Flood-Point Definition

Flood-Point Definition In 1966, Silvey and Keller [Chem. Eng. Progr. 62(1), 68 (1966)] listed 10 different flood point definitions that have been used by different literature sources. A later survey (Kister and Gill, Proceedings of Chemeca 92, p. 185-2, Canberra, Australia, 1992) listed twice that many. As Silvey and Keller pointed out, the existence of so many definitions puts into question what constitutes flooding in a packed tower, and at what gas rate it occurs. Symptoms used to identify flood in these definitions include appearance of liquid on top of the bed, excessive entrainment, a sharp rise... 

Some unique considerations associated with flood-point definition apply to the grid charts only (10.8005 to 10.8108 only). These are described in Sec. 8.2.6 and should be consulted before interpolating flood data on those charts. 

The exact definition of the flood point in packed towers is uncertain. Silvey and Keller (367) list ten different flood point definitions which were used by different investigators. Perhaps the most popular definition is (51, 319) "the vapor velocity above which liquid accumulates uncontrollably in the packed bed and continued operation becomes impossible. ... 

Kister and Gill (60,60a) demonstrated that despite differences in definitions, flood-point data compared quite well to correlation predictions. Both Kister and Gill (60,60a) and MacDougall (53) show that flood data from various sources (using various definitions) can be correlated to with 10 to 15 percent accuracy. It was also demonstrated that the flood point can be predicted far more reliably than packing pressure drop (55,58) and maximum operational capacity (60). 

Fig. 6 includes full-scale capacify dafa for 3, 4, and 6 in. caps at low pressure obtained by FRI and by Shell for 6 in. caps only (Fractionation Research, Tulsa, Oklahoma, U.S.A., private communication). Both sets of data for 6 in. caps show a capacity deficit compared to the smaller caps however, the Shell data show approximately 80% of the capacity found by FRI. The difference may be caused by system properties or by the more conservative definition of flood point used by Shell. Data at higher pressure with the butane-isobutane system at the 4 ft diameter were also obtained by FRI (Fig. 8). 

At total reflux (L/V) = 1) Capps found several points in the FRI data that corresponded with this [241] definition of ultimate capacity, i.e., the liquid and vapor load at which any increase in either liquid or vapor would induce flooding by at least one of the following mechanisms ... 

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