PURPOSE: To obtain ultrahigh purity nitrogen by a method wherein in the lower part of a rectifying column a low-boiling point component and a high-boiling point component are removed from nitrogen; high purity liquid nitrogen is drawn out from the intermediate level of the lower part of the rectifying column and, after being expanded slightly by an expansion valve, injected into the upper part of a rectifying column; and again a low-boiling point component and a high-boiling point component are removed from nitrogen.
CONSTITUTION: The liquid nitrogen at the top of the lower part 4 of a rectifying column flows through a rectifying part (c) so that a low-boiling point component is thereby removed; then the product is stored as the high purity liquid nitrogen in the reservoir R1. This high purity liquid nitrogen is expanded slightly by an expansion valve V1 and injected, in part in the form of high purity nitrogen gas and the rest in the form of high purity liquid nitrogen, into the upper part 5 of the rectifying column, more specifically into a section several levels below the apex of the top rectifying part (g). Oxygen-rich liquid air collecting at the bottom (a) of the lower part 4 of the rectifying column is expanded by an expansion valve V2 and drawn into an upper section (h) in the upper part 5 of the rectifying column and used as a cryogen for a vaporizer condenser VC. According to this method ultrahigh purity nitrogen can be obtained by a simple constitution.
YAMAMOTO TAKAO
TOMITA SHINJI
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