Maldistribution, packings, liquid packing height

Since liquid maldistribution may become a problem unless the flow is periodically redistributed in a tall column, the total packing height must be broken up into a number of individual beds ... 

Very important for all types of packings is a uniform liquid distribution at the top of the bed and a limitation of bed height to 6 or 8 m. Beneath each bed, the liquid has to be collected, mixed, and redistributed. These measures intend to suppress the so-called maldistribution of liquid because it strongly affects mass transfer rates. The design of liquid distributors, liquid collectors, support grids, etc., should provide a large open area not to hinder the countercurrent flow of gas and liquid. 

Fig. 5.4-24 Maldistribution in a packed column (metal Pall rings 35 mm). Column diameter D = 0.63 m, packing height H = 6.8 m. Gas load F = 1.1 Pa, liquid load B = 5.2 w /(jn -h). Ley Uniform liquid feed. Rigte Single point liquid feed...

The smaller the reflux ratio, the more the separation effect decreases with maldistribution. To restrict maldistribution of the liquid by channeling or flow at the wall, the total height of the packing Z is separated into single packing heights Z. each with its own support and cover grids, and liquid distributor [2.118]. 

It may be that the random or structured packing efficiency is degraded by the need to limit the bed-height space required for liquid collection redistribution, and by maldistribution and channelling in the packing [33]. 

The maximum bed height that should be used without liquid redistribution depends on the type of packing and the process. Distillation is less susceptible to maldistribution than... 

Liquid maldistribution tends to lower packing turndown (221, 386, 387). The "standard distributor curve in Fig. 3.1 depicts typical variation of packing HETP (height equivalent of a theoretical... 

A imiform distribution of the liquid and vapour phase over the entire cross-section (3) is crucial for the efHciency of the separation. Even if the liquid is initially distributed in a uniform way, its maldistribution increases with the covered distance. Therefore, the height of a packing bed is limited to about 3-6 m. The liquid is collected at the bottom of the packing bed, is mixed and is uniformly redistributed by means of a distributor onto the top of the next packing bed. 

Too low a liquid flow rate is not a fatal flaw but does cause channeling and maldistribution of the liquid, much as it does in packed columns. The remedy here is to set a lower limit on weir crest height of 0.5 cm, equivalent to 2 m /h of liquid flow per meter weir length. 

---