Info

Eq. (6.8)

^ Qd. max

94%

84%

84%

100 x Qo/Qp,

•Center-to-side flow. tSide-to-center flow.

•Center-to-side flow. tSide-to-center flow.

Comment The column still appears oversized. It is now limited by the flow path length in the bottom section. Therefore, any further reductions in diameter require going from a two-pass design back to a single-pass design in the bottom section. Going for a single-pass design will roughly double the liquid load QL (because the weir length will be halved). The resulting liquid load, roughly 15 gpm/in of weir, will be outside the recommended maximum of 7 to 13 gpm/in of weir (1). One way of overcoming this problem is by going to a swept-back weir (1), which in essence lengthens the weir at the expense of losing some bubbling area. This may permit reducing column diameter from 6 to 5.5 ft. For the sake of avoiding repetitious calculations this will not be done here. The reader is urged to attempt a redesign with a 5.5-ft-diameter column (based on the above) as an exercise.

Flooding check—alternative correlation. If desired, the column capacity can be checked using an alternative flooding correlation. This step is optional during column sizing. In this case, this check will be performed using Fair's correlation (Sec. 6.2.6). No derating is applied, as the surface tension correction term will automatically derate high-pressure systems such as the depropanizer.

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