Tower pressure drop, flooding

Revised Packed Tower Pressure Drop Correlation Constants for Towers Operating Below Flooding Region... 

The most conservative definition of vapor flooding capacity is the load for which tower pressure drop exhibits a sharp increase, signifying liquid buildup at some tray. It is, however, possible to operate the tower at somewhat higher load, perhaps 10% more. As the load is increased, reboiler pressure rises, allowing a semistable operation, albeit with reduced separating... 

The tower was flooding. Any time reduced fractionation coincides with increased tower pressure drop, incipient flooding is indicated. To confirm this conclusion, I increased the LCO internal reflux rate and observed that the Magnehelic reading increased and the LCO product color darkened. 

If overall tower pressure drop is too low from the flash zone to the top then there may be damage to the tower internals or hydraulic problems. If the pressure drop is too high then flooding, plugging or internal damage may be indicated. 

Capacity factor based on tower area, ft/sec Capacity fector at flood, ft/sec Liquid gradient vapor load correction factor or Discharge coefficient (see accompanying table) or Gas phase loading factor, ft/sec. Equation 8-281 Eddy loss coefficient, dimensionless. Table 8-22 Wet cap pressure drop correction factor. Figure 8-115... 

Figure 9-21D. Loading, flooding and pressure drop coireiation (one of earlier versions). Adapted by permission from Leva, M. Tower Packing and Packed Tower Design, 2nd ed. U.S. Stoneware Co.

To complete the design, the tower should be checked for loading and flooding conditions, and the pressure drop established. However, this procedure will not be repeated as it can be found elsewhere in this text. 

Elgin, J. C. and Foust, H. C. Ind. Eng. Chem. 42 (1950) 1127. Countercurrent flow of particles through moving continuous liquid pressure drop and flooding in spray-type liquid towers. 

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