A techno-economic comparison of biological and chemical routes for CO2 methanation in renewable LNG production

Liquefied Natural Gas (LNG) has recently emerged as a promising substitute maritime fuel, due to its potential of reducing GHG emissions with respect to heavy fuel oils. This paper analyses and compares from a techno-economic point of view different technological pathways for renewable LNG production to be used as bunker fuel in North-Eastern Italy. Specifically, CO2 hydrogenation (a process also known as methanation) is considered, either starting from carbon dioxide captured from industrial flue gases (e-LNG), or from the biogas obtained via anaerobic digestion of biomass (bio-LNG). Moreover, both chemical (via the Sabatier reaction) and biological (exploiting hydrogenotrophic microorganisms) methanation have been considered. Results show that the bio-LNG route is more economically feasible with a Levelized Cost of Methane (LCOM) of about 150 €/MWh, but feedstock availability strongly limits the LNG throughput. On the other hand, the e-LNG route can reach larger production capacity, with a LCOM of around 200 €/MWh. Biological methanation is currently slightly less profitable compared to the chemical route mainly due to large investment costs, however technological advancements could significantly improve the economic performances.