Overall Efficiency

We define the overall tray efficiency EO as:

EO is applied throughout the whole column, i.e. every tray is assumed to have the same efficiency. The advantage is that it is simple to use, but it must be bear in mind that in actual practice, not all the trays have the same efficiency.

The advantage is that it is simple to use, but it must be bear in mind that in actual practice, not all the trays have the same efficiency.

The overall efficiency has been found to be a complex function of the following:

Geometry and design of the contacting trays

Flow rates and flow paths of vapour and liquid streams

Compositions and properties of vapour and liquid streams

From: "Separation Process Principles", J.D. Seader and E.J. Henley, p.292

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Values of EO can be predicted by any of the following 4 methods:

Comparison with performance data from industrial columns for the same or similar systems

Scale-up of data obtained with laboratory or pilot plant columns

Use of empirical efficiency models derived from data on industrial columns

Use of semi-theoretical models based on mass and heat transfer rates

The Drickamer-Bradford empirical correlation is given as:

The use of the equation is restricted to the range of data below, and is intended mainly for hydrocarbon mixtures.

Average temperature 157 - 420 oF
Pressure 14.7 - 366 psia
Liquid viscosity 0.066 - 0.355 cP
Overall Efficiency 41 - 88 %

The O'Connell correlation is given as:

( Viscosity measured in centiPoise )

The relative volatility is determined for the 2 key components at average column conditions.

[ See p.395 Example 7.7, "Separation Process Principles", J.D. Seader and E.J. Henley ]

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