Process for producing ultrapure nitrogen

Abstract

For producing ultrapure nitrogen by low-temperature fractionation of air in a rectification system having at least one rectification column, compressed and purified feed air is conducted into a high pressure column, an oxygen-free pressurized nitrogen fraction is produced from the high pressure column, conducted into a low-pressure column and in the low-pressure column carbon-monoxide-free low-pressure nitrogen is produced as overhead gas. The oxygen-free pressurized nitrogen fraction (,) is either taken off in the liquid state from an upper region of the high pressure column or is provided from a liquid tank (,) containing stored oxygen-free nitrogen and the oxygen-free pressurized nitrogen fraction (,) is expanded into the bottom-heated low-pressure column (,). Ascending vapour in the lowpressure column (,) by mass transfer with and an ultrapure nitrogen reflux applied at the top of the low-pressure column (,) and is freed from carbon monoxide using ultrapure nitrogen, withdrawn as carbon-monoxide-free overhead gas (,) at the top of the low-pressure column (,). After a pressure increase the overhead (,), is partially liquefied, and the liquefied part (,) is expanded into a bottom-heated He—Ne—H,column (,) from which the ultrapure nitrogen (,) is withdrawn in the liquid state.