Umeå universitets logga

After years of development of the dual fluidized bed gasification process with woody biomass, new challenges arise with a wider range of feedstocks, such as agricultural residues or waste fractions, gaining importance. This work presents the results from the operation of a 1 MW advanced dual fluidized bed (aDFB) gasifier at the Syngas Platform Vienna, with cashew shells (CS) as feedstock and pure olivine or olivine mixed with 33% limestone as the bed material. Two operation points, different in their main process parameters, with CS as feedstock were performed for a minimum of 16 h. Due to the high calorific value (22.7 MJ/kg dry) and high content of volatile components (81.7 wt % dry), CS are well suited for gasification. During the operation, a product gas with a H2/CO ratio of 1.93-2.29 was produced, which suits the use of the syngas as input for Fischer-Tropsch synthesis. Due to the low ash softening temperature of CS of about 840 °C, determined in ash fusion tests and predicted by thermodynamic equilibrium calculations, the operating temperature in the gasifier was kept below 820 °C in the first operation point with around 20 h of runtime. Bed material samples after the operation revealed the formation of agglomerates, which were analyzed by SEM and EDS for their morphology and composition. During the second operation point, temperatures in the gasifier were increased to 870 °C for 16 h, while no agglomeration tendencies were observed. Both operations did not show changes in fluidization behavior compared to operations with wood chips (WC). The evaluated key performance indicators were compared to aDFB steam gasification of WC as the reference.