Multi-stage PSA process to remove contaminant gases from raw methane streams
A multi-stage process to remove contaminant gases from raw methane streams is provided. The present technology is an innovative solution to recover and purify biogas by use of a process having at least two pressure swing adsorption stages. Taking advantage of the presence of carbon dioxide in the raw biogas streams, nitrogen and oxygen are bulky removed in the first stage, using selective adsorbents, and a nitrogen and oxygen-depleted intermediate stream is yielded to the second stage. The second stage employs an adsorbent or adsorbents to selectively remove carbon dioxide and trace amounts of remaining nitrogen and oxygen, thus producing a purer methane stream that meets pipeline and natural gas specifications.
1. A multi-stage Pressure Swing Adsorption process to remove contaminant gases from raw methane streams, comprising at least two Pressure Swing Adsorption stages:
a first stage for removing Nitrogen and Oxygen, comprising the following steps:
Feed (“FD”);
Adsorption (“AD”);
Equalization provided (“ET”);
Blowdown (“BD”);
Evacuation (“EV”);
Purge (“PG”);
Equalization received (“E↓”),
wherein the first stage comprises at least one adsorbent, or mixture thereof, with strong affinity for carbon dioxide and methane;
second stage for removing Carbon Dioxide and residual Nitrogen and Oxygen comprising the following steps:
Adsorption (“AD”);
Co-current depressurization (“COD”);
First equalization provided (“E 1 ↑”);
Second equalization provided (“E 2 ↑”);
Evacuation (“EV”);
First equalization received (“E 1 ↓”);
Idle (“ID”);
Second equalization received (“E 2 ↓”);
Idle (“ID”);
wherein the second stage comprises at least one adsorbent, or mixture thereof, with strong affinity for carbon dioxide.
2. The process according to claim 1 , wherein the second stage further comprises a Blowdown (“BD”) stage after the Second equalization provided (“E 2 ↑”) step and before the Evacuation (“EV”) step.
3. The process according to claim 2 , wherein the Co-current depressurization (“COD”) step of the second stage occurs after the Second equalization provided (“E 2 ↑”) and before the Evacuation (“EV”) step.
4. The process according to claim 1 , wherein the second stage comprises a Backfill (“BF”) stage after the Second equalization received (“E 2 ↓”) and before the second Idle (“ID”) stage.
5. The process according to claim 1 , wherein the second stage comprises a Backfill (“BF”) stage after the second Idle (“ID”) stage.
6. The process according to claim 1 , wherein it comprises a pre-treatment step before the first stage.
7. The process according to claim 1 , wherein the first stage operates at a temperature between −50° C. and 120° C.
8. The process according to claim 1 , wherein the operating pressure during the adsorption step in the first stage is between 60 kPa and 1500 kPa.
9. The process according to claim 8 , wherein the purge to feed ratio varies between 0.3 to 0.9 depending on nitrogen feed stream content.
10. The process according to claim 1 , wherein the operating desorption pressure in the evacuation step of the first stage ranges from 1 kPa to 100 kPa.
11. The process according to claim 1 , wherein an intermediate biogas stream resultant of the first stage is pressurized between 200 kPa to 4,000 kPa and fed to the adsorption beds of the second stage.
12. The process according to claim 1 , wherein the second stage operates at a temperature between −50° C. to 150° C.
13. The process according to claim 1 , wherein the operating pressure during the adsorption step of the second stage is between 200 kPa and 4,000 kPa.
14. The process according to claim 1 , wherein the operating desorption pressure in the evacuation step of the second stage is between 0.001 kPa and 100 kPa.
15. The process according to claim 1 , wherein adsorbents used in the first and second stage are selected from the group consisting of zeolites, titanosilicates, metal-organic frameworks, activated carbons, carbon molecular sieves, alumina, silica gel, ionic liquid zeolites and Si/Al-based mesoporous materials.
16. The process according to claim 1 , wherein the first stage equalization occurs through the top of adsorbent vessels.
17. The process according to claim 1 , wherein the first stage equalization occurs through the bottom of adsorbent vessels.
18. The process according to claim 1 , wherein the desorption in the evacuation step of the second stage occurs with purge.
19. The process according to claim 1 , wherein the desorption in the evacuation step of the second stage occurs without purge.