Abstract: A process and apparatus is described for liquefying natural gas using two closed cycle, multicomponent refrigerants wherein a low level refrigerant cools and liquefies the gas by indirect heat exchange and a high level refrigerant cools and partially liquefies the low level refrigerant by indirect multistage heat exchange. The high level refrigerant is phase separated in order to use lighter refrigerant components to perform the final lowest level of refrigeration while the liquid phase of the separation is split and then expanded for refrigeration duty in order to avoid multiple flash separations wherein heavier components are used to provide the lower levels of refrigeration.

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 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.