Thermodynamic and environmental study on synthetic natural gas production in power to gas approaches involving biomass gasification and anaerobic digestion

The main goal of this paper is to assess and compare three hybrid systems for the production of synthetic natural gas (biomethane) from biogas or process gas. Mathematical models were built to determine the main performance indicators and plant efficiency of the proposed solutions, such as mass and energy flows and gas composition in characteristic points of the systems, as well as the efficiencies of the full chains. The carbon footprint of the three approaches was calculated using a streamlined life cycle assessment. The results show that both methanation cases may be an interesting option for SNG production and energy storage. The energy efficiency of the solutions reaches a value of 84% for Case 1 (methanation from syngas) and 90% for Case 2 (methanation of biogas) and 3 (biogas upgrading), respectively. If the manure credit is accounted for emissions, the carbon footprint of biomethane from Case 3 is the lowest.