Kinetic modelling of fluidized bed biomass gasification integrated with steam electrolysis for synthetic methane production =

A process configuration for the production of synthetic natural gas (SNG) starting from woody biomass is proposed and analyzed. A kinetic rate model was developed to simulate the gasification of biomass in a bubbling fluidized bed (BFB) gasifier with a mixture of oxygen and steam as gasifying agent. The model has been then validated comparing its predictions with the experimental results reported in the literature and with the predictions of another model, used as a reference. The gasification stage performance, in terms of outlet stream composition and temperature, have been then analyzed by varying some parameters like equivalence ratio (ER) and steam-to-biomass ratio (SBR). Proper values of ER and SBR have been set to maximize hydrogen content within the produced syngas. A solid oxide electrolysis cell (SOEC) system for water splitting has been then modeled. Hydrogen produce at cathode side is mixed with the syngas exiting the gasification unit, to reach the stoichiometric syngas composition for the subsequent methanation reaction, where carbon monoxide and carbon dioxide are hydrogenated in a catalytic reactor to produce synthetic methane. Oxygen-steam mixture from anode outlet is exploited as gasifying agent within biomass gasification unit. A simple approach for the syngas cleaning was used to take into account all the downstream equipment used to reduce the contaminants (e.g., tars, ammonia, hydrogen sulfide and hydrogen chloride) content in the raw syngas before the methanation unit. The whole process has been modeled and analyzed using ASPEN Plus process simulator integrated with an external Fortran subroutine to represent properly the gasification stage in terms of hydrodynamics and reaction kinetics.