Packing efficiency HETP prediction

Modeling and Prediction Maldistribution may drastically reduce packing efficiency. HETP may increase by a factor as high as 2 or 3 due to maldistribution. Shariat and Kunesh [lnd. Eng. Chem. Res., 34(4), 1273 (1995)] provide a good demonstration. 

In contrast, both expressed uncertainty in predicting packing efficiency. Harrison presented two case studies In one, adding water to two water-insoluble organics had no effect on HETP in another, a key... 

Lockett Chem. Eng. Progr., p. 60, January 1998) simplified the fundamental Bravo-Fair-Rocha correlation [Ind. Eng. Chem. Res. 35, p. 1660 (1996)] to derive an alternative rule of thumb for structured packing efficiency. This rule of thumb predicts HETPs under perfect distribution conditions. Lockett recommends caution when applying... 

The efficiency of a plate can be predicted with more certainty than the equivalent term for packing (HETP or HTU). 

Example 13.18 is included to show the predicted mass transfer efficiency of an acetone-water column in which structured packing is used. Of particular interest are the results from Eqs. 13.255, 13.259, 13.261 and 13.262 are used to determine transfer units. The value of HETP is calculated using Eq. 13.172. Plug flow of the phases is usually assumed, although extreme ratios of the flowing phases can cause some back mixing. 

In packed columns, it is conceptually incorrect to use the staged model even though it works if the correct height equivalent to a theoretical plate (HETP) is used. In this chapter we will develop a physically more realistic model for packed columns that is based on mass transfer between the phases. After developing the model for distillation, we will discuss mass transfer correlations that allow us to predict the required coefficients for common packings. Next, we will repeat the analysis for both dilute and concentrated absorbers and strippers and analyze cocurrent absorbers. A simple model for mass transfer on a stage will be developed for distillation, and the estimation of stage efficiency will be considered. After a mass transfer analysis of mixer-setder extractors. Section 16.8 and the appendix to Chapter 16 will develop the rate model for distillation. 

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