Spray Entrainment Flooding Prediction

The entrainment flooding prediction methods described here are based primarily on spray entrainment flooding. Considerations unique to froth entrainment flooding can be found elsewhere (Kister, Disfiliation Design, McGraw-Hill, New York, 1992). 

For decades, the Fair correlation [Pet/Chem. Eng., 33(10), 45 (September 1961)] has been used for entrainment prediction. In the spray regime the Kister and Haas correlation was shown to be more accurate [Koziol and Mackowiak, Chem. Eng. Process., 27, p. 145 (1990)]. In the froth regime, the Kister and Haas correlation does not apply, and Fair s correlation remains the standard of the industry. Fair s correlation (Fig. 14—34) predicts entrainment in terms of the flow parameter [Eq. (14-89)] and the ratio of gas velocity to entrainment flooding gas velocity. The ordinate values XF are fractions of gross liquid downflow, defined as follows ... 

When Fair s correlation was developed, little was known about the difference between spray and froth entrainment flooding, and the data base used was small and included both types. The author compared predictions from Fair s correlation to a much wider data bank available at present. The correlation predicted most of these data well, perhaps somewhat on the conservative side. However, the correlation has been less successful ii. reliably predicting some of the effects (described above) of physical properties, operating variables, and tray geometry on entrainment flooding. 

Prediction. Prediction methods for spray entrainment, froth entrainment, and downcomer backup are available in distillation texts and articles (e.g., 73, 193, 201o, 243, 257, 319, 371, 404, 409). Criteria for predicting downcomer choke flooding are discussed in Sec. 6.16. 

A mote accurate (and somewhat mote complicated) correlation for predicting entrainment flooding on sieve and valve trays is proposed by Kister and Haas (1990). Their correlation is also derived from the original work of Souders and Brown, but provides a modified approach for determining Ky. They introduce, as an important parameter in the correlation, the clear liquid height at the froth-to-spray-iegime transition, and suggest that it be calculated by an equation attributed to Jeronimo and Sawistowski 0973). 

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