Numerical evaluation of multi-scale properties in biomass fast pyrolysis in fountain confined conical spouted bed

Abstract

Biomass fast pyrolysis is one of the promising ways to convert cellulose and lignin into available biochar, bio-oil and product gases. In the current work, the process of biomass fast pyrolysis is numerically studied via the reactive multiphase particle-in-cell (MP-PIC) model in a conical fountain confined spouted fluidized bed to investigate gas-solid motion (e.g., gas and solid fluxes) and particle-scale characteristics (e.g., particle velocity, residence time, temperature, heat transfer coefficient and dispersity). Simulation results have been well validated with experimental data. Biomass and sand behaviors in scenarios with and without fountain confiners have been comprehensively compared. It is recommended to insert a fountain confiner in spouted bed reactor because it can significantly increase the yields of Gas1 and tar of about 115.1% and 118.8%, respectively. The presence of the fountain confiner has resulted in an upward shift of the maximum temperature and HTC for biomass and sand particles, resulting from the enlarged amount of particle accumulation. Due to large temperature difference, biomass and sand particles have highest HTCs at inlet of about 200 W/m2·K and 120 W/m2·K, respectively. The axial dispersion coefficients of biomass and sand particles are two orders larger than the radial one, resulting from distinctive flow pattern in the spouted bed. The axial dispersion coefficients of biomass and sand particles in the fountain confined spouted bed are 1.93 × 10−3 m2/s and 2.40 × 10−4 m2/s, respectively. The relationships between particle parameters in conventional and fountain confined spouted beds are compared. The findings of this study can provide valuable insights into assisting designers in optimizing the design of such reactors.