Process for the removal of CO2 from acid gas

Patent metadata

Field	Value
Publication number	US-9945605-B2
Application number	US-201314432726-A
Country	US
Kind code	B2
Filing date	Oct 1, 2013
Priority date	Oct 1, 2012
Publication date	Apr 17, 2018
Grant date	Apr 17, 2018

Abstract

The invention relates to a process for the removal of CO 2 from acid gas by cryogenic distillation performed in two steps. The feed mixture is first distilled at high pressure (at least 45 bar) in a first distillation column. The top product or a part thereof is then, after heating, subjected to a second distillation step at a lower pressure (lower than 45 bar). The top product of the second distillation step is methane of high purity (more than 99 mol. %). The bottom product of the second distillation step is recycled back to the first distillation column. The method according to the invention allows complete separation of methane also at higher level of acidic components, is economical and does not result in solid CO 2 build-up, which is a common problem in cryogenic distillation.

First claim

The invention claimed is:

1. A method for the removal of carbon dioxide (CO 2 ) from a feed mixture comprising methane and carbon dioxide (CO 2 ), the method comprising a first distillation step and a second distillation step:
(a) subjecting the feed mixture to the first distillation step in a first distillation column or a first section of a distillation column, at a first distillation pressure of at least 45 bar, yielding after said first distillation a first bottom product stream comprising CO 2 and a first top product stream comprising CO 2 and methane,
(b) splitting said first top product stream into a first part and a second part, heating the first part of said first top product stream to yield a first heated part of said first top product stream, cooling the second part of said first top product stream by heat exchange with a heat exchange medium to yield a second cooled part of said first top product stream, followed by
(c) reducing the pressure of said first heated part of the first top product stream to provide a second distillation feed stream, and thereafter subjecting said second distillation feed stream to the second distillation step in a second distillation column or a second section of the distillation column, at a second distillation pressure, wherein said second distillation pressure is lower than 45 bar, yielding thereby a second top product stream comprising methane and a second bottom product stream,
(d) feeding said second bottom product stream to said first distillation column or said first section of the distillation column,
(e) feeding said second cooled part of said first top product stream to said second distillation column or a second section of the distillation column,
wherein said second distillation feed stream has a dew point temperature at said second distillation pressure,
wherein said heating in step (b) results in a temperature of said second distillation feed stream higher than said dew point temperature of said second distillation feed stream at said second distillation pressure,
and wherein said reducing of pressure of step (c) is carried out while the temperature of the said first heated part of the first top product stream is higher than said dew point temperature of said second distillation feed stream at said second distillation pressure.

2. The method according to claim 1 , wherein the first heated part in (b) is at least 10 mol. % of the first top product stream.

3. The method according to claim 1 , wherein the said part that is not heated in step (b) is fed to the second distillation column or the second section of the distillation column as a liquid phase.

4. The method according to claim 1 , wherein the feed mixture enters the first distillation step at a feed mixture entry pressure and a feed mixture temperature, wherein the feed mixture has a feed mixture dew point temperature at said feed mixture entry pressure, and wherein said feed mixture temperature is equal to or lower than said feed mixture dew point temperature.

5. The method according to claim 1 , wherein the first distillation pressure is in the range of 45-55 bar.

6. The method according to claim 1 , wherein the second distillation pressure is higher than 35 bar.

7. The method according to claim 1 , wherein in step (b) the first heated part of the first top product stream is heated to a temperature that is between 1 and 10° C. higher than the dew point of the first part of the first top product stream at the second distillation pressure.

8. The method according to claim 1 , wherein the first distillation pressure and second distillation pressure differ by at least 2 bar.

9. The method according to claim 1 , wherein the second top product stream comprises at least 98 mol. % methane.

10. The method according to claim 1 , wherein the second top product stream is partially condensed in a partial condenser.

11. The method according to claim 1 , wherein the first bottom product stream is reboiled in a reboiler before entering the first distillation column or the first section of the distillation column.

12. The method according to claim 1 , wherein the distillation steps are performed in a distillation column, wherein said distillation column is a dual-pressure distillation column having internals with a tray or packing design.

13. The method according to claim 1 , wherein the reducing of pressure in step (c) is by means of a valve and wherein the temperature at the outlet of the valve is between 3 and 8° C. higher than said dew point of the second distillation feed stream.

Assignees

• Stamicarbon
• Pellegrini Laura Annamaria
• Tecnimont Spa

Inventors

• Pellegrini Laura Annamaria

Classifications

• F25J2200/74

  Refluxing the column with at least a part of the partially condensed overhead gas · CPC title

• F25J2200/08

  in a triple pressure main column system · CPC title

• F25J2200/78

  Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column · CPC title

• Y02C10/12

  Cross-Sectional Technologies · mapped topic

• F25J3/0233

  separation of CnHm with 1 carbon atom or more · CPC title