Mass transfer correlations for air stripping towers

The overall system‐specific liquid phase mass transfer coefficient, K L a, is the most important parameter in the design of air strippers. Designers frequently estimate K L a using a mass transfer correlations to avoid the cost of pilot tests. This paper evaluates the well‐accepted Onda correlations using a newly developed data base. Predictions based on the Onda correlations systematically overestimated K L a for packings typically used in full‐scale applications. They had an average error of ±40% and an average standard deviation of ±47%. The overestimation was a function of the packing diameter. A simple equation was developed to correct the Onda overestimation for packings larger than 1 inch (2.54 cm) in diameter, and it yielded predictions within ±20% range. The experimental K L a values obtained in this study varied with packing depth contradicting a basic assumption of the mass transfer theory, i.e., that K L a spatially is constant. Also, the effect of measurement errors of the variables involved in the calculation of both the experimental and the predicted K L a values were investigated. A large part of the observed difference between experimental and Onda predictions was attributed to a lack of fit of the Onda model. Thus, the quality of the predictive correlations can be improved.