Mesoscale bubble dynamics in the gasifier of a 1MWth dual fluidized bed gasifier for biomass gasification

Abstract

Via the multiphase particle-in-cell method, the gasification of biomass feedstock in a pilot-scale dual fluidized bed gasifier is simulated to study the dynamical behavior of mesoscale bubble structure in this complex apparatus. After comparing the simulated data with the experimental results, the flow dynamics of rising bubbles together with the quantitative assessment of bubble properties in the gasifier are studied. The results observe that: (i) different from the traditional bubbling fluidized gasifier, two preferential rising paths of the bubbles exist due to the special gasifier geometry and the gasification of biomass; (ii) bubbles generated above the biomass inlet have the largest chord length along the depth direction and vigorous lateral motion. Bubbles close to the left side wall and newly generated above the biomass inlet have an apparent large rising velocity; (iii) the presence of biomass inlet reduces the bubble temperature by a value of 50 K and increases the bubble density with a value of 0.05 kg/m3 near the biomass inlet. The large thermal property of rising bubbles appears along the right path, while the large mass fraction of the gaseous product exists for bubbles along the right path.