The Boc Group, Inc.

David J Layland

John T Lavin

An improved process and apparatus for separating air to form oxygen and nitrogen in at least one cryogenic distillation column is disclosed. Nitrogen vapor taken from the colunm is warmed in countercurrent flow to incoming air in a heat exchanger wherein compressed air is being cooled for separation. A portion of the warm nitrogen is compressed, cooled in the heat exchanger and passed through an expansion turbine. The expanded nitrogen is passed through a reboiler associated with the column and further cooled in the heat exchange means. Part of the resulting liquid nitrogen is used to provide reflux for the column and the remainder is taken as product. Preferably, at least a portion of the compressed air stream is expanded in a turbine, passed through the reboiler associated with the column to provide reboil therefor, liquified by heat exchange and introduced to the distillation column through a throttling valve. Further, an argon product can be recovered by withdrawing an argon-rich stream from a distillation column and passing it to a further column for purification. Vapor from the distillation column, or another in a plurality of distillation columns, is used to provide reflux for the further column with the resulting condensed vapor being returned to the column from which it was withdrawn.

Air separation

A process for the separation of air to obtain oxygen, nitrogen and argon is disclosed which comprises: subjecting air from which carbon dioxide and water have been removed to fractional distillation in a first column to form oxygen-nitrogen vapor and argon-enriched oxygen; separating argon from the latter in a second column operating at substantially lower pressure than the first; liquefying a portion of the nitrogen vapor in a cycle including heat exchange with incoming air and compression to a pressure above that of the first column, a portion of the liquid nitrogen being taken as product and a second portion being returned to the first column as reflux. Liquid-oxygen and nitrogen vapor from the first column are mixed in a liquid-vapor contact column, impure liquid nitrogen is withdrawn therefrom and used as reflux in the first column. A remixed oxygen-nitrogen stream is withdrawn from the contact column and expanded to create refrigeration for the system. Also, disclosed is apparatus for carrying out the subject process.

An improved process and apparatus for separating air to form oxygen and nitrogen in at least one cryogenic distillation column is disclosed. Nitrogen vapor taken from the column is warmed in countercurrent flow to incoming air in a heat exchanger wherein compressed air is being cooled for separation. A portion of the warm nitrogen is compressed, cooled in the heat exchanger and passed through an expansion turbine. The expanded nitrogen is passed through a reboiler associated with the column and further cooled in the heat exchange means. Part of the resulting liquid nitrogen is used to provide reflux for the column and the remainder is taken as product. Preferably, at least a portion of the compressed air stream is expanded in a turbine, passed through the reboiler associated with the column to provide reboil therefor, liquified by heat exchange and introduced to the distillation column through a throttling valve. Further, an argon product can be recovered by withdrawing an argon-rich stream from a distillation column and passing it to a further column for purification. Vapor from the distillation column, or another in a plurality of distillation columns, is used to provide reflux for the further column with the resulting condensed vapor being returned to the column from which it was withdrawn.

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Norton, United Kingdom

David J Layland