Implementation of electrofuel production at a biogas plant - Case study at Borås Energi & Miljö

Abstract

One way to decrease the emissions of greenhouse gases is to use a renewable vehicle fuel, such as biogas. By separating methane from carbon dioxide in raw gas in a gas upgrading system, biogas is produced. This study focuses on how to increase the production of biogas by implementing a Sabatier reactor at a biogas plant. The implementation was simulated in Aspen Plus. The simulation was later used together with Aspen Process Economic Analyzer to evaluate the economic performance of the proposed process, including also sensitivity analysis of market changes in e.g. electricity price and biogas price. A future scenario analysis was also performed using Energy Price and Carbon Balance Scenarios (ENPAC) tool. Retrofitting a gas upgrading system which uses a water scrubber was found not to be economically feasible, mainly due to high costs for desorbing CO2. A process where raw gas is fed to the Sabatier reactor directly was found to be a cheaper alternative, however only profitable for low electricity prices together with high biogas prices or where the investment pay back time was set to its assumed technological life time instead of the assumed economic life time. The case of building a new upgrading system with an amine scrubber was not simulated but investigated using data from literature. The economic performance of this process option was similar to raw gas methanation process. For future studies, it would be important to focus more on the operation of the Sabatier reactor (e.g. controlling the temperature profile) and also look further into optimally utilising the heat from the strong exothermic reaction.