Direct catalytic methanation of biogas – Part II: Techno-economic process assessment and feasibility reflections.

Highlights • Detailed costs analysis of Power-to-Gas processes with biogas conducted. • Main cost impact caused by electrolysis, biogas costs and electricity consumption. • Fixed bed reactors are two time more expensive than fluidised bed reactors. • Power-to-Gas processes can be profitable until electricity prices of 5.3–6.0 Ct € /kWh el. • The most feasible process contains a fluidised bed methanation and a membrane with 22.7 Ct € /kWh new production costs. Abstract Six different processes for the direct methanation of biogas for biomethane production were evaluated regarding their economically optimised operating conditions, their absolute costs and profitability. Detailed process simulations turned out to be important to obtain a solid process design so that a realistic cost estimate is possible. This is necessary since the stated costs in literature vary by a factor of 10 due to the shortage of simulation details. In addition, cost data for the methanation from recent literature are often under-estimated due to the lack of a required second upgrading step (post-upgrading) to reach the demanded gas grid specifications and of additional process equipment. A fixed bed methanation reactor is two times more expensive than a bubbling fluidised bed reactor but due to the dominant share of costs of the electrolysis, costs differences between the whole processes of 5% are less pronounced. It turned out that a gas separation membrane and a second fixed bed, as a post-upgrading step, are equally expensive. However, a gas separation membrane seems to be technically more robust. Biomethane production costs of 10.2 Ct € /kWh total for processes containing a fluidised bed and of 10.7 Ct € /kWh total for processes containing a main fixed bed are obtained. As a consequence, the corresponding processes are profitable until an electricity price of 6.0 Ct € /kWh el and 5.3 Ct € /kWh el without considering the extra revenues from process heat and oxygen. Furthermore, the profitability of the processes increases with the methane content in the biogas. Considering extra revenues and a concentration increase of 10% for methane in the biogas, the maximum electricity price for a profitable process increases by 3 Ct € /kWh el. [ABSTRACT FROM AUTHOR]