Direct vs. indirect biogas methanation for liquefied biomethane production: A concept evaluation

Abstract

Conventional liquefied biomethane (LBM) production plants consist of upgrading and liquefaction processes. Commonly, the captured CO2 during biogas upgrading is emitted into the atmosphere. One alternative, to produce more LBM, is to combine the conventional LBM production plant with the Power-to-Gas concept. Within this context, green H2 produced from renewable electricity can react with the CO2 in the biogas mixture, producing additional CH4. The present study evaluated the feasibility of integrating methanation with conventional LBM production plants. The performance of the proposed process designs was assessed through exergy and cost analysis considering detailed models. The results illustrated that integrated direct biogas methanation was superior to methanation of captured CO2. The integrated scheme with direct biogas methanation increased the LBM production by 52.2 % compared to the conventional LBM production plant but with lower exergy efficiency. It was indicated the feasibility of the integrated scheme through direct biogas methanation was highly dependent on the price of H2. A H2 price of 1.27 USD/kg H2 was required to produce LBM at a similar price as the conventional LBM production plant.