Experimental investigation and energy considerations on hydrate-based biogas upgrading with CO2 valorization

The present paper aims at investigating an innovative biogas upgrading process, based on gas hydrate technology, and at combining it with power-to-gas technology to produce additional synthetic methane. Fuel from the biogas enrichment and the CO2 methanation is characterized by a low life-cycle carbon emission value. In order to assess the viability of the proposed process, the authors carried out both experimental investigations and energy evaluations. Experimental results of the hydrate-based biogas upgrading process, carried out with an up-scaled apparatus, showed that, at 4.5MPa, a methane enrichment of 14.5% was obtained in 60 min, reaching a volume fraction of 70.1%. The separated CO2 was sent to methanation section and converted in methane, with a final volume fraction of 97.24%. Energy evaluations, carried out comparing three different scenarios (utilization of the raw biogas, utilization of the upgraded biogas, utilization of the upgraded biogas and the methane obtained through the methanation of the separated CO2) and considering the energy costs of the three processes, demonstrate that the energy content increase is equal to 22.1% in case of hydrate-based upgrading and 42.0% in case of the integration of the upgrading process and the CO2 methanation. If the electrolysis is considered as an energy cost of the integrated process with CO2 methanation, the energy benefit is just 0.1%. Nevertheless, if hydrogen is produced from renewables, balancing, security and matching issues in the energy systems as well as the CO2 emissions mitigation needs are addressed.