Abstract
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 0.1m×6.5m), a bubbling fluidized bed (0.75m×0.27m×1.9m), a riser (ϕ 0.1m×16.6m) and a gas-sealing bed (GSB, ϕ 0.158m×5m). The initial fraction of the nylonshot in the solid mixture (Xnylon,i) was 15.4 and 30% on mass and volume bases, respectively, or otherwise, 30.7 and 50%. The maximum solids mass flux (Gs) at Xnylon,i of 15.4 and 30.7wt% were 394 and 349kg/m2s, respectively, when the gas velocity in the riser (Ugr) was 10m/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 Gs of the binary mixtures in TBCFB.
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