Tray Sizing Example and Initial Steps

Example a.1 Size the depropanizer from Examples 2.4 (Sec. 2.3.1) and 3.4 (Sec. 3.2.5). The feed rate is 2000 ib-mole/h of mixture. Minimum anticipated load is 60 percent of design. 

Tray area. Using an entrainment flooding correlation is the usual method of calculation, but short-cut methods (e.g., Ref. 10) are often adequate. However, to minimize trial and error, the author prefers to perform the preliminary estimate using the flooding correlation which will eventually be used, with some simplifying assumptions. In this example, the Kister and Haas correlation [Eq. (6.12)] will be used for the preliminary determination of tray area. Make the following simplifying assumptions  

To calculate the bubbling area from the flood velocity, the derating factor is needed (Table 6.7). For depropanizers, SF 0.9 top and bottom. Also needed is a safety margin from flood at this point, assume the column is to be designed for 80 percent of flood. 

Downcomer area. Use Table 6.5 to obtain a preliminary estimate of downcomer top area. For a depropanizer at 315 psia, Table 6.5 recommends a velocity of 90 to 110 gpm/ft2. Select 100 gpm/ft8. No derating is required here, since the factors in Table 6.5 already take the foaming tendency into account. 

Ad = 850/100 = 3.5 ft Tower diameter. Total tower area is given by 

MAXIMUM u Ans Table 6.10 shows that both tiie volumetric and mass v por and liquid flow rates in the top section peak at stage 3. Stage 3 is therefwe the appropriate basis for the maximum throughput calculation ftr Ihe tep section. 

TABLE 6.10 Column Loading and Physical Properties Depropanizer example 6.1 (Basis 20,000 Itemolt/h feed) 

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