Packing selection

Packing Selection and Performance Guide Lines Trays versus Packings... 

Eckert [125] provides some basic guidelines to good packing selection for various system performance requirements. Kunesh [126] illustrates the often-determined pressure drop advantage of random packed towers over the usual valve tray. See Figure 9-19 [126],... 

Figure 9-24A. Packing factors (stacked packing selected grids). Used by permission of Morris and Jackson, Absorption Towers But-terworth Scientific Publications, and imperial Chemical Industries, Ltd., and adapted by U.S. Stoneware Co. (now, Norton Chemical Process Products Corp.).

Detailed tower sizing for diameter and height iterate on packing selection until overall design criteria are met. 

In any event, the optimum number of pour points per unit of tower cross section depends on the type and size of packing selected, and also on the practical limits of distributor design and... 

The above has to be established by laboratory testing prior to a formal stability programme. As with all pack selections, detailed knowledge of the product, the packaging materials and the process to be employed is an essential requirement. Blister packs are unlikely to give sufficient protection to products severely affected by moisture, oxygen, carbon dioxide, as all known plastic materials are to some degree permeable to these factors. 

The foregoing suggests that column diameters and packing selection can be sased on pressure drop and, indeed, this is commonly done. Figure 16.15 shows die computational steps. We start with the L/C obtained from the material iialance, choose a preliminary packing size, and obtain F from Table 16.6. Next we decide on the AP. A reasonable value for absorbers and strippers is 0.4 in./ft, which, as shown in Fig. 16.16, corresponds to about 60 to 70% of capacity [flooding). 

If a more accurate estimate of packed height is desired, correlations of experimental mass-transfer coefficients or heights of transfer units should be used for the particular packing selected. Some of these correlations are provided in simulators and the method of calculation is given in detail by Seader and Henley (1998). 

The physical properties of the fluids give the Schmidt and Prandtl numbers as well as the heat capacities in the last terms. Process data give the flow rates G and L. Mass-transfer data for the packing selected for the application give the values of //g,d and as functions of the other quantities. It is best to use the latest manufacturers data to characterize packing. 

Trace enrichment (TE) is a sample preparation technique using a minicolumn filled with a packing selected for its properties of attracting wanted components while eliminating unwanted ones. It is connected to the valve ahead of the analytical column, which traditionally is used only for sample injection. The sample solution is pumped (with a second pump) onto the TE column in one mobile phase, and usually washed with a second mobile phase to elute some unwanted components. Then, with a change in the flow path, it is backflushed to place the sample at the head of the analytical column, where separation begins. This speeds up the complete analysis, avoids many interferences for unwanted impurities, and when automated, runs unattended. 

Three HiGee units were installed by Dow Chemicals in the US for stripping hypochlorous acid, used as the reactive chemical in a process. The rotating packed-bed used for stripping was selected after other alternatives such as a spray distillation tower were rejected for capital cost reasons. The packing selected was a woven wire screen, with the gas flowing counter-current to the liquid. Various packing surface areas were tested, with 2000-3000 m /m area densities, but these exhibited no performance differences so the lower value was used. 

These proprietary solutions still exhibit some foaming tendencies therefore, the column diameter should be chosen for a maximum pressure drop of 0.25 in. H20/ft with the packing selected. The physical properties of these solvents can be obtained from the process licensor. 

Kq2l value for 2 plastic Super Intalox packing to KqZ. value for the packing selected as shown in Table 5-5. The packed depth required also is inversely proportional to the relative KqS. values corrected for liquid rate, as given in Table 5-6. 

Because the volume of aqueous feed solution is much greater than the volume of solvent, the water phase will be dispersed into the solvent phase in order to generate the maximum interfacial area for mass transfer. The packing selected will be 40IMTP packing, which will be wetted initially with solvent. From Table 11-4, this packing has a surface area of 46 ft /ft, and the void fraction is 0.972. 

The height of the tower will depend on the type of packing selected, the tower diameter and the extent of pressure drop allowed see Example 8.1.1. 

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