Method for denitrogenation of natural gas with or without helium recovery

Patent metadata

Field	Value
Publication number	US-2016245584-A1
Application number	US-201415029107-A
Country	US
Kind code	A1
Filing date	Oct 14, 2014
Priority date	Oct 18, 2013
Publication date	Aug 25, 2016
Grant date	—

Abstract

The invention relates to a method for denitrogenation of natural gas by distillation, in which natural gas cooled in an exchange line is separated in a system of columns including at least one column, a nitrogen-enriched gas is drawn from one column of the system of columns and is heated in the exchange line, a methane-enriched liquid is drawn from one column of the system of columns, pressurized and vaporized in the exchange line at at least one vaporization pressure, and at least one portion of the cooled natural gas expands in gaseous form in a turbine and is sent to one column of the system of columns in gaseous form.

First claim

1 - 15 . (canceled)

16 . A method for the removal of nitrogen from natural gas by distillation, the method comprising the steps of:
i) cooling natural gas in an exchange line and then separating said cooled natural gas in a system of columns comprising at least one column; ii) withdrawing a nitrogen-enriched gas from one column of the system of columns and then heating said nitrogen-enriched gas in the exchange line; and iii) withdrawing a methane-enriched liquid from one column of the system of columns, pressurizing the methane-enriched liquid and then vaporizing the pressurized methane-enriched liquid in the exchange line to at least an evaporating pressure, wherein at least part of the cooled natural gas expands in gaseous form in a turbine and is sent to one of the columns of the system of columns in gaseous form, wherein the methane-enriched liquid is vaporized in the exchange line at at least two evaporating pressures.

17 . The method as claimed in claim 16 , wherein a second part of the natural gas condenses at least partially and is sent in at least partially condensed form to one column of the system of columns.

18 . The method as claimed in claim 16 , wherein the methane-enriched liquid withdrawn from one column of the system is fully or partially pumped at one or more pressure level(s) before being vaporized in the exchange line.

19 . The method as claimed in claim 16 , wherein the previously pumped methane-enriched liquid is split into at least two fractions of which at least one is expanded in a valve before vaporizing in the exchange line.

20 . The method as claimed in claim 16 , wherein the energy supplied by the turbine is harnessed in at least one compressor which compresses a process gas, the compressor having an inlet temperature lower than the ambient temperature, or even lower than −150° C.

21 . The method as claimed in claim 20 , wherein the compressor is directly driven by the turbine.

22 . The method as claimed in claim 20 , wherein the process gas is natural gas intended to be separated, a gas produced by distillation, for example the nitrogen-enriched gas or a gas used to transfer heat from one column of the system to another.

23 . The method as claimed in claim 22 , wherein the process gas is produced by vaporizing the methane-enriched liquid in the exchange line.

24 . The method as claimed in claim 22 , wherein the process gas is withdrawn from the exchange line in order to be compressed in the compressor and is then possibly sent back to the exchange line.

25 . The method as claimed in claim 22 , wherein the process gas is a nitrogen-enriched gas coming from one column of the system of columns and which is compressed in the compressor and then used to heat the bottom of another column of the system.

26 . The method as claimed in claim 16 , wherein the system comprises a first column operating at a first pressure, a second column operating at a second pressure lower than the first pressure, the second column being thermally connected to the first column, the natural gas being sent to the first column to produce a bottom liquid and a head gas, at least part of the enriched bottom liquid is sent to the second column, at least part of the head gas being used to heat the bottom of the second column, the nitrogen-enriched gas is withdrawn from the top of the second column and the methane-enriched liquid is withdrawn from the bottom of the second column and the gas expanded in the turbine is sent to the first column in gaseous form.

27 . The method as claimed in claim 26 , wherein an intermediate liquid for the first column is expanded and sent to the second column at an intermediate level or at the top level.

28 . The method as claimed in claim 16 , wherein the at least one part of the natural gas cooled in the heat exchanger and sent to the turbine remains gaseous as it cools upstream of the turbine.

29 . The method as claimed in claim 16 , wherein the part of the natural gas intended for the turbine is withdrawn at an intermediate level of the heat exchanger.

30 . The method as claimed in claim 16 , wherein the second part of the natural gas cools as far as the cold end of the heat exchanger.

Assignees

• Air Liquide
• L'Air Liquide Soc Anonyme Pour I'Etude Et I'Exploitation Des Procedes Georges Claude

Inventors

• Briglia Alain
• Chouik Selim

Classifications

• F25J2230/08

  Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler · CPC title

• F25J3/02 Primary

  by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream (F25J3/08 takes precedence {; purification of hydrocarbons in general C07C7/00}) · CPC title

• F25J2230/60

  the fluid being hydrocarbons or a mixture of hydrocarbons · CPC title

• F25J2240/02

  Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream · CPC title

• F25J3/0257

  separation of nitrogen (from air F25J3/04, production of nitrogen in general C01B21/00) · CPC title