Patent ID: 8528360

Claim:
A method for cooling a natural gas stream and separating the cooled gas stream into various fractions having different boiling points, such as methane, ethane, propane, butane and condensates, the method comprising: cooling the gas stream in at least one heat exchanger assembly; separating the cooled gas stream in an inlet separation tank into a methane enriched fluid fraction and a methane depleted fluid fraction; feeding the methane depleted fluid fraction from the inlet separation tank into a fractionating column in which a methane rich fluid fraction is separated from a methane lean fluid fraction; feeding at least part of the methane enriched fluid fraction from the inlet separation tank into a cyclonic expansion and separation device in which said fluid fraction is expanded and thereby further cooled and separated into a methane rich substantially gaseous fluid fraction and a methane depleted substantially liquid fluid fraction, wherein the cyclonic expansion and separation device operates to recompress said methane rich substantially gaseous fluid fraction to a pressure which is substantially higher than the operating pressure of the fractionating column; feeding the methane rich substantially gaseous fluid fraction directly from the cyclonic expansion and separation device to the at least one heat exchanger assembly to cool the incoming natural gas stream; and feeding the methane depleted substantially liquid fluid fraction from the cyclonic expansion and separation device into the fractionating column for further separation, wherein the methane rich substantially gaseous fluid fraction and feed from a top outlet conduit of the fractioning column are compressed separately in export compressors to an export pressure, wherein the cyclonic expansion and separation device comprises: a) an assembly of swirl imparting vanes for imposing a swirling motion on the methane enriched fluid fraction, which vanes are arranged upstream of a nozzle in which the methane enriched fluid fraction is accelerated and expanded and thereby further cooled such that centrifugal forces separate the swirling fluid stream into a methane rich fluid fraction and a methane depleted fluid fraction and the cyclonic expansion and separation device further comprises an assembly of swirl imparting vanes which protrude in an at least partially radial direction from a torpedo shaped central body upstream of the nozzle, having a larger outer diameter than the inner diameter of the nozzle, or b) a throttling valve, having an outlet section which is provided with swirl imparting means that impose a swirling motion to the fluid stream flowing through the fluid outlet channel thereby inducing liquid droplets to swirl towards the outer periphery of the fluid outlet channel and to coalesce.