| 摘要 |
PURPOSE:To compress the recycle gas in a nitrogen producing device without requiring any expensive oxygen compressor. CONSTITUTION:Product nitrogen gas is produced by rectifying compressed material air in an intermediate pressure rectifying device A (P5). An oxygen-rich liquid produced by rectification is stored in a lower part of the rectifying device A, and after expansion the liquid is supplied as a reflux liquid into an upper part 8 of a low pressure rectifying device B, and then this liquid undergoes another rectification to be separated into a more concentrated oxygen-rich liquid in a lower part of the rectifying device B for use as a cooling source for a condenser 7. A mixed gas is separated which contains oxygen in an amount equal to or lower than that contained in the air which is separated in the upper part 8 of the rectifying device B and, by using this oxygen-poor mixed gas as a recycle gas, an ordinary air compressor can be employed in compression.
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