Hydrodynamic behavior of binary mixture of solids in a triple-bed combined circulating fluidized bed with high mass flux

Flow behaviors of binary mixture of silica sand and nylonshot (coal char substitute) were investigated in a triple-bed circulating fluidized bed (TBCFB) as a cold model of coal gasifier. The TBCFB consisted of a downer (φ 0.1 m × 6.5 m), a bubbling fluidized bed (0.75 m × 0.27 m × 1.9 m), a riser (φ 0.1 m × 16.6 m) and a gas-sealing bed (GSB, φ 0.158 m × 5 m). The initial fraction of the nylonshot in the solid mixture (X _nylon,i) was 15.4 and 30% on mass and volume bases, respectively, or otherwise, 30.7 and 50%. The maximum solids mass flux (G_s) at X _nylon,i of 15.4 and 30.7 wt% were 394 and 349 kg/m² s, respectively, when the gas velocity in the riser (U_gr) was 10 m/s. Apparent solids holdups of silica sand and nylonshot were calculated separately from the static pressure gradient across the riser and the downer. The results showed possibility of large-mass-flux circulation of char in the gasifier, which plays a significant role in decomposition of tar from pyrolysis as the primary step of gasification. A newly developed pressure balance model successfully predicted G_s of the binary mixtures in TBCFB.