Process for producing liquid and gaseous nitrogen streams, a gaseous stream which is rich in helium and a denitrided stream of hydrocarbons and associated installation

Installation for 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 installation comprising:

• means for expanding of the feed stream in order to form an expanded feed stream;
• means for dividing the expanded feed stream into a first introduction stream and a second introduction stream;
• means for cooling the first introduction stream comprising an upstream heat exchanger and a cooling cycle, in order to obtain a first cooled introduction stream by means of heat exchange with a gaseous refrigerant stream which is obtained by dynamic expansion in the cooling cycle;
• means for cooling the second introduction stream comprising a first downstream heat exchanger in order to form a second cooled introduction stream;
• a fractionating column comprising a plurality of theoretical fractionating stages;
• means for introducing the first cooled introduction stream and the second cooled introduction stream into the fractionating column;
• means for tapping at least one reboiling stream and means for circulating the reboiling stream in the first downstream heat exchanger in order to cool the second introduction stream;
• means for tapping, at the bottom of the fractionating column, a bottom stream which is intended to form the denitrided stream of hydrocarbons;
• means for tapping, at the head of the fractionating column, an head stream which is rich in nitrogen;
• means for reheating the nitrogen rich head stream comprising at least a second downstream heat exchanger in order to form a reheated stream which is rich in nitrogen;
• means for tapping and expanding a first portion of the nitrogen rich reheated stream in order to form the gaseous nitrogen stream;
• means for compressing a second portion of the nitrogen rich reheated stream in order to form a recycled nitrogen stream and means for cooling the compressed, recycled nitrogen stream by means of circulation through the first downstream heat exchanger and the or each second downstream heat exchanger;
• means for partially liquefying and expanding the recycled nitrogen stream in order to form an expanded nitrogen rich stream;
• a first separation container;
• means for introducing at least a portion obtained from the expanded nitrogen rich stream into the first separation container;
• means for recovering the gaseous head stream from the first separation container in order to form the helium rich stream;
• means for recovering the liquid stream from the bottom of the first separation container and for separating that stream into a liquid nitrogen stream and a first reflux stream;
• means for introducing the first reflux stream as reflux into the head of the fractionating column.