Tray columns 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. 

The incidence of inverse response depends on column internals and vapor rates. It has been suggested (362) that inverse response may occur with valve trays at all vapor rates, while sieve trays may give inverse response at low rates, direct response at high rates, and effectively dead time at intermediate rates. It is unknown whether columns operated in the spray regime experience inverse response in principle they should not, since tray liquid holdup is unaffected by vapor flow rates within this regime (204, 244). 

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... 

It is worth emphasizing that Eqs. (13-61) to (13-68) hold regardless of the models used to calculate the interphase transport rates and EJ. With a mechanistic model of sufficient complexity it is possible, at least in principle, to account for mass transfer from bubbles in the froth on a tray as well as to entrained droplets in a spray, as well as transport between the phases flowing over and through the elements of packing in a packed column. However, a completely comprehensive model for estimating mass-transfer rates in all the possible flow regimes does not exist at present, and simpler approaches are used. 

Solid or fluid particles (bubbles or drops) suspended in another fluid are moving in a large-scale flow. Such a flow can be present in fluidized beds with gas or liquid as continuous phase, for instance dryers, adsorbers, or crystallizers. Fluid particles are moving in bubble or drop columns or in froth (spray or bubble regime) present on coliunn trays. 

---