Abstract
Published correlations for estimating the liquid phase mass transfer coefficients of structured packings are compared using experimental evidence on the efficiency of Montz-Pak B1–250MN and B1–500MN structured packings as measured in total reflux distillation tests using the chlorobenzene/ethylbenzene system at two operating pressures. Large differences are found between different correlations with respect to both the absolute values of mass transfer coefficients and the fraction of liquid phase based resistance and their trends with respect to increasing vapor and liquid loads. A new Delft Model liquid side mass transfer coefficient correlation that incorporates a more appropriate definition of the liquid film exposure length is presented which now generates lower values. The revised liquid film model, combined with an enhanced turbulent vapor phase mass transfer coefficient, leads to doubling the fractional liquid phase resistance with respect to that based on penetration theory assuming equal contact times. This effect results in predicting efficiencies which are slightly more conservative and agree reasonably well with experimental HETP data presented in this paper.
Highlights
Refining, gas processing, and commodity chemicals manufacturing plants around the world are continuously looking for ways to reduce energy requirements because of the immense costs associated with operation of large scale distillation facilities
This paper focuses on mass transfer coefficients, with particular emphasis on the qualitative and quantitative modeling aspects of the liquid phase related mass transfer resistance
Origins of this belief are difficult to trace but justification can be found in early studies conducted with a wetted wall falling film distillation column, indicating that not more than 10 % of total resistance to mass transfer lies in the liquid phase
Summary
Gas processing, and commodity chemicals manufacturing plants around the world are continuously looking for ways to reduce energy requirements because of the immense costs associated with operation of large scale distillation facilities. The liquid phase contribution could be even less pronounced for corrugated sheet structured packing Origins of this belief are difficult to trace but justification can be found in early studies conducted with a wetted wall falling film distillation column, (see, for example, Johnstone and Pigford8) indicating that not more than 10 % of total resistance to mass transfer lies in the liquid phase. This indication appears to be low when considering the results of theoretical and experimental studies conducted in mid and late 1970s by Sandall and co-workers.[9,10,11] Their theoretical and experimental effort has been arranged to allow direct determination of individual vapor and liquid phase mass transfer coefficients from falling film and packed column total reflux binary distillation studies They arrived at the conclusion that the liquid phase resistance is small but not negligible and should range somewhere between 12 and 18 %.11. Possible composition and relative volatility related effects are eliminated from consideration
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