Flood trays physical properties

TABLE 14-13 Dependency of Distillation Flood Velocity on Physical Properties and Tray Open Area... 

Kister and Haas [184] recommend using 25 dynes/cm in Equation 8-286 when the actual surface tension is a 25 dynes/cm. This correlation is reported [94, 184] to give better effects of physical properties, and predicts most sieve and valve tray entrainment flood data to 15 to 20%, respectively. 

Entrainment flooding is predicted by an updated version of the Souders and Brown correlation. The most popular is Fair s (1961) correlation (Fig. 20), which is suitable for sieve, valve, and bubble-cap trays. Fair s correlation gives the maximum gas velocity as a function of the flow parameter (L/G)V(Pg/Pl), tray spacing, physical properties, and fractional hole area. 

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. 

It gives a close approximation to the effects of physical properties, operating variables, and tray geometry on the flood point. This is a major improvement compared to the previous correlations above. 

Forty years ago these computed variables were calculated using pneumatic devices. Today they are much more easily done in the digital control computer. Much more complex types of computed variables can now be calculated. Several variables of a process can be measured, and all the other variables can be calculated from a rigorous model of the process. For example, the nearness to flooding in distillation columns can be calculated from heat input, feed flow rate, and temperature and pressure data. Another application is the calculation of product purities in a distillation column from measurements of several tray temperatures and flow rates by the use of mass and energy balances, physical property data, and vapor-liquid equilibrium information. Successful applications have been reported in the control of polymerization reactors. 

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