Air Products and Chemicals, Inc.

Vincent Marano, Iii

Harvey L Vines

James W Pervier

Michael A Patterson

A process is described which uses a modified double distillation cycle for rejecting nitrogen from a natural gas stream containing varying amounts of nitrogen, methane, carbon dioxide and ethane-plus hydrocarbons. The natural gas stream is fractionally distilled in the high pressure distillation stage of the double distillation cycle to provide a nitrogen overhead and a bottoms comprising carbon dioxide and ethane-plus hydrocarbons. A sidestream consisting essentially of nitrogen and methane is withdrawn from the high pressure distillation stage as intermediate level feed to the low pressure distillation stage of the double distillation cycle. The nitrogen overhead from the high pressure stage is cooled by heat exchange with the methane bottoms of the low pressure stage which methane bottoms acquires an extra degree of refrigeration from a methane heat pump cycle to provide extra nitrogen reflux to thoroughly remove the carbon dioxide from the natural gas stream in the high pressure stage.

Nitrogen rejection from natural gas with CO.sub.2 and variable N.sub.2

A process is disclosed for rejecting nitrogen from a natural gas feed containing nitrogen over a wide range of compositions, e.g. 5-85% nitrogen by volume, under elevated pressure using a single distillation column and a closed loop methane heat pump which reboils and refluxes the column. An intermediate reflux condenser is refrigerated by both the heat pump and overhead nitrogen fraction from the distillation column. The process can handle feeds with increasing nitrogen content and more than 100 ppmv carbon dioxide. The feed can be at pipeline pressure with the natural gas liquid components still present or at lower pressure with natural gas liquids removed. A mixed cryogenic refrigerant can be used in the heat pump as an alternative to methane. The process provides a high methane recovery over the entire feed range, and provides a nitrogen product stream having an elevated pressure suitable for recycling and reinjection to an oil or gas well to improve well head pressure.

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Macungie, PA, United States of America

Vincent Marano, Iii