being designed so that upflow-ing vapor and downflowing liquid pass through the same orifices. This mixture Already a Chemical Engineering member? Weeping point: refers to a condition when the vapor velocity through the perforations of a tray is so low . If any of the foregoing contributors level on the j becomes excessive (for instance, too tray be- > much head loss under the downcomer or aeration due to foaming), liquid will back up in the downcomer and spill onto the tray. The higher pressure drop and liquid flowrate backs liquid higher into the downcomer until liquid spills onto the tray above. Thus, improved separation at higher throughput may indicate a weeping problem. Affecting Operation, Other Limiting the hole area to 13-14% prevents weeping in distillation columns. Although not as ! stacking up liquid on the upper tray. One useful test is to increase the column feedrate while monitoring the column pressure drop and the reflux rate required to maintain the separation. i dont think there will be anycorrelation for calculating channelling in the packed bed but in order to avoid it you have to restrict the packing bedheight. This differs from what occurs in the packed column, where the wetted packing provides much of the surface area for mass transfer. In addition to that, the excessive liquid present in the downcomer or froth levels causes flooding and loss of efficiency of the tray of the tower. This course is designed to provide you with a complete understanding of construction details and the functioning of distilling columns. Special valve designs provide additional turndown. weep-proof as bubbie-cap trays, valve i trays can be turned down to about 20Tc i of maximum capacity without weeping ! The flow patterns on a tray of a distillation column with gas rising continuously through the downflowing liquid are pretty complex. Because of the empirical character of flooding correlations, a predicted value of 80% flooding may correspond to actual flooding flowrates. Distillation and Unit Operation Control & Troubleshooting (8) zWhen flooding starts on a tray, all the trays above that point will also flood, but trays below that point will go dry . Entrainment is expressed as kg (droplet entrained)/s, kg/kg vapor, kg/kg liquid flow, or kmol/ kmol liquid flowing. heat exchanger. The clearance problem was mainly attributed to scale left on the tray support rings during the installation of new panels that raised the height of the tray panels. generally distributed onto a distillation tray via a weir. Sieve trays offer higher capacity with lower pressure drop and entrainment than do bubble-cap trays. For trays of the distillation tower, the incipient flood point corresponds to the best efficiency point. Resources, Copyright 0000002463 00000 n (: Distillation columns) . Once tray-2 floods, downcomer C (shown in Fig. Such maldistribution of the gas or the vapor called vapor channeling severely reduces tray efficiency. where crest height = inches of the level of clear liquid overflowing the outlet weir; GPM = gallons (U.S.) per minute of liquid that leaves from the tray. Design of Distillation Columns (1).pdf - yumpu.com D. Results due to very low gas velocity. At lower flow-rates. This sensitivity to liquid rate suggested a liquid flow-path problem, such as downcomer flooding. Weeping usually subsides with higher flowrates. FIGURE 1.
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