Gas distribution characteristics for heterogeneous flows in the slender particle-containing scrubbing-cooling chamber of an entrained-flow gasifier

摘要

Dual-tip conductivity probes and a high-speed camera were used to study the gas distribution characteristics in a cold model apparatus of the slender particle-containing scrubbing-cooling chamber. The three-dimension column was 200 mm in internal diameter and 1353 mm in height. The effects of superficial gas velocities, fiber volume fractions and fiber aspect ratios on global gas holdups were determined. The results showed that under the influence of reverse buoyancy and negative pressure gradients, plume gas flow went up along the outside of the downcomer in downcomer spout region. Local radial gas holdup which was closely related with the internals and flow patterns presented obviously proximate core peak distribution in bubble-breaking plate region. The foam region consisted of bubble coalescence and breakup as well as droplets formation and splashing. At higher gas velocities, the increasing rate of global gas holdup gradually reduced. With the increase of fiber volume fraction, global gas holdup slightly increased at low gas velocities due to suppressed bed turbulence and bubble loading, but decreased at high velocities for increased liquid viscosity and vortex-shedding. Due to suppressed small-scale velocity fluctuation, global gas holdup increased with increased fiber aspect ratio. A modified drift-flux model containing crowding factor and fiber number density for global gas holdup correlations was proposed and all of the data could be calculated with a relative deviation less than 10%. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.