Tray efficiencies experience factors

Factors Affecting Tray Efficiency Below is a summaiy based on the industry s experience. A detailed discussion of the fundamentals is found in Lockett s book (Distillation Tray Fundamentals, Cambridge University Press, Cambridge, England, 1986). A detailed discussion of the reported experience, and the basis of statements made in this section are in Kister s book (Distillation Design, McGraw-Hill, New York, 1992). 

Experience Factors These are tabulations of efficiencies previously measured for various systems. Tray efficiency is insensitive to tray geometry (above), so in the absence of hydraulic anomalies and issues with VLE data, efficiencies measured in one tower are extensible to others distilling the same system. A small allowance to variations in tray geometry as discussed above is in order. Caution is required with mixed aqueous-organic systems, where concentration may have a marked effect on physical properties, relative volatility, and efficiency. Table 14-12 shows typical tray efficiencies reported in the literature. 

Methods for predicting efficiency also parallel those for tray columns comparison against a similar installation, use of empirical methods, direct scaleup from laboratory or pilot plant, and use of theoretically derived models. Approaches by vendors of packing usually center on comparisons with similar installations (the so-called vendor experience ) and empirical approximations. Direct scaleup from small column studies is difficult with packed columns because of the unknown effects of geometrical factors and the variations of liquid distribution that are required for practical reasons. Theoretical or semitheoretical models are difficult to validate because of the flow effects on interfacial area. It may be concluded that there is no veiy good way to predict packed column efficiency, at least for the random type packings. 

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