Process for purifying natural gas and liquefying carbon dioxide

Patent metadata

Field	Value
Publication number	US-10415879-B2
Application number	US-201715611356-A
Country	US
Kind code	B2
Filing date	Jun 1, 2017
Priority date	Jun 2, 2016
Publication date	Sep 17, 2019
Grant date	Sep 17, 2019

Abstract

A process for producing liquefied natural gas and liquid carbon dioxide from a natural gas feed gas comprising at least the following steps: Separation of a natural gas feed gas into a CO 2 -enriched gas stream and a natural gas stream; Cooling of said natural gas in a heat exchanger; Purification of the in step 1 from compounds containing at least six carbon atoms; At least partial condensation of said gas stream resulting from step 3 to form a two-phase stream; Separation of said two-phase stream resulting from step 4 to form a gas stream and a liquid stream; Condensation of the gas stream resulting from step 5 to form a liquefied gas containing less than 5 ppm by volume of compounds containing at least six carbon atoms; Liquefaction of the CO 2 -enriched gas stream resulting from step 1 with a portion of the liquid stream resulting from step 5.

First claim

What is claimed is:

1. A process for producing liquefied natural gas and liquid carbon dioxide (CO 2 ) from a natural gas feed gas further comprising carbon dioxide and at least 10 ppm by mole of hydrocarbons having at least six carbon atoms, the process comprising at least the following steps:
Step a): separating the natural gas feed gas in a treatment unit, into a CO 2 -enriched gas stream and a natural gas stream;
Step b): cooling said natural gas stream to a temperature between −20° C. and −60° C. by heat exchange with at least one refrigerant in a first heat exchanger;
Step c): purifying the natural gas stream from hydrocarbons having at least six carbon atoms in a scrubbing column, wherein at a top portion of the scrubbing column, a top gas stream containing less than 5 ppm by volume of hydrocarbons having at least six carbon atoms is withdrawn, and, at a bottom portion of the scrubbing column, a bottom liquid stream enriched in hydrocarbons having at least five carbon atoms is withdrawn;
Step d): at least partially condensing said top gas stream resulting from step c) in a second heat exchanger in order to form an at least partially condensed top gas stream;
Step e): separating said at least partially condensed top gas stream resulting from step d) in a phase separator vessel at a temperature between −60° C. and −80° C. in order to form a gas stream at the top of the vessel and a liquid stream at the bottom of the vessel;
Step f): introducing a first portion of the liquid stream resulting from step e) at the top portion of the scrubbing column in order to effect reflux at the top portion of the scrubbing column;
Step g): condensing the gas stream resulting from step e) by heat exchange in a third heat exchanger at a temperature below −100° C. in order to form a liquefied gas containing less than 5 ppm by volume of hydrocarbons having at least six carbon atoms;
Step h): liquefying the CO 2 -enriched gas stream resulting from step a) by heat exchange with a second portion of the liquid stream resulting from step e).

2. The process of claim 1 , wherein the feed gas comprises from 0.1 mol % to 5 mol % of CO 2 .

3. The process of claim 1 , wherein the top gas stream resulting from step c) and the liquefied natural gas resulting from step d) contain less than 1 ppm by mole of hydrocarbons having at least six carbon atoms.

4. The process of claim 1 , wherein the CO 2 -enriched gas stream resulting from step a) comprises at least 95 mol % of CO 2 .

5. The process of claim 1 , wherein said treatment unit used in step a) is an amine scrubbing unit.

6. The process of claim 1 , wherein said hydrocarbons having at least six carbon atoms comprise a majority of benzene.

7. The process of claim 1 , wherein the natural gas stream is cooled in step b) to a temperature that is between −20° C. and −40° C.

8. The process of claim 1 , wherein the second portion of the liquid stream resulting from step e), having been used to liquefy the CO 2 -enriched stream during step g), is then reinjected into the bottom of the scrubbing column.

9. The process of claim 1 , wherein the second heat exchanger is separate from the first heat exchanger or is a second section of the first heat exchanger.

10. The process of claim 1 , wherein the third heat exchanger is separate from the first heat exchanger or is a third section of the first heat exchanger.

Assignees

• Air Liquide

Inventors

• Costa De Beauregard Pierre
• Murino Michele
• Pichot Delphine

Classifications

• F25J2290/12

  Particular process parameters like pressure, temperature, ratios · CPC title

• F25J2270/66

  Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons · CPC title

• F25J2270/18

  External refrigeration with incorporated cascade loop · CPC title

• F25J2260/20

  Integration in an installation for liquefying or solidifying a fluid stream · CPC title

• F25J2245/02

  Recycle of a stream in general, e.g. a by-pass stream · CPC title