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 (phi 0.1 m x 6.5 m), a bubbling fluidized bed (0.75 m x 0.27 m x 1.9 m), a riser (phi 0.1 m x 16.6 m) and a gas-sealing bed (GSB, phi 0.158 m x 5 m). The initial fraction of the nylonshot in the solid mixture (X-nylon,X-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,X-i of 15.4 and 30.7 wt% were 394 and 349 kg/m(2) 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. Crown Copyright (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. All rights reserved.