Cryogenic separation of lean and rich gas streams

Abstract

A process for simultaneously, cryogenically separating natural gas liquids from a lean natural gas stream and a rich natural gas stream; including, compressing the lean gas feed, cooling the compressed lean gas feed, separating the cooled lean gas feed to form a vapor phase and a liquid phase, expanding the vapor phase lean gas feed, separating the expanded vapor phase lean gas feed to form a second vapor phase and a second liquid phase, fractionating the second vapor phase lean gas feed to form a methane-enriched, low pressure bottoms fraction and a nitrogen-enriched, high pressure overhead fraction, flashing a portion of the methane-enriched bottoms fraction and passing the same in countercurrent, indirect heat exchange with the nitrogen-enriched overhead fraction, to cool the same and produce a vapor phase nitrogen-enriched product and a liquid phase reflux for the fractionator, passing the remainder of the methane-enriched bottoms fraction, the flashed methane-enriched bottoms fraction and the vapor phase nitrogen-enriched fraction in countercurrent heat exchange with the lean gas feed, compressing the rich gas feed, cooling the compressed rich gas feed, fractionating the cooled rich gas feed and the liquid phases separated from the lean gas feed to form a methane-enriched overhead fraction and a natural gas liquids bottoms product and combining the methane-enriched overhead with a portion of the methane-enriched bottoms product from the lean gas feed, prior to the passage of the latter in heat exchange with the lean gas feed. The methane-enriched streams are combined, following their use as heat exchange media, to form a pipeline quality natural gas product and the nitrogen-enriched vapor phase can be utilized as a low BTU fuel gas for the plant.