complexity of its start-up and maintenance. Advantage of this method is that it is possible to produce nitrogen and oxygen of the highest purity, both liquid and gaseous and in any quantity. At the same time, energy consumption for production of 1L of substance is 0,4-1,6 kWh (depending on the technological scheme).
Air is gradually cooling to the low temperatures for freezing-out water vapor, carbon dioxide and air liquefaction.
Process ends with the liquid air liquefaction in the double rectification column.
As a result of rectification, nitrogen vapors containing 99,8-99,99% N2 is extracted in the top of the column, and liquid or vaporous oxygen containing 90-99,5% O2 is removed from the bottom of the column.
Contained in oxygen argon and other inert gases removed with nitrogen and oxygen; in some plants these gases can be extracted.
Production of nitrogen and air relies to the big amount of oxygen that is known to be used for metal welding and cutting, for the intensification of processes in metal and chemical industry and other purposes. When producing large amount of oxygen, production can be made cheaper by using low pressure plants (6-6,5 at) with regenerators and turbo expanders.
In modern plants processing 50 000 and more m3 of air per hour energy consumption is 0,43-0,47 kWh per 1m3 of gas oxygen, what is more, oxygen purity is up to 99,5%, and nitrogen purity can be 99,99%.
Supplementary columns can provide extraction of rare gases (argon, neon and others).