Bubbling promoters

Values for the various parameters in these equations can be estimated from published correlations. See Suggestions for Further Reading. It turns out, however, that bubbling fluidized beds do not perform particularly well as chemical reactors. At or near incipient fluidization, the reactor approximates piston flow. The small catalyst particles give effectiveness factors near 1, and the pressure drop—equal to the weight of the catalyst—is moderate. However, the catalyst particles are essentially quiescent so that heat transfer to the vessel walls is poor. At higher flow rates, the bubbles promote mixing in the emulsion phase and enhance heat transfer, but at the cost of increased axial dispersion. 

Air Sparging Gas sparging or injection of air bubbles has been effectively used to reduce concentration polarization and enhance mass transfer. " The secondary flows around bubbles promote mixing and reduce the thickness of the concentration polarization boundary layer. When the bubble diameter exceeds that of the membrane (tubular or hollow fiber), slugs are then formed further increase in bubble diameter has no effect on flux improvement. Large slugs can displace most of the boundary layer and cause the pressure to pulsate. This results in enhancing the flux. 

Electrochemical reactions at the electrodes produce very fine H2 and O2 gas bubbles and highly chemically reactive hydroxyl (OH ) and superoxide (H02 ) radicals. The gas bubbles promote the flotation of coagulated solids and coalesced hydrocarbons, etc. The hydroxyl and superoxide radicals cause precipitation of hydroxides of heavy metals and the breakdown of many soluble organic molecules. 

Figure 6.18 Liode sieve trays (a) slotted sieve tray (b) bubbling promoter, aoss-flow tray. (Fran Chemical Engineering Progress, with permission.)...

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