Low-cost dual-stage vacuum swing adsorption (VSA) for simultaneous biomethane and biogenic CO2 production from biogas

Biogas is often produced at ambient pressure and compressed to 4–8 bar before upgrading, increasing energy consumption and requiring an expensive feed compressor. We have evaluated two different configurations of two-stage Vacuum Swing Adsorption system with ambient adsorption pressure (flow driven by a blower) for simultaneous production of bio-methane and biogenic CO 2 . Configuration 1 has a front stripping section where high-purity CO 2 is removed, followed by a rectifying section where bio-methane is obtained. In Configuration 2, bio-methane is produced in a frontal rectification section, and its bottom product (a low-purity CO 2 stream) is routed to a back stripping section. Configuration 2 achieved superior CO 2 purity (>99.5 mol%) and lower energy requirement 540 kJ/kg biomethane . The effect of adsorbent performance was also evaluated by replacing carbon molecular sieve (CMS) by cheaper silica gel in the stripping section. The best configuration produced biomethane at 0.575 USD/Nm 3 , rising to 0.757 USD/Nm 3 when compressed to 200 bar as vehicular biofuel. The estimated payback period for this system is approximately 7.3 years. However, valorization of the captured CO 2 through carbon credits marginally reduces the payback period to about 7 years.