Abstract
The cold flow hydrodynamics and segregation characteristics of a binary mixture of high-ash coal and sand have been investigated in a dual fluidized bed(DFB) gasifier. A short riser, maintained in the fast-fluidized bed regime by different combinations of primary and secondary aerations, is used. The influence of fluidization velocities, secondary-to-primary aeration ratio (φ), particle mixture properties has been examined on the full-loop pressure profile, solids circulation rate (Gs), and segregation characteristics. A substantial influence on DFB pressure profiles is observed for the polydisperse binary mixture compared to unary sand particles having a narrow particle size distribution. Coarse particle fractions measured at loop-seal and pot-seal indicates significant segregation in the riser and the BFB, which reduces as fluidization velocities increase. Variations in Gs and φ show a minimal impact on particle segregation. No reverse gas bypass is detected for the designed operating parameters through solids recycle valves, namely loop-seal and pot-seal. Except for some discrepancies observed at high superficial velocities and Gs, the values of axial solids holdup in the riser yield a reasonable agreement between experiments and a hydrodynamic model based on empirical correlations.
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