The Boc Group, Inc.

Robert Owen

Robert A Mostello

John Douglas Oakey

Graeme John Dunn

David J Kamrath

In order to provide `ultra high purity` nitrogen having diminished concentrations of light and heavy impurities in comparison with nitrogen produced by conventional cryogenic air separation, the nitrogen product from a conventional cryogenic air separation column is introduced into the bottom of a liquid-vapor contract column 2 fitted with a condenser 8 to provide reflux. A liquid nitrogen stream having a reduced concentration of heavy impurities is withdrawn from the column 2 through an outlet 22 situated at a level a few trays below the top tray in the column 2. The liquid nitrogen is then subjected to two stages of flash separation. In the first stage the liquid is passed through valve 24 into a phase separator 26. In the second stage, the resulting liquid from the first stage, having a reduced concentration of light impurities, is passed through valve 32 into a phase separator 34. Liquid nitrogen product is withdrawn from the phase separator 34 through outlet 38.

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Guildford, United Kingdom

Robert Owen