Effect of Tray Maldistribution on Efficiency

Case studies were reported (170,174) of large-diameter ( 15-ft) towers with sieve trays not reaching the expected efficiency. Maldistribution was cited as the culprit or at least one of the causes. Improving liquid flow patterns, often among other modifications, was the fix. The only other evidence that channeling adversely affects tray efficiency comes from the above-mentioned theoretical models. 

Improving liquid flow patterns. A number of special tray designs have been developed to improve liquid velocity distribution on large-diameter trays. Their main applications are vacuum distillation. In pressure distillation, liquid flows are usually high and multipass trays are used, so that stagnant zones are seldom a problem. Some means of improving the liquid flow patterns are 

Using valve trays. Their sideways gas movement alleviates liquid channeling (Sec. 7.3.2, item 9). On the basis of eliminating the stagnant regions, Biddulph (168) expects valve tray efficiencies in 

Using suitably directed slots and bafiles to avoid channeling. Such devices (170,178) have improved efiiciency in large-diameter vacuum towers with long flow paths. Use of these devices in laige-diameter towers has been advocated for vacuum services (24,161) and for pressure services with tall weirs (161). 

Using arc-shaped downcomers. Special tray designs (165,169) have arc-shaped downcomers, which direct liquid toweird the column walls. These devices improve flow patterns, but their effect on efficiency has not been tested. 

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