A novel model of a double fluidized bed steam gasifier for biomass and solid recovered fuel co-gasification

Steam gasification performs the thermochemical conversion of bio-residues or waste materials into a syngas strongly increasing hydrogen concentration (more than 30 % vol). Given the high-technological maturity of gasification process, techno-economic assessments of larger systems integrating gasification with downstream syngas upgrading to biofuels or biochemicals are essential to evaluate economic competitiveness against conventional pathways. However, the models of gasification processes often fail to accurately capture the formation and the destruction of the tar along the reactor. A novel Aspen Plus model of a steam-based dual fluidized bed (DFB) gasifier has been developed with the objective of assessing the process of co-gasification of woody biomass and Solid Recovered Fuel (SRF), focusing on the aspects related to the quality of the syngas quality and of production/destruction of tar. The model integrates hydrodynamic insights from a MATLAB cold-flow simulation of a Güssing-type DFB reactor and has been validated against industrial data. Sensitivity analyses have been performed on the temperature, showing a positive impact on tar reduction and char conversion, while preserving the syngas composition. With respect to the base case, mixing SRF with biomass in the range between 0 and 50 wt% has demonstrated a negative effect on tar destruction, yielding a 52 % rise in the tar concentration in the raw syngas. In contrast, the syngas composition has shown increased hydrogen and methane contents, reaching up to about 45 vol% and 20 vol%, respectively, along with a corresponding decrease in carbon oxides.