Patent ID: 9316434
Filing Date: 2016-04-19
CPC Classification: F25J

Claim Text:
1. A method of producing a liquid nitrogen stream, a gaseous nitrogen stream, a gaseous stream which is rich in helium and a denitrided stream of hydrocarbons from a feed stream which contains hydrocarbons, nitrogen and helium, the method comprising the following steps: expanding the feed stream in order to form an expanded feed stream; dividing the expanded feed stream into a first introduction stream and a second introduction stream; cooling the first introduction stream within an upstream heat exchanger by heat exchange with a gaseous refrigerant stream which is obtained by dynamic expansion in a cooling cycle in order to obtain a first cooled introduction stream; forming a second cooled introduction stream by cooling, using a first downstream heat exchanger, the second introduction stream; introducing the first cooled introduction stream and the second cooled introduction stream into a fractionating column which comprises a plurality of theoretical fractionating stages; tapping at least one reboiling stream and circulating the reboiling stream in the first downstream heat exchanger in order to cool the second introduction stream; tapping, at a bottom of the fractionating column, a bottom stream which forms the denitrided stream of hydrocarbons; tapping, at a head of the fractionating column, a head stream which is rich in nitrogen; reheating the head stream by at least one second downstream heat exchanger in order to form a reheated stream which is rich in nitrogen; tapping and expanding a first portion of the reheated stream in order to form the gaseous nitrogen stream; compressing a second portion of the reheated stream in order to form a compressed, recycled nitrogen stream, and cooling the compressed, recycled nitrogen stream by circulation through the first downstream heat exchanger and/or each second downstream heat exchanger; liquefying and partially expanding the recycled nitrogen stream in order to form an expanded nitrogen rich stream; introducing at least a portion obtained from the expanded nitrogen rich stream into a first separation container; recovering the gaseous head stream from the first separation container in order to form the helium rich stream; recovering the liquid stream from the bottom of the first separation container and separating the recovered liquid stream into a liquid nitrogen stream and a first reflux stream; introducing, as reflux, the first reflux stream into the head of the fractionating column; introducing the nitrogen rich expanded stream upstream of the second downstream heat exchanger into a second separation container positioned upstream of the first separation container and upstream of the second downstream heat exchanger; introducing the head stream from the second separation container successively into the second heat exchanger and into the first separation container, wherein the introducing of the head stream from the second separation container into the first separation container is performed without the head stream being expanded in any expansion device; and introducing, as reflux, at least a portion of the bottom stream of the second separation container into the head of the fractionating column.