Column distillation spray regime

In high pressure distillation, tray operation is usually in the emulsion regime. In small diameter (less than 1.5 m) columns, or at low liquid loads, or the low end of the pressure range (towards 10 bar), however, the froth-and spray regimes can be found. 

Column hardware choice can have a significant influence on the conversion and selectivity such aspects can be properly described only by the NEQ cell model, or by a still more sophisticated model based on computational fluid mechanics (such models have yet to be developed). It is insufficiently realized in the literature that, say, for tray RD columns, the tray design can be deliberately chosen to improve conversion and selectivity. Even less appreciated is the fact that the design methodology for RD tray columns is fundamentally different from that of conventional trays. Liquid residence time and residence time distributions are more important in RD. The froth regime is to be preferred to the spray regime for RD applications this is opposite to the design wisdom normally adopted for conventional distillation. For relatively fast reactions, it is essential to properly model intra-particle dif... 

In atmospheric and low-pressure (<100-p i) distillation, the column is likely to operate in the froth regime, but depending on the liquid and vapor rates, it may also operate in either the spray or emulsion regime. 

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