Method for denitrogenation of natural gas with or without helium recovery

Patent metadata

Field	Value
Publication number	US-10006699-B2
Application number	US-201415029107-A
Country	US
Kind code	B2
Filing date	Oct 14, 2014
Priority date	Oct 18, 2013
Publication date	Jun 26, 2018
Grant date	Jun 26, 2018

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

The invention claimed is:

1. 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, wherein the system of columns 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;
ii) withdrawing a nitrogen-enriched gas from the second column and then heating said nitrogen-enriched gas in the exchange line;
iii) withdrawing a methane-enriched liquid from the second column, and then pressurizing the methane-enriched liquid to form a pressurized methane-rich liquid;
iv) splitting the pressurized methane-rich into at least a first fraction and a second fraction, wherein the first fraction is at a first fraction pressure (P 1 );
v) expanding the second fraction to a second expanded pressure (P 2 ), wherein the P 2 is less than the P 1 ;
vi) vaporizing the first fraction and the second fraction within the exchange line to form a gaseous first fraction and a gaseous second fraction, wherein the first fraction vaporizes at the P 1 and the second fraction vaporizes at the P 2 ; and
vii) using a nitrogen-enriched gas from the top portion of the first column as a reboiling fluid for the vaporizer-condenser;
wherein at least part of the cooled natural gas expands in gaseous form in a turbine and is sent to the first column in gaseous form,
wherein energy supplied by the turbine is harnessed in at least one compressor which compresses a process gas, wherein the process gas is selected from the group consisting of the nitrogen-enriched gas from the top portion of the first column, the gaseous second fraction withdrawn from an intermediate location of the exchange line, and combinations thereof wherein the process gas is the gaseous second fraction withdrawn from an intermediate location of the exchange line and in order to be compressed in the at least one compressor and is then sent back to the exchange line for further warming therein.

2. The method as claimed in claim 1 , the at least part of the cooled natural gas is a first part of the cooled natural gas and the cooled natural gas further comprises a second part of the cooled natural gas which condenses at least partially and is sent in at least partially condensed form to first column.

3. The method as claimed in claim 1 , wherein the at least one compressor which compresses the process gas has an inlet temperature lower than −150° C.

4. The method as claimed in claim 3 , wherein the at least one compressor is directly driven by the turbine.

5. The method as claimed in claim 1 , wherein an intermediate liquid withdrawn from the first column is expanded and sent to the second column at an intermediate level or at the top level.

6. The method as claimed in claim 1 , wherein the at least part of the natural gas cooled in the exchange line and sent to the turbine remains gaseous as the at least part of the natural gas cooled in the exchange line cools upstream of the turbine.

7. The method as claimed in claim 1 , wherein the at least part of the cooled natural gas intended for the turbine is withdrawn at an intermediate level of the exchange line.

8. The method as claimed in claim 2 , wherein the second part of the natural gas cools as far as the cold and of the exchange line.

9. A method for denitrogenation of a natural gas stream, the method comprising the steps of:
providing an insulated cold box having a system of columns and an exchange line disposed within, wherein the system of columns comprises a higher pressure column and a lower pressure column, wherein the higher pressure column operates at a high pressure between 10 and 30 bara, wherein the lower pressure column operates at a low pressure between 0.8 and 3 bara, wherein the lower pressure column and the higher pressure column are thermally connected via a vaporizer-condenser,
introducing the natural gas stream into the insulated cold box at a pressure above the high pressure and cooling the natural gas stream within the exchange line;
expanding a first portion of the cooled natural gas stream in a turbine and then sending the expanded first portion of the natural gas stream to the higher pressure column for separation therein;
condensing a second portion of the natural gas stream in the exchange line and then expanding the condensed second portion of the natural gas stream in an expansion valve before being sent in liquid form to the higher pressure column for separation therein;
producing a methane-enriched liquid at a bottom portion of the higher pressure column and a nitrogen-enriched gas at a top portion of the higher pressure column;
using the nitrogen-enriched gas from the top portion of the higher pressure column as a reboiling fluid for the vaporizer-condenser,
withdrawing the methane-enriched liquid from the higher pressure column and introducing the methane-enriched liquid to the lower pressure column after expansion in a second expansion valve;
producing a methane-rich liquid at a bottom portion of the lower pressure column and a residual nitrogen gas at a top portion of the lower pressure column;
withdrawing the methane-rich liquid from the lower pressure column and increasing the pressure of the methane-rich liquid using a pump to form a pressurized methane-rich liquid;
splitting the pressurized methane-rich liquid into at least a first fraction and a second fraction, wherein the first fraction is at a first fraction pressure (P 1 );
expanding the second fraction in a third expansion valve to a second expanded pressure (P 2 ), wherein the P 2 is less than the P 1 ; and
vaporizing the first fraction and the second fraction within the exchange line to form a gaseous first fraction and a gaseous second fraction, wherein the first fraction vaporizes at the P 1 and the second fraction vaporizes at the P 2 ,
wherein energy supplied by the turbine is harnessed in a cold compressor which compresses a process gas at a temperature below that of a warm end of the exchange line, wherein the process gas is selected from the group consisting of the nitrogen-enriched gas from the top portion of the first column, the gaseous second fraction after being withdrawn from an intermediate location of the exchange line, and combinations thereof further comprising the step of withdrawing the gaseous second fraction from an intermediate location of the exchange line and compressing the gaseous second fraction in a cold booster to form a boosted second fraction, and then reintroducing the boosted second fraction into the exchange line for further warming within the exchange line.

10. The method as claimed in claim 9 , wherein the step of splitting the pressurized methane-rich liquid further includes a third fraction, wherein the method further includes the steps of:
expanding the third fraction in a fourth expansion valve to a third expanded pressure (P 3 ), wherein the P 3 is less than the P 1 , wherein the P 3 is different than the P 2 ; and
vaporizing the third fraction within the exchange line, wherein the third fraction vaporizes at the P 3 .

11. The method as claimed in claim 9 , wherein the step of using the nitrogen-enriched gas from the top portion of the higher pressure column as a reboiling fluid for the vaporizer-condenser further comprises t

Assignees

• Air Liquide
• Air Liquide

Inventors

• Briglia Alain
• Chouik Selim

Classifications

• F25J2240/02

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

• F25J3/02 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

• F25J2235/60

  the fluid being (a mixture of) hydrocarbons · CPC title

• F25J2230/60

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

• F25J2200/06

  in a classical double column flow-sheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column · CPC title