Bubble size, continuous settling

Dispersions may be classified into two types, based upon size range of the droplets formed. Turbulence creators (mixing impellers, mixing valves, eductors, orifice plates) will produce fine emulsions of micron-size droplets. Nozzles, perforated plates, bubble caps, tower packings, etc., can form discrete drops of relatively large size which will quickly settle through the continuous phase. 

It only operates in continuous mode and uses catalyst particles of a slightly larger size than in BCR an upward flow of L maintains S in suspension, but the L velocity should be slower than the S settling velocity. Stability also requires a very narrow particle size distribution. Hydrodynamics and mass transfer depend on G/L flow ratio. G velocity is usually rather slow, with bubbles rising through a continuous L phase. Heat removal is restricted to use of wall exchangers. 

Drop doesn t settle] [density difference decrease] /[viscosity of the continuous phase increases] /[drop size decreases] /[residence time for settling too short] / [phase inversion or wrong liquid is the continuous phase] /pressure too low causing flashing and bubble formation. 

Successful application of dispersion-solids sedimentation models in continuous bubble column reactors has been achieved but it also has been shown that the solids sedimentation effects rapidly decrease with reactor diameter. For columns larger than 30 cm, solids settling effects usually can be neglected for particle sizes up to 200 pm. 

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