Single particle model for biomass pyrolysis with bubble formation dynamics inside the liquid intermediate and its contribution to aerosol formation by thermal ejection

- A new biomass pyrolysis particle model was developed.
- The model accounts for mass/energy transfer and population balances for a bubbling liquid intermediate.
- Model simulates evolution of the liquid phase within the solid matrix and aerosol ejection when it reaches surface.
- Effect of particle size, temperature and heat transfer rate impacted bubbling dynamics and aerosol ejection.

A mathematical model for biomass pyrolysis was proposed which couples mass and energy balances with the chemical reactions responsible for the generation of key species. The model includes volumetric particle shrinking and the explicit consideration of secondary reactions. Most importantly, for the first time this particle model includes the evolution of the liquid phase trapped within the solid and aerosol ejection due to bubbles bursting at the particle surface. Bubbles size distributions were estimated by population balances of dynamic bubbling in the liquid phase using the momentum method for calculations. The model was used to evaluate the effect of particle size, temperature, heat transfer coefficient, and reaction time on products distribution. Both bubble bursting and aerosol ejection intensity increased as particle thickness decreased and the heat transfer coefficient was augmented. The model shows how biomass thickness, external heat transfer coefficient, and temperature impact the yields of aerosols, char, and gas. The highest calculated yield of aerosols was 25 wt.% and was obtained with external heat transfer coefficients corresponding to fluidized bed (1000 W/m2 K) with a 1 mm particle. At lower heating rates (50 W/m2 K), the yields of aerosols (10-15 wt.%) were lower than those obtained at high heating rates.