Integration between biomass gasification and high-temperature electrolysis for synthetic methane production

Abstract

The energy system analysis of an integrated process producing synthetic natural gas (SNG) from woody biomass has been carried out. Two different process configurations have been proposed and modeled, considering the integration between biomass gasification, solid oxide electrolysis (SOEC) and catalytic reactors for methane synthesis. The two investigated process configurations differ in the size of the SOEC unit. In the first configuration, the electrolysis unit is sized to increase H2 content in the produced syngas to satisfy the methanation reaction stoichiometric requirement. In the second configuration, electrolysis provides to the gasifier the requested amount of oxygen. For this second configuration, an additional section composed of 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 condition. The gasifier has been modeled and studied to choose the gasification parameters' appropriate values, as equivalence ratio and steam-to-biomass ratio, and their impact on gasification outlet temperature and syngas composition. The whole process has been analyzed from a thermodynamic standpoint. After a thermal integration between the streams of the plant, energy efficiency has been calculated for both configurations: the first one (SOEC sized on hydrogen requirement) presented an efficiency of 71.7 %, while the second one (SOEC sized on oxygen requirement) showed an efficiency of 66.8 %.