Method and system for upgrading biogas using PSA

A method of upgrading biogas comprising methane and nitrogen, the method comprising:

• (i) providing the biogas in at least one pressurized vessel, the biogas provided at least initially at a pressure of at least 65 atm (6586 kPa);
• (ii) treating at least a portion of the biogas in a pressure swing adsorption (PSA) process, the PSA process comprising feeding the portion of the biogas into a first adsorbent bed disposed in series with a second adsorbent bed, the first adsorbent bed having an inlet end and an outlet end, the first adsorbent bed comprising an adsorbent selective for nitrogen over methane and subjected to a first PSA cycle, the first PSA cycle comprising:
• a) a feed phase, wherein the first portion of the biogas is fed into the first adsorbent bed when the inlet end is open and the outlet end is closed, thereby pressurizing the first adsorbent bed to a first pressure and preferentially adsorbing the nitrogen over the methane, the first pressure at least 40 atm (4053 kPa);
• b) a first depressurization phase, wherein the inlet end is closed, the outlet end is open, and a first gas enriched in methane is withdrawn through the outlet end as the pressure of the first adsorbent bed falls to a second pressure, the second pressure at least 34 atm (3447 kPa) and lower than the first pressure, at least a portion of the first gas enriched in methane provided as product gas;
• c) a second depressurization phase, wherein the inlet end is closed, the outlet end is open, and a second gas enriched in methane is withdrawn through the outlet end as the pressure of the first adsorbent bed falls to a third pressure, the third pressure lower than the second pressure, at least a portion of the second gas enriched in methane used within the PSA process;
• d) a third depressurization phase, wherein gas is withdrawn from the inlet end, the outlet end, or a combination thereof, as the pressure of the first adsorbent bed falls to a fourth pressure, the fourth pressure lower than the third pressure, at least a portion of the withdrawn gas recycled for use in the feed phase;
• and
• e) optionally, a regeneration phase, wherein the first adsorbent bed is depressurized to 1 atm (101 kPa) or lower, subjected to a purge step, or a combination thereof.

A method of upgrading biogas comprising methane and nitrogen, the method comprising:

• (i) providing the biogas in at least one pressurized vessel, the biogas provided at least initially at a pressure of at least 65 atm (6586 kPa);
• (ii) treating at least a portion of the biogas in a pressure swing adsorption (PSA) process, the PSA process comprising feeding the portion of the biogas into an adsorbent bed, the adsorbent bed having an inlet end and an outlet end, the adsorbent bed comprising an adsorbent selective for nitrogen over methane and subjected to a PSA cycle, the PSA cycle comprising:
• a feed phase, wherein the portion of the biogas is fed into the adsorbent bed when the inlet end is open and the outlet end is closed, thereby pressurizing the adsorbent bed to a first pressure and preferentially adsorbing the nitrogen over the methane, the first pressure being at least 40 atm (4053 kPa);
• a first depressurization phase, wherein the inlet end is closed, the outlet end is open, and a gas enriched in methane is withdrawn through the outlet end as the pressure of the adsorbent bed falls to a second pressure, the second pressure lower than the first pressure, at least a portion of the gas enriched in methane provided as product gas;
• a methane recovery phase, wherein gas is withdrawn from the inlet end, outlet end, or a combination thereof, as the pressure of the adsorbent bed falls to a third pressure, the third pressure being lower than the second pressure, at least a portion of the gas withdrawn from the adsorbent bed during the methane recovery phase recycled for use in the feed phase, used in a regeneration phase, fed to another bed, or any combination thereof;
• and,
• optionally, the regeneration phase, wherein the adsorbent bed is depressurized to 1 atm (101 kPa) or lower, subjected to a purge step, or a combination thereof.