Techno-Economic Modeling of a Liquid Scrubbing Process for the Co-Production of Biomethane and Biomethanol from Syngas

In this study, an Aspen Plus model was developed to compare the techno-economic performance of two processes comprising integrated biomass gasification, low-pressure water and methanol syngas scrubbing, electrolysis and syngas biomethanation. The first process operates standalone biomethanation (SAB) of syngas and can produce approximately 38,000 Nm3/day of bio-synthetic natural gas (bSNG). The second process (integrated biomethanebiomethanol, IBB) exploits the unconverted carbon stream from the biomethanation process to co-produce biomethanol via direct catalytic CO2 hydrogenation. In addition to the same bSNG output of SAB, the IBB process can produce 10 t/day of biomethanol. Liquid scrubbing delivers a 64% reduction in specific work input before electrolysis, compared to conventional syngas conditioning, but it increases the demand for additional hydrogen. Although IBB shows limited energy efficiency gains due to the large increase in electrolytic hydrogen demand, it shows a substantial improvement (+27%) in biomass-to-fuel carbon efficiency. The SAB and IBB processes generate a bSNG minimum selling price of 2.38 €/Nm3 and 3.68 €/Nm3, respectively. High electrolysis costs primarily cause the bSNG market price gap to remain substantial, namely in the range of 0.19 – 0.27 €/kWh. Intensive fiscal support is required to sustain the co-production of biomethane and biomethanol under the proposed process scheme.