Packed towers Pall rings

Distillate and bottoms were controlled by accumulator and sump levels, respectively, feed and reflux on flow control and boilup was temperature-controUed Tower pall rings were replaced by higher-capadfy rings (bottom) uid wire-mesh structured packing (top) to increase c )acity and reduce reflux. The column was sensitive to ambient disturbances (e.g., rainstorms). The reflux reductions escalated this sensitivity to an extent that annulled the revamp benefits. The temperature control was ineffective due to its narrow range of variation. Problems were solved by controlling boilup on sump level and bottom product on flow control. 

Tower with packed tubes Pall rings Tower with packed tubes Pall rings... 

On the basis of this better performance of the Pall ring, a smaller diameter tower must be selected and the tower reevaluated based on the new mass flow rates with this packing. The economics require that the higher packing cost, smaller tower diameter, new total packing volume, and tower pressure drop be considered. 

Packed towers are employed when 5-10 stages suffice. Pall rings of 1-1.5in. size are best. Dispersed phase loadings should not exceed 25 gal/(min) (sqft). NETS of 5-10 ft may be realizable. The dispersed phase must be redistributed every 5-7 ft. Packed towers are not satisfactory when the surface tension is more than 10 dyn/cm. 

A packed absorption tower is used to remove S02 from an air stream by absorption in a solvent. The tower is 5 ft in diameter and 60 ft high and contains 1.5 in. plastic Pall rings. The temperature and pressure in the tower are 90°F and 30 psig. The gas stream flow rate is 6500 scfm. The liquids SG is 1.25, and its viscosity is 25 cP. 

Depth of packing without intermediate supports is limited by its deformability metal construction is limited to depths of 20-25 ft, and plastic to 10-15 ft. Intermediate supports and liquid redistributors are supplied for deeper beds and at sidestream withdrawal or feed points. Liquid redistributors usually are needed every 2 -3 tower diameters for Raschig rings and every 5-10 diameters for pall rings, but at least every 20 ft. 

A packed tower with 3 in. metal pall rings will be analyzed for the system of Example 13.15. The packing factor is F = 15 sqft/cuft. 

Packed tower Flooding velocity is obtained with Figure 14.17. For 1 in. metal pall rings,... 

A tower packed with 2 in. pall rings instead of trays ... 

Empirical Prediction Moore and Rukovena [Chemical Plants and Processing (European edition), p. 11, August 1987] proposed the empirical correlation in Fig. 14-64 for efficiency loss due to liquid maldistribution in packed towers containing Pall rings or Metal Intalox packing. This correlation was shown to work well for several case studies (Fig. 14-64), is simple to use, and is valuable, at least as a preliminary guide. 

A tower packed with 2 in. pall rings instead of trays packing volume Vp = ( t/4)(4) (120) = 1508 cuft,... 

The pressure drop in the cooler is obtained directly from using Fig. 2-17 provided by Woods. For Pall rings this would be approximately 0.35kPa/m. Thus, the total pressure drop in the cooler with a length of 1.67 + 0.2 = 1.87 m. (the 0.2 m is added to provide sufficient clearance in the packed tower) is... 

---