Method for producing liquid and gaseous nitrogen streams, a helium-rich gaseous stream, and a denitrogened hydrocarbon stream

摘要

Disclosed is a process for producing a liquid nitrogen stream (18), a gaseous nitrogen stream (16), a gaseous stream (20) which is rich in helium and a denitrided stream (14) of hydrocarbons from a feed stream which contains hydrocarbons, nitrogen and helium, the process comprising the following steps: - expanding the feed stream (12) in order to form an expanded feed stream (70); - dividing the expanded feed stream (70) into a first introduction stream (72) and a second introduction stream (74); - cooling the first introduction stream (72) within an upstream heat exchanger (28) by heat exchange with a gaseous refrigerant stream (130) which is obtained by dynamic expansion in a cooling cycle (30) in order to obtain a first cooled introduction stream (76);- cooling the second introduction stream (74) by means of a first downstream heat exchanger (52) in order to form a second cooled introduction stream (80); - introducing the first cooled introduction stream (76) and the second cooled introduction stream (80) into a fractionating column (50) which comprises a plurality of theoretical fractionating stages; - tapping at least one reboiling stream (84) and circulating the reboiling stream (84) in the first downstream heat exchanger (52) in order to cool the second introduction stream (74); - tapping, at the bottom of the fractionating column (50), a bottom stream (86) which is intended to form the denitrided stream (14) of hydrocarbons; - tapping, at the head of the fractionating column (50), a head stream (90) which is rich in nitrogen; - reheating the head stream (90) which is rich in nitrogen by means of at least one second downstream heat exchanger (54, 56) in order to form a reheated stream (92) which is rich in nitrogen; - tapping and expanding a first portion (94) of the reheated stream (92) which is rich in nitrogen in order to form the gaseous nitrogen stream (16);- compressing a second portion (96) of the reheated stream (92) which is rich in nitrogen in order to form a compressed, recycled nitrogen stream (100), and cooling the compressed, recycled nitrogen stream (100) by means of circulation through the first downstream heat exchanger (52) and the or each second downstream heat exchanger (54,56);- liquefying and partially expanding the recycled nitrogen stream (100) in order to form an expanded nitrogen rich stream (106); - introducing at least a portion (106; 146) obtained from the expanded nitrogen rich stream (106) into a first separation container (60);- recovering the gaseous head stream from the first separation container (60) in order to form the helium rich stream (20);- recovering the liquid stream (110) from the bottom of the first separation container (60) and separating that liquid stream (110) into a liquid nitrogen stream (18) and a first reflux stream (114); - introducing the first reflux stream (114) as reflux into the head of the fractionating column (50).