Influence of biomass particle size on bed agglomeration during biomass pyrolysis in fluidised bed

Bed agglomeration in fluidised bed was recently discovered to be an important consideration during biomass pyrolysis under the conditions pertinent to bio-oil production. The results in this study show that biomass particle size has a significant effect on bed agglomeration during biomass fast pyrolysis at 500 °C. Sand loading, which is defined as the mass of sand sticking to the biomass particles normalised to the total mass of biomass fed, is used for quantifying the interaction between the pyrolysing biomass particle and sand in fluidised bed to form bed agglomerates. Under the experimental conditions, at biomass particle sizes ≤430 µm, sand loading increases with increasing biomass particle size. At biomass particle sizes >430 µm, sand loading decreases with further increase in biomass particle size. The results further show that mass transfer of the sticky agent produced from biomass pyrolysis plays a key role in bed agglomeration. At small particle sizes (≤430 µm), sand loading is dominantly influenced by convective mass transfer of sticky agent while at large particle sizes (>430 µm), sand loading is mainly controlled by diffusive mass transfer of sticky agent within the pyrolysing biomass particle.