The stream of argon fraction extracted from the middle section of the upper column enters the crude argon column I to be rectified to decrease its oxygen content. The reflux for the crude argon column I is the crude liquid argon that is delivered by the liquid pump after being extracted from the bottom of the crude argon column II. The liquid at the bottom of the crude argon column I returns to the upper column for rectification.
The gas extracted from the top of the crude argon column I enters the bottom of the crude argon column II for further separating oxygen and argon, so that the crude argon gas with a content of oxygen ?2 ppm is obtained, which flows back to the crude argon column II as reflux after being condensed into liquid by the crude argon condenser. The cold source of the crude argon condenser is the liquid air extracted from the sub-cooler, which returns to the proper part of the upper column for rectification after heat exchanging with the crude argon gas and being evaporated.