NUMERICAL COMPUTATION OF HYDRODYNAMIC BEHAVIOR OF BIOMASS PARTICLES IN CIRCULATING FLUIDIZED BEDS

A model using a particle based approach is developed to accurately predict the hydrodynamic behavior of biomass particles in CFBs. Generally, the change in the pressure gradient with height in CFB riser is small. Numerical results are in good agreement with experiments, both in form and magnitude. In the present study a dynamic two dimensional model is developed considering the hydrodynamic behavior of biomass particles. The bottom zone in turbulent fluidization regime is modeled in detail as two-phase flow which is subdivided into a solid-free bubble phase and a solid-laden emulsion phase. In the upper zone core- annulus solids flow structure is established. Simulation model takes into account the axial and radial distribution of voidage, velocity and pressure drop for gas and solid phase, and solids volume fraction and particle size distribution for solid phase. The model results are compared with and validated against experimental data given in the literature for axial pressure profile along the bed height (Huang et al., 2006). Simulations are performed with different gas velocities at different solids mass flux values. The results are also compared with and validated against experimental data given in the literature for bed pressure drop across the riser against superficial velocity (Abdullah et al., 2003). MODEL DESCRIPTION The model of this paper uses particle based approach which considers the two- dimensional motion of single particles through fluids. According to the axial solid volume concentration profile, the riser is axially divided into the bottom zone and the upper zone.