Pressure Drop Inherent Limitations and Traps

Pressurs drop This is often used to specify packed tower capacity. The application of this criterion, and the interpretation of packing pressure drop data are not trouble-free. Some inherent limitations and traps are 

Diy-packed beds have h er pressure drops than wet-packed be. Billet (56) and Kister (40) report cases where changing Cram diy to wet packing increased column capacity by 6 percent and reduced pressure drop by 10 percent. Ludw (63) reports cases where this pressure drop reduction was 50 to 60 percent. The 

Pressure drop is a function of vapor and liquid velocities, densities, and physical properties. The velocities and densities vary with changes in compositions along the packed bed. For test systems where these variations are large, pressure drop data may contain significant errors. 

In some cases (65), it has been observed that nonuniform liquid distribution can lead to lower pressure drop than under tuiiform distribution. MacDougall (58) postulated that liquid maldistribution can generate gas maldistribution, which in turn will affect pressure drop. MacDougall extended this argument to cast suspicion on pressure drop data measured at Uquid rates be- 

Plastic and thin-waU m al packings d ect with time and tem-perature and compress. The problem is aggravated in tall beds and where a plastic s proaches its maximum use temperature. The compression raises pressure drops. The rise in pressure drop, however, is general snialler than t t due to ceramics breakage. 

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