NITROGEN REJECTION FROM NATURAL GAS WITH CO2 AND VARIABLE N2 CONTENT

摘要

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 A sidestream consisting essentially of nitrogen and methane is withdrawn from the high pressure distillation stage as intermediate level feed to the low pressure distillation stage of the double distillation cycle.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.