METHOD FOR OBTAINING PURE NITROGEN FROM NATURAL GAS STREAM CONTAINING NITROGEN Russian patent published in 2023 - IPC F25J1/00 

FIELD: gas industry.

SUBSTANCE: invention relates to a process for liquefying a natural gas stream, comprising the following steps: a) cooling an incoming gas stream to obtain a liquefied natural gas stream at a temperature T1; b) injecting the stream obtained in step a) into a denitration column at a pressure P2 and at a temperature T2 which is lower than T1, producing a denitrated liquefied natural gas stream at the bottom of said column and at the top a nitrogen-enriched vapour stream; c): condensing the nitrogen-enriched vapour stream obtained in step b) in a heat exchanger; d): injecting the stream obtained in step c) into a phase separation vessel to obtain a liquid stream and a gas stream enriched in nitrogen; e): injection of the gas stream obtained in step d) into the distillation column at pressure P2, obtaining at the top a nitrogen-enriched stream containing less than 1% methane and at the bottom a liquid stream containing less than 10% nitrogen. At least one part of the liquid stream obtained in step b) is used in step c) to cool the nitrogen-enriched vapour stream obtained in step b) in said heat exchanger; step f): the portion of the liquid stream obtained in step b) that is not used in step c) is cooled by indirect heat exchange with the second gaseous fraction obtained in step g) to obtain a cooled liquid fraction and a second heated gaseous fraction. The method also includes step g): the cooled liquid fraction obtained in step f) is expanded and then introduced into the second phase separation vessel (B1) to obtain liquefied natural gas and a second gaseous fraction; step h): at least a portion of the second heated gaseous fraction obtained in step g) is compressed to a pressure P1; step i): at least a portion of the liquid stream obtained in step e) is cooled by indirect heat exchange; step j): the stream obtained in step i) is mixed with the expanded mixture obtained in step g) before being introduced into said second phase separation vessel (B1).

EFFECT: reduction in capital costs and energy costs.

12 cl, 1 dwg, 1 tbl