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AirScience CO2 Removal System
AirScience Technologies offers several processes to separate and remove carbon dioxide (CO2) from
biogas and natural gas.
To produce biogas for use in an internal combustion engine and power generation, operators usually do not remove carbon dioxide from the biogas, however for injection into the city gas network, the biogas needs to meet stringent specifications and carbon dioxide has to be removed. In the case where the gas will be liquefied, carbon dioxide has to be removed to ppm level.
The most commonly used for biogas applications are vacuum pressure swing adsorption (VPSA) or multistage membrane system. In cases where ppm levels of carbon dioxide are required, amine scrubbing process is used.
Vacuum Pressure Swing Adsorption (VPSA) Process
In VPSA process, biogas is passed through a bed made of specific adsorbent, typically, methane goes through the bed and all other impurities including carbon dioxide are adsorbed by the media.
To achieve high methane quality, the media in the tower has to be desorbed after a short period of time. The adsorption occurs under pressure to allow high performance and compact equipment size.
In order to recover as much of the pressure as possible as well as to minimize the loss of valuable methane, a number of towers are installed in parallel and operating in a cascading fashion where a tower under desorption mode will vent into a tower at a lower pressure and so on until vacuum of the last tower and re-pressurization, then adsorption mode again.
AirScience, VPSA operating sequence has been optimized to provide for one of the highest methane recovery of this technology worldwide.
Vacuum Swing Adsorption (VSA) Process
This process which is used at low gas pressure, as opposed to VPSA which is used under pressure, is a good and low cost alternative to other processes for the dehumidification of biogas and the enrichment of methane in biogas.
In VSA process, biogas is passed through a bed made of specific adsorbent, typically, methane goes through the bed and all other impurities including carbon dioxide are adsorbed by the media. To achieve high methane quality, the media in the tower has to be desorbed after a short period of time. The adsorption occurs at low pressure and the desorption is performed by applying vacuum to the vessel being regenerated.
As VSA applies much less energy to the desorption process than VPSA, this process is not suited for all applications as some contaminants might not be desorbed from the media under the sole vacuum applied.
Amine Scrubbing Process
Amine scrubbing or amine gas treating, also known as gas sweetening or acid gas removal, refers to a group of processes that use aqueous solutions of various alkylamines to remove hydrogen sulfide (H2S) and carbon dioxide (CO2) from gases.
AirScience amine scrubbing process includes absorber and regenerator towers as well as accessory equipment such as pumps, heat exchangers, reboiler, etc.
In the absorber, the down-flowing amine solution absorbs H2S and CO2 from the up-flowing sour gas to produce a sweetened gas stream (i.e., a gas free of hydrogen sulfide and carbon dioxide) as a product exiting at the top of the tower and an amine solution rich in the absorbed acid gases collecting at the bottom of the tower.
The resultant "rich" amine is then routed into the regenerator (a stripper with a reboiler) to produce regenerated or "lean" amine that is recycled for reuse in the absorber.
The stripped overhead gas from the regenerator is concentrated H2S and CO2. In the case of biogas enrichment that stripped gas is mostly carbon dioxide.