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

An installation configured to produce a liquid nitrogen stream, a gaseous nitrogen stream, a gaseous stream which is rich in helium and a denitrided stream of hydrocarbons, the installation comprising:

• an expansion unit configured to form an expanded feed stream by expanding a feed stream containing hydrocarbons, nitrogen a helium;
• a dividing unit configured to divide the expanded feed stream into a first introduction stream and a second introduction stream;
• a first introduction stream cooling unit configured to cool the first introduction stream, the first introduction stream cooling unit comprising an upstream heat exchanger and a cooling cycle, in order to obtain a first cooled introduction stream by heat exchange with a gaseous refrigerant stream which is obtained by dynamic expansion in the cooling cycle;
• a second introduction stream cooling unit configured to cool the second introduction stream, the second introduction stream cooling unit 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;
• a cooled stream introducer configured to introduce the first cooled introduction stream and the second cooled introduction stream into the fractionating column;
• a reboiling stream tapper configured to tap at least one reboiling stream and a circulator configured to circulate the reboiling stream in the first downstream heat exchanger in order to cool the second introduction stream;
• a bottom tapper positioned at the bottom of the fractionating column and configured to tap a bottom stream to form the denitrided stream of hydrocarbons;
• a head tapper positioned at the head of the fractionating column and configured to tap a head stream which is rich in nitrogen;
• a reheating unit configured to reheat the nitrogen rich head stream and comprising at least a second downstream heat exchanger in order to form a reheated stream which is rich in nitrogen;
• a tapper and expander configured to tap and to expand a first portion of the nitrogen rich reheated stream in order to form the gaseous nitrogen stream;
• a compressor configured to compress a second portion of the nitrogen rich reheated stream in order to form a recycled nitrogen stream and a cooling unit configured to cool the compressed, recycled nitrogen stream by circulation through the first downstream heat exchanger and/or each second downstream heat exchanger;
• a liquefier and expander configured to partially liquify and expand the recycled nitrogen stream in order to form an expanded nitrogen rich stream;
• a first separation container;
• a first separation container introducer configured to introduce at least a portion obtained from the expanded nitrogen rich stream into the first separation container;
• a gas recovery unit configured to recover the gaseous head stream from the first separation container in order to form the helium rich stream;
• a liquid recovery unit configured to recover the liquid stream from the bottom of the first separation container and to separate the recovered liquid stream into a liquid nitrogen stream and a first reflux stream;
• a reflux stream introducer configured to introduce, as reflux, the first reflux stream into the head of the fractionating column;
• a second separation container positioned upstream of the first separation container and upstream of the second downstream heat exchanger;
• an expansion unit configured to expand nitrogen rich stream into the second separation container upstream of the second downstream heat exchanger;
• a head stream introducer configured to introduce the head stream from the second separation container successively into the second downstream 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
• a reflux introducer configured to introduce, as reflux, at least a portion of the bottom stream of the second separation container into the head of the fractionating column.

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:

• expanding the feed stream so as 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 so as to obtain a first cooled introduction stream;
• cooling the second introduction stream by a first downstream heat exchanger so as to form a second cooled 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 so as 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 so as 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 so as 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 so as 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,
• wherein the second introduction stream is introduced in the first downstream heat exchanger without passing through the upstream heat exchanger.

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 into a second separation container positioned upstream of the first separation container;
• introducing the head stream from the second separation container 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;
• introducing, as reflux, at least a portion of the bottom stream of the second separation container into the head of the fractionating column;
• separating the bottom stream of the second separation container into a second reflux stream that is introduced into the fractionating column and a supplementary cooling stream;
• mixing the supplementary cooling stream with the nitrogen rich head stream;
• and
• thereafter introducing the supplementary cooling stream and the nitrogen rich head stream mixture into the second downstream heat exchanger.