Exergy and energy analysis of biogas upgrading by pressure swing adsorption. Dynamic analysis of the process

The aim of this work was to provide a complete exergy and energy analysis of a biogas upgrading technology: pressure swing adsorption. This technology has going to be widely used in Europe, because allowed to reach very high methane recovery (93.4%) and Wobbe Index (50.81 MJ/m3 STP) values. In this study, the upgrading process has been implemented in Aspen Plus and Aspen Adsorption dynamics simulation environment and the biogas was upgraded to biomethane, meeting the UNIT/TS 11537:2019 standards for Biogas to be injected in the gas grid. The upgrading technology has been analysed in terms of process efficiency, also considering CH4 total loss, energy and utilities requirements in dynamic conditions. Each units of the simulated process have been analysed calculating total exergy feed, total exergy produced and exergy loss, distinguishing that lost for irreversibility and as waste. The obtained CH4 recovery at steady cycle state was 93.4%, the CH4 purity in the obtained biomethane was 97.13% whereas the productivity reached a value of 0.143 kg/h·kgads reaching an overall exergy efficiency of 88%.