Structured-type packing, liquid holdup

For structured-type packing, a liquid holdup of 4 to 5 percent corresponds to this optimum packing fractionation efficiency. For 1-in Raschig rings, this optimum holdup would be roughly 10 to 12 percent. 

The hydraulic operation of structured packings with countercurrent gas and liquid flows is somewhat different than that of random dumped packings. The wire-gauze type is wetted by capillary action, so that the entire geometric surface area becomes available for mass transfer at low liquid flow rates. Thus, Sulzer BX packing was found to have 2 A times the static liquid holdup of Flexipac 2 or Gempak 2A sheet metal types of structured packings [14]. However, once the surface is completely wetted, capillary action has only a small effect as the liquid rate increases. 

Figure 4-8b shows a comparison between the experimental data hp exp for type X structured packings and for stacked 25—50 mm metal Bialecki rings and the liquid holdup calculated using method (4-32), with a packing constant of Cp = 0.465, acc. to Eq. (4-33b). The experimental data is spread around the graph in the flow range of Rep = 2 to Rep 100 with a relative deviation of 8(hp) < 15%. 

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