Describing Mass Transfer in Circulating Fluidized Beds by Ozone Decomposition

Olav Bolland and Rainer Nicolai
The objective of this work was to improve understanding of the mass transfer between gasand solids in the riser section of a gas-solids circulating fluidized bed (CFB). In order toexperimentally investigate gas-solids mass transfer in a CFB, a suitable low-temperaturemass transfer process was applied: the decomposition of ozone (O3) using particles ascatalyst. Particles used were angular cast steel with an average diameter (mass mean) of134µm. The experiments were carried out in a semi-industrial sized CFB. Operatingconditions were varied, with superficial gas velocity of up to 7.2 ms-1 at 60 °C risertemperature, and riser net solids mass flux up to 53 kgs-1m2. The overall solidsconcentration was around 2-2.5% and about 10% in the lower part of the riser. Ozoneconcentration profiles, axial pressure profiles, solids net mass flux as well as local particlevelocities were measured. Gas velocity profiles were assumed in order to calculate the totaltransport of ozone at different heights in the riser. The importance of the lower part of theriser with respect to mass transfer is shown.

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