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Process for Krypton and Xenon Recovery in Pumped-LOX ASU Cycles

IP.com Disclosure Number: IPCOM000019390D
Publication Date: 2003-Sep-12
Document File: 4 page(s) / 94K

Publishing Venue

The IP.com Prior Art Database

Abstract

Xenon is recovered from the high pressure column by withdrawing a small stream of heavies-rich crude LOX. When combined with traditional techniques for xenon removal from the LP column, the overall xenon recovery from pumped LOX cycles can be improved substantially.

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Process for Krypton and Xenon Recovery in Pumped-LOX ASU Cycles

Xenon is recovered from the high pressure column by withdrawing a small stream of heavies-rich crude LOX. When combined with traditional techniques for xenon removal from the LP column, the overall xenon recovery from pumped LOX cycles can be improved substantially.

Xenon is typically recovered from a double column air separation plant (producing oxygen) by removing a small liquid stream from the LP column sump that is further purified in a separate distillation column. This scheme produces very high xenon recoveries when the oxygen product is removed from the LP column as a low-pressure vapor. When the oxygen product is withdrawn from the LP column as a liquid, as in pumped LOX cycles, the liquid product flow is typically removed a stage or two above the sump to allow the heavier xenon (and also krypton) to accumulate in the sump liquid. Unfortunately, the xenon and krypton that exit the column with the oxygen product are not recovered and the xenon recovery is reduced to approximately 72%.

The amount of xenon lost in the pumped LOX product stream can be greatly reduced if the amount of xenon entering the low pressure column can also be reduced. This disclosure suggests several methods designed to reduce the amount of xenon that enters the low pressure column and that is, therefore, lost through the pumped LOX product stream. The basic idea is to recover a large fraction of the krypton and/or xenon contained in the vapor air stream fed to the HP column. This may be accomplished by withdrawing most of the liquid descending through the HP column one or two stages above the bottom of the column. This liquid will have the composition of crude LOX and may be used in the usual manner. It will, however, be substantially depleted of heavy components such as krypton, xenon, methane and carbon dioxide. The remainder of the column liquid is then allowed to proceed down the column and to contact the xenon and krypton-containing vapor feed air, thereby stripping these components from the vapor. The small stream of liquid enriched in krypton and xenon becomes the bottoms stream from the HP column and may then be routed to a separate boiling pot for xenon purification. This is shown schematically in Figure 1. If a krypton product is also desired, the boiling pot may be replaced with a small distillation column. The krypton/xenon...