Process Optimisation of Biogas-Based Power-to-Methane Systems by Simulation

Abstract

Increasing amounts of renewable energy produced by volatile sources like photovoltaic and wind turbines demand for higher energy storage capacities to achieve a sustainable energy generation and supply. Power-to-methane – storing excess energy via chemical conversion as methane – is one of the most interesting technologies to reach this goal, as it bundles the advantages of large storage capacities, fast response time and use of existing infrastructure. First commercial plants have been realised, but alternative concepts are still heavily researched and in demonstration stage. As most are using complex process setups or achieving low methane product concentrations, process optimisation and simplification is needed, but information on this topic is scarce. To close this gap, a power-to-methane process consisting of catalytic methanation and membrane gas upgrading using biogas as carbon dioxide source was simulated in ASPEN Plus®. Four different process setups were modelled to assess influences of fermentation setup, recycling of membrane off-gas and multistage membrane gas separation as well as pressure and GHSV. Models were parameterised with experimental results obtained from a demonstration plant. It was shown that a process without off-gas recycling requires less energy but leads to hydrogen losses of up to 25 %. Preventing this loss by recycling the off-gas leads to an increase of specific energy demand for hydrogen storage by 17 % and relative membrane area by 11 % for the base case.