Integration of biomass gasification and high temperature steam electrolysis for synthetic natural gas (SNG) production

Two different process configurations for the production of synthetic natural gas (SNG) starting from woody biomass are proposed and analyzed. Both configurations are characterized by the integration of a two-stage gasifier, a solid oxide electrolysis cell (SOEC) and a methane synthesis reactor. They differ in the size of the SOEC unit: in the first configuration electrolysis directly enhances the syngas produced in order to satisfy the stoichiometric requirement of the methanation reaction, while in the second one it provides to the gasifier the requested amount of gasifying agent (oxygen and steam). For this second configuration, an additional section composed by a water gas shift (WGS) reactor and a carbon capture and sequestration (CCS) unit is required to adjust the reacting gas composition and thus to ensure the proper stoichiometry for the methanation process. The two different configurations have been compared at the same gasification conditions. The gasification unit has been studied to choose proper values of the gasification parameters, as equivalent ratio and steam-to-biomass ratio. The processes have been analyzed from a thermodynamic standpoint using Aspen PlusTM. After a thermal integration between the streams of the plant, energy efficiency has been calculated for both configurations: the first one shows an efficiency of 73,2 %, while the second one shows an efficiency of 68,5 %.