Nitrogen production method

Abstract

A nitrogen production method wherein air is compressed, is removed of water and carbon dioxide contained therein, and is simultaneously cooled to a temperature close to the liquefying point, and the resultant cleaned and cooled air is fed into a rectifying column for rectification so that high purity nitrogen is withdrawn from the rectifying column overhead; and wherein the oxygen-enriched liquid air withdrawn from the rectifying column bottom is expanded and fed into a condensation step wherein it becomes a source of reflux producing cold in the above-mentioned rectifying column, and then a cold is produced by adiabatically expanding the vaporized gas, after which heat exchange with raw air is performed. In this method, there is provided a closed circulating system wherein a circulating gas which is compressed is cooled by heat exchange with a return gas of the circulating gas, and the resultant cooled gas is fed into a reboiler at the bottom of the above-mentioned rectifying column wherein it vaporizes a liquid in the bottom of the rectifying column, and after the compressed circulating gas itself is liquefied through the above described step and expanded, it is fed into the above-mentioned condenser wherein it is vaporized by heat exchange with the high purify nitrogen from the above-mentioned rectifying column, and further the resultant vaporized gas is restored to normal temperature by heat exchange with the above-mentioned compressed circulating gas and is then subjected to recompression for continued circulation.