Abstract: This invention relates to a method for mixing a lower pressure gas stream into a higher pressure gas stream to achieve a product gas stream which is at the pressure of the higher pressure gas stream. The invention uses a membrane to accomplish what typically is accomplished with a compression step prior to mixing.

Abstract: A process is set forth for the recovery of methane, nitrogen and natural gas liquids (C.sub.2+) from a natural gas feed stream wherein the recovery can be made at high pressure by the integration of a nitrogen rejection stage including a heat pump driven distillation column and a natural gas liquids stage. Nitrogen can be rejected over a wide range of nitrogen concentration (approximately 1 to about 80%) of the feed stream.

Abstract: A method is disclosed for cooling, condensing and subcooling a substantially single component gas stream by passing the gas stream through a heat exchange relationship with a vaporizing multicomponent stream so that carry-up of the condensed liquid phase is maintained without condensed phase backmixing and pot-boiling of the coolant stream is avoided. The single component gas stream is passed through a cold-end up heat exchanger having a serpentine pathway for the gas stream comprising a series of horizontal passes separated by horizontal dividers and alternatingly connected by turnaround passes at each end. The method is particularly applicable to the condensing of a recycle methane stream in a nitrogen rejection process which uses a methane heat pump cycle to provide refrigeration.

Abstract: A method is disclosed for cooling a multicomponent gas stream containing variable amounts of the components by passing the gas stream through a heat exchange relationship with a fluid coolant stream so that carry-up of the condensed phase is maintained without condensed phase backmixing over the compositional range of the multicomponent gas stream. The gas stream is cooled by passing it through a cold-end up heat exchanger having a serpentine pathway for the multicomponent gas stream comprising a series of horizontal passes separated by horizontal dividers and alternatingly connected by turnaround passes at each end, the cross-sectional area of at least one horizontal pass nearer the cold-end being less than the cross-sectional area of a horizontal pass nearer the warm-end. The method is particularly applicable to cooling a natural gas feed stream having a variable nitrogen content in a nitrogen rejection process.

Abstract: 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.

Abstract: 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.