Techno-economic assessment of an integrated biomass gasification, electrolysis, and syngas biomethanation process

Biological methanation (biomethanation) of biomass-derived syngas can be a promising alternative to catalytic methanation, due to its milder operating conditions, and could improve the feasibility of power-to-gas and syngas upgrading systems. However, the feasibility of integrating syngas biomethanation with other processes, i.e., electrolysis and gasification, has not been thoroughly assessed so far by the existing literature. In this study, we carried out the techno-economic analysis of such integrated system and we compared it with the production of pure hydrogen. The results indicate that the two processes could produce 0.39 Nm3 of bio-derived substitute natural gas (bSNG) or 0.07 kg of bio-hydrogen (bH2) per kg of dry biomass, respectively. The process cold gas efficiency associated with the produced bSNG is estimated at 50.6%, with a 97.4% input hydrogen utilization efficiency. For bH2, the cold gas efficiency is 36.6%, with 85% hydrogen utilization. Gasification and gas compression were identified as the unit operations with the highest energy demand in both processes. The minimum selling prices (MSP) of the two products were estimated at 2.68 €/Nm3 for bSNG and 15.35 €/kg for bH2. While delivery costs and a limited production capacity pose additional challenges to the development of bH2 production on decentralized gasification plants, bSNG production for grid injection could become a more feasible alternative under appropriate incentive schemes. Key optimization opportunities for such process rely on better heat integration, lower pressure operation, and the use of waste biomass as feedstock.